Block 15 Step Pathology Prt 3

Explanation
The fungal elements in the biopsy tissue from the non-healing ulcer associated with nodular lymphangitis are likely to be that of Sporothrix schenckii, which shows characteristic thermal dimorphism. Thermal dimorphism is a characteristic of this fungus as it occurs in 2 different morphological forms depending on the temperature. Yeast forms are seen in the infected tissue and when grown in vitro at 35-37°C. Formation of mycelial phase is seen in nature and at room temperature (25-30 degrees).
Sporothrix schenckli occur as small oval, spindle shaped, or cigar shaped yeast cells in infected tissue and when grown at 37° in vitro. When cultured on Sabouraud's medium at 25°, produces grey to black colonies which become wrinkled and fuzzy with age. These colonies contain very thin (1-2 micron diameter) branching septate hyphae and small conidia (3-5 microns) arranged in flower-like clusters at the ends of tapering conidiophores.
Sporothrix schenckli causes subcutaneous mycosis known as sporotrichosis, a chronic granulomatous infection. The disease is characterized by development of nodules in skin and subcutaneous tissues which suppurate and break down to form indolent ulcers. The draining lymphatics become thickened and cord like. Multiple nodules develop along the lymphatics which also subsequently ulcerate. Disease characterized by single fixed nodule without involvement of lymphatics may be produced especially in endemic areas. Localization of infection occurs due to immunity.
The infection is reported to be endemic in Mexico and South America.
Lymphocutaneous infection, clinically resembling sporotrichosis, may be caused by other organisms like Nocardia brasiliensis, Mycobacterium rnarinum and Leishmania braziliensis. In the US, S. schenckli is the most commonly reported cause of this manifestation. Culture of biopsy specimen is important in confirming diagnosis.
S. schenckil occurs in nature as a saprophyte on plants, soil, timber, and a variety of vegetations. Infection usually occurs following thorn pricks or minor injuries and the fungal hyphal fragment or conidia being introduced through the traumatized skin. The disease is more often associated with certain occupations like in horticulturists, florists, and those engaged in gardening, farming, and hunting. Zoonotic transmission can also occur following contact with infected cats, dogs, and horses. Several cases of sporotrichosis acquired from cats have been reported from Brazil.
Systemic spread occurs rarely, causing arthritis or with involvement of central nervous system. Disseminated infections in immunocompromised patients have been reported.
Potassium iodide and itraconazole are used for treatment. In disseminated infections amphotericrn B is given. Cutaneous mycosis
is the fungal infection affecting the superficial keratinized tissue and involves skin, hair, and nails. The most important causative agents are dermatophytes belonging to 3 genera: trichophyton, epidermophyton, and microsporum.

Explanation
The viral agent responsible for the outbreak of gastroenteritis is most likely to be a Norovlrus. Norovirus (a group of Norwalk-like viruses) is the cause of >90% of non-bacterial gastroenteritis in the US and the most important cause of viral gastroenteritis involving adults. Food borne outbreaks are common. Uncooked or inadequately cooked shellfish is one of the important sources. Other viruses of gastroenteritis (Group A rotavirus, sapovirus, astrovirus, adenovirus types 40 and 41) are mostly associated with infections in children less than 5years old. Norovirus can survive at temperatures as high as 60°C and up to 10ppm chlorine. The virus does not possess the other characteristics listed.
NOROVIRUS genus belongs to the family Caliciviridae. The virus is non-enveloped, 27-40 nm in diameter, has a genome contains single-stranded RNA, replicates in the cytoplasm of the host cell, and is not cultivable. Genetic and antigenic diversity is an important characterisic of noroviruses. Genetic variability is likely to be responsible for repeated infections during a lifetime and high attack rates in all age groups during outbreaks. The prototype strain Norwalk virus caused an outbreak of gastroenteritis in a school in Norwalk, Ohio in 1968. Currently at least 4 norovirus genogroups (GI, Gil, GIII, & GIV) have been identified and these have been divided into at least 20 genetic clusters.
Transmission is by feco-oral route, through consumption of fecally contaminated water or food, or by direct person¬to-person spread. Shellfish harvested from fecally contaminated waters pose a special risk, as they possess the capacity to concentrate viruses through filtration. Contaminated fomites can be a source of infection. Vomitus contains the virus. Droplets resulting from aerosolization of vomitus can also be infective. Noroviruses are highly contagious and as few as 10 viral particles are sufficient to produce infection. The infection is often self-limited; rehydration by intravenous fluids is required in severe cases.
Recent data indicate that susceptibility to infection is genetically determined, people with 0 blood group being at greater risk of severe infection.
Laboratory diagnosis: A reverse-transcriptase polymerase chain reaction (RT-PCR) has been developed and is used by many state public health laboratories in the US for detection of norovirus in stool and vomitus samples. The test can be used to detect norovirus in shellfish and water samples as well. Other detection assays for noroviruses include enzyme immunoassay (EIA), electron microscopy, and immune electronnicroscopy (IEM).
Enzyme-linked immunosorbent (F LISA) assays developed for detection of IgM antibodies are not widely used due to limitations in detecting immune responses to a variety of antigenic types.
Researchers have suggested possible genomic recombination of human and animal noroviruses resulting in emergence of new strains.

Explanation
The patient's symptoms are suggestive of genital herpes, a widely prevalent sexually transmitted viral infection.
The major causative agent of genital herpes is Herpes simplex type 2 (HSV 2), accounting for 70-90% of primary genital herpes. Herpes simplex type 1 (HSV-1) also can cause genital herpes, though is mainly associated with oro¬pharyngeal infections. Both types share a significant number of common antigens.
An exception is Glycoprotein G, an envelope protein that elicits type-specific antibodies. Tests based on the recognition of antibodies to glycoprotein G antigens of FISV-1 (gG-1) and HSV-2 (gG-2) accurately distinguishes between HSV-1 and HSV-2 infections. Recurrence of genital herpes in I-ISV-2 infection is much more than in infection by HSV-1. High rates of HSV-2 infection are seen in HIV type-1 infected persons. Differentiation of the types and detection of HSV-2 infections is important in assessment of prognosis, management, and counseling of patients.
Other features listed are not characteristics of Herpes simplex virus.
Herpes simplex is a DNA virus, with the virus having a short replication cycle requiring only 8-16 hours for completion. Though human diploid fibroblasts are often preferred for growing the virus, it can grow in a variety of tissue culture cells and also on chorioallantoic membrane of chick embryo. The virus produces intranuclear eosinophilic inclusions in the infected cells, and the site of latency is a sensory ganglion.
In primary genital herpes, appearance of vesiculo-ulcerative lesions is often associated with systemic symptoms. Virus remains latent in sacral ganglia and leads to recurrent infections, mostly in HSV-2 infections. Asymptomatic infections are common. Both symptomatic and asymptomic infections serve as reservoirs of the virus.
Genital herpes during pregnancy presents great risk of transmitting infection to the newborn, resulting in neonatal herpes. HSV2 infection is known to enhance HIV susceptibility and subsequent sexual transmission because of the break in mucosal surface caused by the ulcerative lesions. Progressive disease and severe extensive lesions are seen in immunocompromised individuals.
Laboratory diagnosis of genital herpes is mainly based on virological tests and type-specific serological assays.
a. Virological tests include detection of viral antigen by direct fluorescent antibody test (DFA), viral culture, and Polymerase chain reaction (PCR) assay for detection and identification of the virus type. DFA does not identify HSV type and is less sensitive. PCR and culture yield positive results only during phases of active infection. Culture, though highly specific, is less sensitive. PCR is not widely available for use.
b. Type-specific serology using glycoprotein G antigens (gG-1 and gG-2) is recommended for confirming or establishing clinical diagnosis in symptomatic patients with negative culture and antigen testing and those with atypical presentations. The assays are used also for screening of high-risk populations. Enzyme Linked Imrnunosorbent Assay (ELISA), immunoblot tests, and a rapid membrane-based immunoassay for HSV-2 are available for detection of type-specific antibodies.

Acyclovir, famciclovir, and valacyclovir are drugs used for treatment of genital herpes. They reduce subclinical viral shedding and decrease frequency and severity of recurrent outbreaks.

Explanation
Paramyxoviruses of human importance are Parainfluenza viruses, Respiratory syncytial virus (RSV), Mumps, Measles (rubeola), and Newcastle disease viruses. Of these RSV is the only virus that lacks in haemagglutinating and neuraminidase activities. RSV is the major respiratory pathogen of young children and the foremost
cause of lower respiratory tract infections in the form of bronchiolitis and pneumonia in infants. Epidemics are frequent in late fall and winter. RSV is an important rosocomial pathogen. It can be concluded that RSV is responsible for the nosocomial outbreak in the pediatric ward.
Transmission of RSV occurs through respiratory secretions by direct contact with the infected person or through contaminated fomites. Inhalation of aerosols produced by coughing and sneezing can cause infection. Touching the contaminated fomites results in contamination of fingers. Accidental self-inoculation of nares or conjunctiva by contaminated finger leads to infection. Nosocomial transmission often occurs via health care personnnel. Contact isolation precautions are necessary to manage RSV nosocomial outbreaks. These include isolation of infected patients, restriction of visitors, and strict adherence of medical personnel to contact precautions such as hand washing, wearing gowns and gloves, masks, and eye protection.
RSV infection does not show the other features listed.
Maternal antibodies are not found to be protective. Rates of illness are highest among 1 to 6-month-old infants and severe illness has been observed in infants with moderate level of maternal antibodies. Nasal IgA neutralizing antibodies are thought to have more protective effect than serum antibodies. Cell mediated immunity is thought to play an important role in protection against RSV infection.
Re-infections are common and infected older children and adults get common cold-like symptoms. Severe lower respiratory tract disease can occur in elderly and immunocompromised persons.
Immunoprophylaxis is not used for controlling spread during outbreaks in health-care settings as in pediatric wards. Immunoprophylaxis (RSV immunaglobulin or monoclonal antibodies) is used to protect children at risk, such as prematurely born infants and children

Explanation
The clinical features described are typical of congenital cytomegalic inclusion disease caused by cytomegalovirus (CMV), and the virus grows in vitro only on human fibroblastic cells.
Among the beta-herpes viruses, CMV is the one associated with congenital infection. The virus is very species specific. Human cytomegalovirus grows in vitro only on human fibroblastic cells. Though epithelial cells are affected in vivo, they are not susceptible in vitro. The other features listed are not properties of Clv1V. CMV does not grow either on monkey kidney cells or embryonated eggs. Cytomegalovirus replicates slowly unlike the alpha herpes viruses which have a short replicative cycle of 12-18 hours. The virus is well known for producing life long latent infections, the sites of latency are mainly secretary glands and kidneys not sensory ganglia. Sensory ganglia are the sites of latency for Herpes simplex and Varicella- Zoster which belong to alpha- herpesviruses. Cytomegalovirus does not show antigenic cross reaction with other herpes viruses.
CMV when grown on human fibroblastic cells produces a characteristic cytopathic effect. Many affected cells become enlarged. Giant cells with large intranuclear acidophilic inclusions (owl eye inclusions) and perinuclear cytoplasmic inclusions are seen. Virus replicates very slowly and infection spreads from cell to cell. It may take several days for the entire rnonolayer to be infected. Inclusion-bearing cytomegalic cells can be demonstrated in centrifuged deposit of urine and in other clinical samples from infected tissues.
In the US, up to 80% of adults show antibodies to the virus indicating high prevalence of the infection. CMV is the most frequent congenitally transmitted virus in the country. Each year about 40,000 children are born with congenital cytomegalovirus infection.
Congenital CMV disease causes estimated 400 deaths each year and leaves approximately 8,000 with permanent disabilities like mental retardation, hearing loss, and ocular impairment. Fetal death or generalized cytomegalic inclusion disease results when the mother acquires and transmits primary Clv1V infection to the fetus during the first trimester of pregnancy. Reactivated maternal infections may not cause fetal damage. Perinatal infection of the new born can occur from the mother's birth canal or breast milk.
Spread of the virus is predominantly by close contact and through oral and respiratoy routes. In immunocompetent persons usually the infection is subclinical. The virus sometimes causes heterophil antibody negative mononucleosis. This most commonly follows transfusion of CMV infected blood (post-transfusion mononucleosis). CMV is an important pathogen in patients with AIDS. The already weakened immune response is further damaged by the nonspecific CMI-inhibiting effect of CMV. Disseminated and often fatal infections are produced with manifestations such as chorioretinitis, gastroenteritis and pneumonia. Immunosuppressed individuals like organ transplant recipients are also at high risk of developing severe CMV disease. Often development of illness may be due to reactivation of their own latent virus.
Laboratory diagnosis consists of microscopy for cytornegalic cells in urine and saliva, isolation of the virus on
human fibroblastic cells from clinical specimens like urine, saliva and other body fluids, detection of viral antigens in leukocytes carrying the virus, using monoclonal antibodies, and detection of viral DNA by molecular methods. Polymerase chain reaction assays (PCR) are used for detection of viral load in samples like blood and urine. Quantitative PCR assays can be useful for monitoring viral load during antiviral treatment.
Serological tests include detection of specific IgM and IgG antibodies by enzyme-linked immuncsorbant assay (ELISA). CMV mononucleosis can be best diagnosed by positive IgM serology. In most European countries, pregnant women are tested for CMV during the first trimester of pregnancy by screening for anti-CMV IgM. IgM antibodies may not always indicate primary infection, as they are produced during reactivation and reinfection. IgG antigen avidity test is reported to be of use to differentiate primary and non-primary infections. Low avidity antibodies are produced at the onset of infection. Serological tests are not very helpful for diagnosis of CMV infection in imrnunosuppressed persons. Serological screening of transplant donors may be helpful to prevent some primary CMV infections.
Ganciclovir has been successfully used for life-threatening CMV infections in immunosuppressed patients. Progressive hearing loss in neonates with congenital infection can be controlled by this drug. Foscarnet is a drug recommended for treatment of CMV retinitis. Both drugs are used for anti-CMV prophylaxis in transplant recipients.
There is ongoing research on development of a suitable vaccine.

Explanation
Parvovirus B19 is a member of the family Parvoviridae and is the causative agent of erythema infectiosum (fifth disease). The hallmark symptom of erythema infectiosum is a mild rubella-like erythematous rash that produces arthropathy, especially in women. The disease has 2 separate components. The first component is the lytic phase where the lytic action of the virus replication in erythroid precursors gives rise to a transient arrest of erythrocytic production. This can result in a slight drop in hemoglobin. Hemoglobin levels will substantially drop in those patients with chronic hemolytic anemia. This is the viremic stage, and mild flu-like symptoms with pyrexia and chills are not uncommon. These flu-like symptoms can last for 1 to 3 days. 1 week after the viremia peak, the second phase occurs where the virus is rarely detectable. The second phase is where the erythematous maculopapular rash and arthropathy occur. Erythema infectiosum infections in pregnant women can induce fetal loss (5-20%). No evidence of congenital abnormalities due to erythema infectiosum has been documented.
Herpes simplex type 1 (HSV-type 1) belongs to the family Herpes viridae and causes an infection that characteristically presents as an eruption of vesicles that are restricted to areas around the mouth, lips, and nostrils. The infection can also occur in the genital area, thought HSV-type 2 is more commonly associated with genital infections, called herpes labialis. Patients usually can predict the onset of an eruption due to a prodromal stage of itching or other sensations that can occur a few hours to a few days prior to the eruption of vesicles. HSV¬type 1 also causes primary infections of the oral mucous membranes in children and herpetic eye infections. Eruptions can occur at any time and depend on the immunological status of the host, health, and various other factors that vary from host to host.
Herpes simplex type 2 (HSV-type 2) belongs to the family Herpesviridae and causes an infection that characteristically presents as an eruption of vesicles that are restricted to areas around the genital area. Multiple vesicles in females appear on the vulva, in the vagina, and on the portio. Multiple vesicles in men are found often on the sulcus of the glans and the preputium but can be found on any part of the penis. Duration and severity of the eruptions are usually more severe in females than in males. 1-15V-type 1 can also be found to cause genital eruptions but at a significantly lower rate. HSV-type 2 causes 75% of all neonatal herpes (a severe complication of genital HSV infection) where the newborn acquires
the virus by contamination through the birth canal. Eruptions can occur at any time and depend on the immunological status of the host, health, and various other factors that vary from host to host.
Epstein-Barr virus belongs to the family Herpesviridae and is the causative agent of infectious mononucleosis (IM), Burkitt's Lymphoma, and undifferentiated nasopharyngeal carcinoma. IM characteristically produces a marked lymphocytosis involving almost all of the lymphoreticular tissues. This leads to hepatomegaly, splenomegaly, lymphadenopathy, and lymphoid hyperplasia of the oronasopharynx. The peripheral blood smear contains atypical lymphocytes of the Downey II type. It is generally a self-limiting disease; however, it can cause a severe protracted illness that can at times prove to be fatal. Patients with an unusual immuno-defect known as the X-linked lymphoproliferative syndrome frequently have overwhelming EBV primary infections, which can be fatal in the majority of the cases.
Cytomegalovirus (CMV) belongs to the family Herpesviridae and causes cytomegalovirus mononucleosis, cytomegalic inclusion disease, and cytomegalovirus infection in the immunocompromised. CMV resembles infectious mononucleosis in that atypical lymphocytosis, fever, and malaise are characteristic symptoms to both. Pharyngitis
is present as a symptom, though less severe in CMV than in infectious mononucleosis. The heterophile antibody test is also negative in CMV. Toxoplasmosis may also mimic CMV and infectious mononucleosis and thus must be considered in the differential diagnosis in those patients with a negative heterophile antibody test and mono-like symptoms.
Varicella-zoster virus is a member of the family Herpesviridae and is the causative agent of Varicella (chickenpox) and herpes zoster (shingles). Varicella is highly communicable in children. Varicella usually has an acute onset with fever and a progressive rash that leads to the formation of vesicles. These vesicles eventually crust over. They can form on the mucous membranes of the mouth (most commonly the palate area), as well as on the skin. Cutaneous eruptions appear early and most profusely on areas of the back, abdomen, and chest. The palpebral conjunctiva, trachea, larynx, rectal, and vaginal mucosa may also become involved. In adults, older children, and children with primary immunodeficiency or deficient cell-mediated immunity, the infection is more severe than in healthy children. Fevers are usually more prolonged in duration and higher; the rash is more profuse; constitutional symptoms are more severe; and complications are often more common.

Explanation
The rash described is that of secondary syphilis, caused by Treponema pailidurn. Involvement of palms and soles by a rash is unusual, and secondary syphilis should come to mind. Not all patients with secondary syphilis have a severe form of the rash, and consequentially some cases are missed.
Primary syphilis takes the form of a painless, button-like mass called chancres. Tertiary syphilis, which is now rare, has a propensity for involving the aorta and central nervous system and can also cause "gummas" (granulomatous¬like lesions) in many sites, notably including the liver and bone.
Herpes simplex I usually causes perianal vesicular lesions. Herpes simplex II usually causes genital vesicular lesions.
HIV does not itself cause a rash; although, co-infection with other organisms can result in a rash
Neisseria gonorrhoeae does not typically cause a rash.

Explanation
Squamous cell carcinoma is the most common tumor arising inthe sun-exposed areas in older people. It is relatively rare in African-American people in whom the tumor often arises in association with scarring processes. The most accepted cause for the tumor is exposure to ultraviolet light with subsequent DNA damage and associated mutagenicity. They may arise at the sites of chroniculceration, trauma, burns, fistulous tract and an increased incidence is noticed in patients with Xeroderma pigmentosum.
Clinically, they present as shallow ulcers often with keratinous crust and ulcerated, indurated surrounds. The adjacent skin shows features of actinic damage. Microscopically, it consists of nests of squamous epithelial cells, which arise from the epidermis and extend into the dermis for a variable distance. The cells have abundant cytoplasm and large vesicular nucleus. There is variable central keratinization with horn pearl formation depending on the degree of differentiation. Squamous cell carcinoma is graded based on the degree of anaplasia into well, moderately and poorly differentiated lesions. Invasive squamous cell carcinoma is usually discovered while they are small and resectable, less than 5% metastasize to distant lymph nodes.
BASAL CELL CARCINOMAS are the most common cutaneous tumors accounting for approximately 70% of all the malignant diseases of the skin. They are slow growing and rarely metastasize. They are found predominantly in areas of skin exposed to the sun, particularly in fair-skinned individuals. Up to 80% of them are found in the head and neck regions. They are common in males. They tend to occur in older people although they have also been found in children and young adults.
The clinical presentation can be variable. It may be apapula-nodular lesion with a pearly translucent edge, anulcerated destructive lesion (rodent ulcer), a pale plaque with variable induration, an erythematous plaque, or a partly cystic nodule. On histological examination, tumor cells resemble those in the normal basal cell layer of the epidermis. They are composed of islands of basaloid cells with palisading of the cells at the periphery. The tumor cells have a hyperchromatic nucleus with little poorly defined cytoplasm. Ulceration is seen in larger lesions and aggressive tumors may extend into the lower dermis.
Merkel cell carcinoma, a rare neoplasm is derived from the Merkel cell of the epidermis, a neural crest derived cell putatively important for tactile sensation in lower animals. They are potentially lethal tumors. They are composed of small round malignant cells containing neurosecretory granules.
KERATOACANTHOMA is a rapidly developing neoplasm, which may heal spontaneously with out treatment. Histologically, they may mimic squamous cell carcinoma. It affects sun-exposed areas of skin of whites older than 50 years especially in the cheeks, nose, ears, and the dorsa of the hands. Males are more affected then females. Clinically, they appear as flesh colored dome-shaped nodules with a central keratin filled plug, imparting a crater Like topography. They range in size from 1cm to several centimeters. Microscopically,there is central keratin filled crater with squamous epithelium growing downward into the dermis as irregular tongues. The epithelium has large cells showing evidence of reactive cytologic atypia and abrupt keratinization.
SEBORRHEIC KERATOSIS affects the middle aged or older individuals arising in the trunk, extremities, head, and neck regions. Clinically, they appear as round flat plaques that vary in diameter from millimeters to several centimeters. They are uniformly tan to dark brown and usually show a velvety to granular surface. Microscopically, they are exophytic neoplasms and demarcated sharply form the adjacent epidermis. They are composed of sheets of small cells that most resemble basal cells of the normal epidermis. There is hyperkeratosis and small keratin filled cysts called as horn cysts with down growths of keratin in the main tumor mass forming pseudo horn cysts are seen characteristically. When they are inflamed, they undergo squarnous differentiation and show foci of squamous cells resembling eddy currents in a stream.

Explanation
Squamous cell carcinoma is the most common tumor arising inthe sun-exposed areas in older people. It is relatively rare in African-American people in whom the tumor often arises in association with scarring processes. The most accepted cause for the tumor is exposure to ultraviolet light with subsequent DNA damage and associated mutagenicity. They may arise at the sites of chroniculceration, trauma, burns, fistulous tract and an increased incidence is noticed in patients with Xeroderma pigmentosum.
Clinically, they present as shallow ulcers often with keratinous crust and ulcerated, indurated surrounds. The adjacent skin shows features of actinic damage. Microscopically, it consists of nests of squamous epithelial cells, which arise from the epidermis and extend into the dermis for a variable distance. The cells have abundant cytoplasm and large vesicular nucleus. There is variable central keratinization with horn pearl formation depending on the degree of differentiation. Squamous cell carcinoma is graded based on the degree of anaplasia into well, moderately and poorly differentiated lesions. Invasive squamous cell carcinoma is usually discovered while they are small and resectable, less than 5% metastasize to distant lymph nodes.
BASAL CELL CARCINOMAS are the most common cutaneous tumors accounting for approximately 70% of all the malignant diseases of the skin. They are slow growing and rarely metastasize. They are found predominantly in areas of skin exposed to the sun, particularly in fair-skinned individuals. Up to 80% of them are found in the head and neck regions. They are common in males. They tend to occur in older people although they have also been found in children and young adults.
The clinical presentation can be variable. It may be apapula-nodular lesion with a pearly translucent edge, anulcerated destructive lesion (rodent ulcer), a pale plaque with variable induration, an erythematous plaque, or a partly cystic nodule. On histological examination, tumor cells resemble those in the normal basal cell layer of the epidermis. They are composed of islands of basaloid cells with palisading of the cells at the periphery. The tumor cells have a hyperchromatic nucleus with little poorly defined cytoplasm. Ulceration is seen in larger lesions and aggressive tumors may extend into the lower dermis.
Merkel cell carcinoma, a rare neoplasm is derived from the Merkel cell of the epidermis, a neural crest derived cell putatively important for tactile sensation in lower animals. They are potentially lethal tumors. They are composed of small round malignant cells containing neurosecretory granules.
KERATOACANTHOMA is a rapidly developing neoplasm, which may heal spontaneously with out treatment. Histologically, they may mimic squamous cell carcinoma. It affects sun-exposed areas of skin of whites older than 50 years especially in the cheeks, nose, ears, and the dorsa of the hands. Males are more affected then females. Clinically, they appear as flesh colored dome-shaped nodules with a central keratin filled plug, imparting a crater Like topography. They range in size from 1cm to several centimeters. Microscopically,there is central keratin filled crater with squamous epithelium growing downward into the dermis as irregular tongues. The epithelium has large cells showing evidence of reactive cytologic atypia and abrupt keratinization.
SEBORRHEIC KERATOSIS affects the middle aged or older individuals arising in the trunk, extremities, head, and neck regions. Clinically, they appear as round flat plaques that vary in diameter from millimeters to several centimeters. They are uniformly tan to dark brown and usually show a velvety to granular surface. Microscopically, they are exophytic neoplasms and demarcated sharply form the adjacent epidermis. They are composed of sheets of small cells that most resemble basal cells of the normal epidermis. There is hyperkeratosis and small keratin filled cysts called as horn cysts with down growths of keratin in the main tumor mass forming pseudo horn cysts are seen characteristically. When they are inflamed, they undergo squarnous differentiation and show foci of squamous cells resembling eddy currents in a stream.

Explanation
SEBORRHEIC KERATOSIS affects the middle aged or older individuals arising in the trunk, extremities, head, and neck regions. Clinically, they appear as round flat plaques that vary in diameter from millimeters to several centimeters. They are uniformly tan to dark brown and usually show a velvety to granular surface. Microscopically, they are exophytic neoplasms and demarcated sharply form the adjacent epidermis. They are composed of sheets of small cells that most resemble basal cells of the normal epidermis. There is hyperkeratosis and small keratin filled cysts called as horn cysts with down growths of keratin in the main tumor mass forming pseudo horn cysts are seen characteristically. When they are inflamed, they undergo squarnous differentiation and show foci of squamous cells resembling eddy currents in a stream.


Squamous cell carcinoma is the most common tumor arising inthe sun-exposed areas in older people. It is relatively rare in African-American people in whom the tumor often arises in association with scarring processes. The most accepted cause for the tumor is exposure to ultraviolet light with subsequent DNA damage and associated mutagenicity. They may arise at the sites of chroniculceration, trauma, burns, fistulous tract and an increased incidence is noticed in patients with Xeroderma pigmentosum.
Clinically, they present as shallow ulcers often with keratinous crust and ulcerated, indurated surrounds. The adjacent skin shows features of actinic damage. Microscopically, it consists of nests of squamous epithelial cells, which arise from the epidermis and extend into the dermis for a variable distance. The cells have abundant cytoplasm and large vesicular nucleus. There is variable central keratinization with horn pearl formation depending on the degree of differentiation. Squamous cell carcinoma is graded based on the degree of anaplasia into well, moderately and poorly differentiated lesions. Invasive squamous cell carcinoma is usually discovered while they are small and resectable, less than 5% metastasize to distant lymph nodes.
BASAL CELL CARCINOMAS are the most common cutaneous tumors accounting for approximately 70% of all the malignant diseases of the skin. They are slow growing and rarely metastasize. They are found predominantly in areas of skin exposed to the sun, particularly in fair-skinned individuals. Up to 80% of them are found in the head and neck regions. They are common in males. They tend to occur in older people although they have also been found in children and young adults.
The clinical presentation can be variable. It may be apapula-nodular lesion with a pearly translucent edge, anulcerated destructive lesion (rodent ulcer), a pale plaque with variable induration, an erythematous plaque, or a partly cystic nodule. On histological examination, tumor cells resemble those in the normal basal cell layer of the epidermis. They are composed of islands of basaloid cells with palisading of the cells at the periphery. The tumor cells have a hyperchromatic nucleus with little poorly defined cytoplasm. Ulceration is seen in larger lesions and aggressive tumors may extend into the lower dermis.
Merkel cell carcinoma, a rare neoplasm is derived from the Merkel cell of the epidermis, a neural crest derived cell putatively important for tactile sensation in lower animals. They are potentially lethal tumors. They are composed of small round malignant cells containing neurosecretory granules.
KERATOACANTHOMA is a rapidly developing neoplasm, which may heal spontaneously with out treatment. Histologically, they may mimic squamous cell carcinoma. It affects sun-exposed areas of skin of whites older than 50 years especially in the cheeks, nose, ears, and the dorsa of the hands. Males are more affected then females. Clinically, they appear as flesh colored dome-shaped nodules with a central keratin filled plug, imparting a crater Like topography. They range in size from 1cm to several centimeters. Microscopically,there is central keratin filled crater with squamous epithelium growing downward into the dermis as irregular tongues. The epithelium has large cells showing evidence of reactive cytologic atypia and abrupt keratinization.

Explanation
BASAL CELL CARCINOMA usually begins as a small indented nodule localized around hair follicles, typically in sun exposed regions of the skin. It typically begins to form an ulcerated center as it enlarges. This type of tumor rarely metastasizes but is locally invasive. It can be quite disfiguring. Excision is necessary to prevent its spread.
MELANOMA is typically a highly pigmented tumor of the skin, often seen in sun exposed regions. This tumor metastasizes widely and early on. The lesion may be a constellation of pigment colors, ranging from black to blue to red. The borders are frequently uneven. Tumors may arise from other organs including the meninges, throat (pharynx and larynx), and eye. Satellite nodules may arso be seen distant from the main tumor site. Due to the aggressive character of this tumor, wide and deep incisions are necessary, along with tumor staging, if there is the possibility of metastasis.
MOLLUSCUM CONTAGIOSUM is caused by a large DNA pox virus. This disease is typically seen in children and sexually active young adults. The lesion presents as a pearly, flesh colored papule approximately 2-10mm in diameter, often with a central umbilication. These lesions are often seen on the skin or mucous membranes. Treatment includes currettage and dessication or liquid nitrogen. Diagnosis is supported by the presence of intracytoplasmic inclusions in a KOH preparation of crushed tissue.
SQUAMOUS CELL CARCINOMA is also a slow growing tumor often found on sun exposed surfaces of the skin. This cancer does eventually metastasize. The lesion appears as a raised plaque which tends to ulcerate. Unlike basal cell carcinomas, this tumor originates in skin and squamous mucosa, which can result in lesions involving the skin, cervix, tongue, esophagus and lips. Histologically, this tumor may range from a more indolent type of tumor, containing keratin pearls of concentric lamellated keratin to a very anaplastic nature, where no pearls are evident. Squamous cell carcinoma metastasizes via lymphatics and then to the rest of the body. Excisional biopsy is required to determine the type of skin cancer and treatment necessary.
LIPOMA is a subcutaneous, soft round to oval mass of fatty connective tissue. The lesion is approximately 3-5mm in diameter and surrounded by a delicate capsule. The lipoma is normally a benign growth, but constant enlargement may cause compressive effects on surrounding tissues. Local excision is the usual mode of treatment.

Explanation
This patient has nodular melanoma. The early signs of melanoma include ABCDEs: asymmetry of lesion; border irregularity, bleeding, or crusting; color change or variegation; diameter over 6 mm or growing lesion; elevated area (or palpable papule) in a previously flat nevus.
The history in this patient (rapid onset, bleeding after minor scratching, blue-black nodule) is highly suggestive of nodular melanoma. This subtype is seen in approximately 15% of cases.
The most common subtype of melanoma is superficial spreading. Superficial spreading melanoma starts as a deeply pigmented macule or plaque with intact skin markings.
LENTIGO MALIGNA melanoma occurs almost exclusively on the sun-exposed skin of the head and neck. Lentigo maligna melanoma arises from lentigo maligna, a melanoma in situ.
AMELANOCYTIC melanomas are very rare, and have no pigment.
ACRAL LENTIGOUS melanomas are more common in African-Americans. Clinically, the lesion is characterized by a tan, brown-to-black, flat macule with color variegation and irregular borders. They are occasionally found in nail beds.

Explanation
The correct answer choice is lung cancer. The patient most probably has dermatomyositis. The clinical presentation of proximal muscle weakness, purplish discoloration in her periorbital region (heliotrope lids) is highly suggestive of the condition. Heliotrope lids and Gottron's papules are classically associated with this condition. One of the major long-term complications of dermatomyositis is malignancy, such as lung cancer.
Celiac disease presents with diarrhea and a rash known as dermatitis herpetiformis.
Polymyalgia rheumatica presents with muscle weakness, primarily of the shoulder girdle and lower back. This condition is often associated with Giant Cell Arteritis (GCA), a condition that more commonly affects the elderly. Patients with GCA present with headaches, temporal artery tenderness, elevated ESR, and a potential for blindness if left untreated.
Myasthenia gravis presents with progressive muscle weakness during the day, diplopia, and is not associated with a characteristic rash but is associated with thymomas. The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest.
Guillain Barre syndrome is a disorder caused by nerve inflammation leading to progressive muscle weakness or paralysis, which typically follows an infectious illness.

Explanation
Your patient most probably has vitiligo. Vitiligo is the most common multifactorial depigmentary disorder of the skin and results from the selective destruction of nnelanocytes. It generally appears between 15 to 25 years of age. A Wood's lamp is a diagnostic tool used in dermatology by which ultraviolet light is applied onto the skin of the patient; a technician then observes any subsequent fluorescence. Woods lamps will differentiate hypopignnentation that occurs in many skin diseases from depigmentation occurring in vitiligo. Because vitiligo is associated with an increased risk of autoimmune thyroid disease, especially Hashimoto's thyroiditis, the thyrotropin level should be measured annually. Patients should routinely be asked whether there is a family history of vitiligo and premature hair graying and whether there is a family or personal history of thyroid disease or other autoirnmune diseases (e.g., alopecia areata, rheumatoid arthritis, diabetes, and pernicious anemia).
Bacterial skin infection does not cause vitiligo.
Viral skin infection does not cause vitiligo.
Skin traumas will leave scars.
It is not advisable to add additional salt to foods, but not because of the risk of developing vitiligo.

Explanation
This patient suffers from xeroderma pigmentosum. This disease is found in approximately 1/250,000 people worldwide. It is caused by an autosomal recessive mutation found in all races of the human population. It is primarily manifest as an extreme sensitivity of the skin and other exposed portions of the body to ultraviolet light. In some varieties of xeroderma pigmentosum, systemic effects, e.g damage to the central nervous system, are also observed.
In some cases of xeroderma pigmentosum, there have been reports of a genetic defect in excision repair of damaged DNA. One potential mechanism for ultraviolet light-induced damage to DNA is the formation of thymine dimers between adjacent thyrnine residues of one strand of the DNA double helix. Several mechanisms for repair of damage to DNA have been discovered in bacterial systems. For example, excision repair first utilizes an endonuclease. The endonuclease recognizes abnormal DNA near the 5' side of the thymine dimer, causing the damaged strand to separate from the double helix. Next, a DNA polymerase forms a new polynucleotide to replace the damaged sequence. Finally, a 5`-exonuclease removes the damaged sequence and a DNA ligase closes the break, resulting repair.

Explanation
PARAKERATOSIS indicates that the cells in the stratum corneum have retained their nuclei. This is seen in conditions with rapid keratin formation, such as psoriasis.
HYPERKERATOSIS is an increase in the stratum corneum.
ACANTHOSIS is hyperplasia of the stratum spinosum.
SPONGIOSIS is edema in the epidermis.
KERATOSIS is a well-defined lesion of the epidermis with an increase of the stratum correum.

Explanation
Impetigo is a contagious pyogenic infection classified into bullous and non-bullous types. The non-bullous type is caused by Staphylococcus aureus or Streptococcus pyogenes and is more common on the exposed parts of the body. An initial breach in skin barrier by trauma, insect bite, etc. occurs, followed by infection. It is most common in the age group 2 to 5 years and in those having in poor hygiene or overcrowded settings. It is a self-limiting condition and heals without scarring in a few weeks. Treatment aids in reducing transmission and relieving discomfort. Treatment is with proper wound care and topical antibiotics such as mupirocin or retapamulin. The bullous type is characterized by large bullae, along with fever, diarrhea, weakness, etc.
Carbuncle is a large abscess on the skin, also caused by Staphylococcus aureus. There is pus drainage onto the skin. Cellulitis is a diffuse infection of the skin, presenting with fever and tight, warm inflamed skin, and necrotizing fasciitis, involving deep fascia along with necrosis of subcutaneous tissues.
Furuncle is a type of folliculitis, involving the hair follicle.
The vesicles and honey-colored crusts are more indicative of impetigo and not the other conditions.
Topical or oral steroids are not indicated in skin infections. Oral antibiotics are usually not necessary in non-bullous impetigo, although they may be indicated in extensive bullous lesions. Emollients are not necessary in impetigo.

Explanation
Impetigo is a contagious pyogenic infection classified into bullous and non-bullous types. The non-bullous type is caused by Staphylococcus aureus or Streptococcus pyogenes and is more common on the exposed parts of the body. An initial breach in skin barrier by trauma, insect bite, etc. occurs, followed by infection. It is most common in the age group 2 to 5 years and in those having in poor hygiene or overcrowded settings. It is a self-limiting condition and heals without scarring in a few weeks. Treatment aids in reducing transmission and relieving discomfort. Treatment is with proper wound care and topical antibiotics such as mupirocin or retapamulin. The bullous type is characterized by large bullae, along with fever, diarrhea, weakness, etc.
Carbuncle is a large abscess on the skin, also caused by Staphylococcus aureus. There is pus drainage onto the skin. Cellulitis is a diffuse infection of the skin, presenting with fever and tight, warm inflamed skin, and necrotizing fasciitis, involving deep fascia along with necrosis of subcutaneous tissues.
Furuncle is a type of folliculitis, involving the hair follicle.
The vesicles and honey-colored crusts are more indicative of impetigo and not the other conditions.
Topical or oral steroids are not indicated in skin infections. Oral antibiotics are usually not necessary in non-bullous impetigo, although they may be indicated in extensive bullous lesions. Emollients are not necessary in impetigo.

Explanation
TINEA VERSICOLOR (Pityriasis versicolor) is a mild superficial infection of the skin. It is characterized by multiple, usually asymptomatic, scaly patches varying from white to brown in color. They are most frequently seen on chest, neck, and abdomen and occasionally on the face. The condition is usually seen in young adults.
Diagnosis of this condition is made on the basis of clinical findings. On microscopic examination of scraping from the lesion under a woods lamp, yeast and short plump golden hyphae are seen.
Treatment of T. versicolor involves topical therapy with selenium sulfide, imidazoles, and zinc pyrithiore.
Hypopigmented patches can be distinguished from Vitiligo on the basis of appearance. Vitiligo usually presents as periorificial lesions or lesions on the tips of fingers. It is characterized by a loss and not just a lessening of pigmentation (as in T. versicolor)
TINEA CRURIS is confined to the groin region and the gluteal cleft and is associated with severe itching and a rash. The margins of the rash are sharp, with cleared centers. The area is hyperpigmented on resolution. Treatment involves the use of drying powders, ketoconazole cream, and in severe cases, systemic ketoconazole.
Leprosy is associated with pale anesthetic macular skin lesions. There is associated nerve thickening with the associated anesthesia. There is also accompanying history of living in an endemic area in childhood.
TINEA CAPITIS is a disease caused by superficial fungal infection of the skin of the scalp, eyebrows, and eyelashes, with a propensity for attacking hair shafts and follicles. The disease is considered to be a form of superficial mycosis or dermatophytosis. Several synonyms are used, including ringworm of the scalp and tinea tonsurans.

Explanation
The bacterial enzyme DNA gyrase is equivalent to the eukaryotic topoisomerase. Ciprofloxacin and other drugs of this class including nalidixic acid, levofloxacin, and gemifloxacin inhibit bacterial DNA gyrase. Gyrase is an enzyme necessary for DNA replication and functions to remove the positive supercoiling of the DNA which occurs as the DNA strands unwind to allow DNA polymerase to access the single stranded DNA template. There are 2 classes of mammalian topoisomerases, Type I and Type II. The major difference between the two is that the Type I topoisomerase introduces a single stranded nick in the DNA in the process of relieving the supercoiling, while the Type II enzyme introduces a double stranded nick in the DNA.
DNA polymerase is the enzyme responsible for polymerizing the DNA during the replication process in both prokaryotes and eukaryotes. The helicase unwinds the DNA helix during replication while primase synthesizes the RNA primer required for DNA polymerase to initiate replication of the DNA. DNA ligase is responsible for joining fragments of DNA such as those formed on the lagging strand during replication.

Explanation
The clinical presentation is suggestive of bacterial vaginosis caused by Gardnerella vaginalis. Patients present with a malodorous, grayish white vaginal discharge. On examination, the vulva and vagina are not inflarnmed. The discharge gives off an amine or fishy odor when mixed with potassium hydroxide. Microscopy reveals clue cells and a few leukocytes. Treatment is with rnetronidazole.
Patients with Candida albicans vaginal infection present with white, non-foul smelling discharge. On examination, the vulva and vagina are erythematous with fissures and even lacerations, as it is pruritic. Oral fluconazole or clotrimazole creams are used to treat it.
Patients with chancroid, which is caused by Haernophilus ducreyi, present with painful genital ulcers and suppurative inguiral lymphadenopathy. Azithromycin is used for treatment.
Patients with Herpes Zoster, which is caused by the Varicella-zoster virus, present with a painful, vesicles in a unilateral dermatomal distribution. Farnciclovir is used for treatment.
Patients with Staphylococcus aureus folliculitis present with yellow pustules confined to the hair follicles. Dicloxacillin is used for treatment.

Explanation
The clinical presentation is suggestive of Chancroid, which is caused by Haernophilus ducreyi. Patients present with a painful ulcer with a purulent base and undermined edges usually associated with suppurative inguinal lymphadenopathy. Azithromycin is used to treat it.
Patients with Candida albicans vaginal infection present with white, non-foul smelling discharge. On examination, the vulva and vagina are erythematous with fissures and even lacerations, as it is pruritic. Oral fluconazole or clotrimazole creams are used to treat it.
Patients with bacterial vaginosis, which is caused by Gardnerella vaginalis present with a malodorous, grayish vaginal discharge. On examination, the vulva and vagina are not inflarnmed. Treatment is with metronidazole.
Patients with Herpes Zoster, which is caused by the Varicella-zoster virus, present with painful vesicles in a unilateral dermatomal distribution. Famciclovir is used for treatment.
Patients with Staphylococcus aureus folliculitis present with yellow pustules confined to the hair follicles. Dicloxacillin is used for treatment.
TREPONEMA PALLIDUM The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, and tertiary). The primary stage classically presents with a single chancre (a firm, **PAINLESS**, non-itchy skin ulceration), secondary syphilis with a diffuse rash which frequently involves the palms of the hands and soles of the feet, latent syphilis with little to no symptoms, and tertiary syphilis with gummas, neurological, or cardiac symptoms. It has, however, been known as "the great imitator" due to its frequent atypical presentations. Diagnosis is usually via blood tests; however, the bacteria can also be visualized under a microscope. Syphilis can be effectively treated with antibiotics, specifically the preferred intramuscular penicillin G (given intravenously for neurosyphilis), or else ceftriaxone, and in those who have a severe penicillin allergy, oral doxycycline or azithromycin.
Syphilis is believed to have infected 12 million people worldwide in 1999, with greater than 90% of cases in the developing world. After decreasing dramatically since the widespread availability of penicillin in the 1940s, rates of infection have increased since the turn of the millennium in many countries, often in combination with human immunodeficiency virus (HIV). This has been attributed partly to unsafe sexual practices among men who have sex with men, increased promiscuity, prostitution, and decreasing use of barrier protection.

Explanation
Psittacosis is also called parrot fever or ornithosis. It is acquired from birds, such as parrots and parakeets, as well as fowl. People at risk include pet shop workers, such as this woman. Psittacosis is caused by Chlamydia psittaci. Symptoms include fever, chills, muscle aches, headache, and a dry cough.
Chlamydiae are small obligate intracellular bacteria. They have an affinity for epithelial cells. Inclusion bodies are seen in cells with chlamydia infections. They are Gram negative and non-motile. Examples include Chlamydia trachomatis, Chiamydia psittaci, and Chlamyclia pneurnoniae. Diseases produced by chlarnydia include psittacosis and trachoma.
Rickettsias are pleonnorphic obligate intracellular organisms. Examples of Rickettsia include Rickettsia rickettsii (the etiologic agent of Rocky Mountain spotted fever), Rickettsia tsutsugamushi (the etiologic agent of Scrub typhus), and Rickettsia prowazekii (the etiologic agent of epidemic typhus fever).
Bacteria in the genus of Mycobacteria are Gram positive bacteria. They are rod-shaped and do not produce spores. Examples include Mycobacteria tuberculosis, Mycobacteria bovis, and Mycobacteria leprae. Diseases produced by mycobacteria include tuberculosis and leprosy.
Spirochetes refer to bacteria in the genus Spirochaeta. Spirochetes are spiral-shaped bacteria. These are motile bacteria. Leptospira. Treponema, and Borrelia are spirochetes. Diseases caused by spirochetes include leptospirosis, syphilis, and relapsing fever.
Numerous pathogens are classified as Gram negative rods. Some examples of microbes that are Gram negative rods are Bacteroides fragilis, Pseudomonas aeruginosa, Salmonella typhi, Escherichia coil, and Kiebsiella pneumoniae.

Explanation
EPIDERMOPHYTON FLOCCOSURN
is a fungus that produces infections of the skin and nails, but not the hair. The growth rate of the organism is moderate with maturity occurring in about 10 days. The surface of the colony has a brownish yellow to olive gray of khaki color. The surface is at first lumpy and sparse, becoming folded in the center and grooved radially, and eventually velvety. Within several weeks fluffy white mycelium covers the colony. The reverse is orange to brownish with a yellow thin border seen at times. Microscopically the hyphae are septate with no microconidia. The macrocoridia (best seen in young cultures) are smooth, occur as thin and thick walled, have a club shape with rounded ends, contain 2-6 cells, and are found singly or in characteristic clusters. In older cultures the macroconidia often transform into chlamydoconidia.
MICROSPORUM CAMIS VAR. CANIS is a fungus and is a cause of scalp and skin infections. The infection is most prevalent in children. Infections in humans are almost always acquired from infected cats or dogs. The organism has a moderate growth rate with maturity occurring within 6-10 days. The surface growth, a Sabouraud dextrose media, is coarsely fluffy with a whitish surface. The peripheral areas of the colonies and closely spaced radial grooves will contain some yellow pigment. Microscopically the organism produces numerous macroconiclia that are long (10-25 x 35-110unn), spindle shaped, rough, and thick walled. These macroconidia taper off to knoblike ends where the rough surface is especially evident. The rnacroconidia will usually contain more than six compartments. Microconidia are few in number and are club shaped and smooth walled and can be seen along the hyphae.
TRICHOPHYTON MENTAGROPHYTES
is a fungus and is a common cause of athlete's foot. It can however invade all parts of the body, including hair and nails. The organism has a moderate growth rate with maturity occurring within 7-10 days. The colonial morphology can vary greatly (the surface may be buff and powdery or white and downy). It may be pinkish or yellowish. The powdery form will exhibit concentric and radial folds. The reverse side is usually brownish tan but it may occur as colorless, yellow, or red. Microscopically the hyphae are septate. Macroconidia measure 4-8 x 20-50um. They are cigar shaped and thin walled with a narrow attachment to the hyphae and contain 1-6 cells. The macroconidia are more commonly seen in young cultures 5-10 days old and can be difficult to find in older cultures. The nnicroconidia are small and tear shaped and clustered on branched conidiophores. Coiled spiral hyphae are often seen.
TRICHOPHYTON TONSURANS
is a fungus and is the most common cause of scalp ringworm in the United States. The organism can also infect the skin and nails. The rate of growth is moderately slow with maturity occurring in 12 days. The colonial morphology is variable with the surface color varying from white, grayish, yellow, brownish, or rose. The surface of the colony can be described as suede-like with the presence of radial and concentric folds. The reverse is usually a reddish brown
color with some of the pigment noticeably diffusing into the surrounding media. The reverse color can at times be yellow or colorless. Microscopically the hyphae are septate and have many variably shaped nnicroconidia lining the sides at a perpendicular angle. The microconiclia are teardrop or clubbed shaped, but may be elongate or enlarge to round "balloon" forms. The macroconidia are rare. They are irregular in form and thick walled. Spiral coils can be seen.
TRICHOPHYTON SCHOENKINI
is a fungus and is the cause of favus. The disease favus is chronic in nature and results in scalp scarring with permanent hair loss. Infections of the nails and skin are possible, though not as commonly encountered. The fungus is a slow grower with maturity occurring within 15 days. The colonial morphology is characteristically whitish, and slightly downy or waxy. The surface is folded or heaped and can be described as yeast-like in
appearance. The reverse of the colony is colorless or yellowish orange to tan in color. The colony is found to grow into the agar. Microscopically the hyphae are septate and irregular in shape with a knobby appearance. Characteristic antler-like branching structures are formed by the subsurface hyphae, which are called "favic chandeliers". Chlamydoconidia are numerous while nnicroconidia are rare and macroconidia are virtually never seen. Because of the initial appearance of the colonies macroscopically and microscopically, this organism can resemble yeast.

Explanation
The microorganism causing vaginitis in the patient is Trichamonas vaginalis, a flagellate protozoan parasite. Trophozoite is the infective form. For Tvaginalis, no cyst form is known. The parasite has 4 anterior flagella
and a 5th flagellum along the undulating membrane. Flagella are the organs of motility. Cilia are absent. Undulating membrane of T.vaginalis is short reaching up to the middle of the body. This is a differentiating feature from other trichornonads of humans in which the undulating membrane extends full length of the parasite. The organism grows best under anaerobic conditions at 35-37°C with an optimal pH 5.5 to 6. Normal acidic pH of 3.8- 4 is detrimental to the growth of T. vaginalis.
The trophozoite cannot survive outside the body for long, so transmission has to be from person to person by close contact. Humans are the only natural hosts of the parasite. T.vaginalis lives mainly in the vagina and cervix in the female and in the anterior urethra of the male. Sexual transmission is the common mode of infection. The parasite divides by longitudinal binary fission. Trichornoniasis is the most common non-viral sexually transmitted disease of worldwide distribution. Infection is most common in sexually active women of reproductive age. The incubation
period ranges from 4 days to 4 weeks. Infection may be asymptomatic or cause acute inflammatory disease of the vagina and cervix. Trichomoniasis is characterized by an increased pH of vagina, brought about by decrease or elimination of Lactobacillus species that constitute normal vaginal flora. Hormones also may play a role in the susceptibility to infection as evidenced by the worsening of symptoms during menstruation. Iron from the menstrual blood is thought to help Trichornanas vagina/is to attach to the squamous epithelium of the genital tract. Complications of the infection include cervical erosion and infertility. In pregnant women infected with the organism, premature labor and low birth weight infants have been observed. Nonsexually transmitted form of the disease may occur in neonates (neonatal trichomoniasis) born to infected mothers. Symptomatic as well as asymptomatic cases have been reported. By causing acute local inflammation of the genital mucosa, T.vaginalis may act as a potential catalyst in the acquisition or transmission of other STDs like HIV and Human Papilloma Virus (HPV), the virus associated with pathogenesis of carcinoma of cervix (Ref:6).
Infection in males is usually mild or asymptomatic. Clinical manifestation of urethritis may simulate non-gonococcal urethritis. Prostatitis, epididymitis, and infertility can occur as complications.
Laboratory diagnostic methods include microscopy, culture, antigen detection tests by enzyme-linked immunosorbant assay (ELISA), and molecular tests based on polyrnerase chain reaction (PCR). Microscopy for motile trichomonas in wet preparation of vaginal discharge should be perFormed within 10-20 minutes of collection to prevent the organisms from losing their viability. Smears stained by Giemsa stain or Acridine orange helps to demonstrate structural details of the parasite (video clips showing motility of Tvaginalis and microscopic appearance of the parasite in Giemsa-stained preparation are accessible in reference 7). Nucleus, flagella, undulating membrane, and axostyle are prorninant structures in stained smears.
Culture is the gold standard and special media like Diamond's medium are used. Growth result is obtained in 2-5 days. Rapid ELISA assay with good sensitivity and specificity for antigen detection is of value in settings without facilities for microscopy. PCR based tests for detection of T.vaginalis in clinical samples using different primers are under development and validation. Self-obtained specimens of vaginal swabs also can be used for the test. PCR test is reported to be of use when shipping of specimens to a reference laboratory is required. Urine and urethral swabs are good clinical samples for diagnosing T. vaginails infection in males.
Incidence of Trichomoniasis in the United States is high. Estimated 8 million new cases occur each year.
Centers for Disease Control and Prevention (CDC) recommends metronidazole 2 gram orally as a single dose for treatment of T.vaginalis infection. Treatment of sexual partners is also recommended. Metronidazole resistant infections have been reported and Tinidazole, a 5-nitroimidazole, is useful for treatment of such cases.