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Diagnosing Histoplasmosis When Limited to the Skin

Clinician's Brief

Infectious Disease

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April 2014

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Histoplasmosis, a deep fungal infection caused by Histoplasma capsulatum, is most common in North, Central, and South America; Africa; India; and Asia. In Europe, the disease has only been reported once: A castrated outdoor cat presented with a one-month history of papules and nodules, some of which were ulcerated and drained a serosanguineous fluid. Cytological examination of exudate was suggestive of a fungal infection, and histologic examination of skin biopsy specimens revealed organisms compatible with H capsulatum var capsulatum. Fungal culture was negative, and diagnosis was confirmed by PCR. There was no evidence of systemic involvement on physical examination, laboratory testing, or imaging. Given that the distribution of the lesions was limited to the skin, treatment consisted of surgical excision of nodules and oral itraconazole at 5 mg/kg q24 for 12 weeks. At 8-month follow up, the cat was healthy with no evidence of recurrence.

Commentary

This exemplified more being missed for not looking than for not knowing. The differential diagnoses for nodular diseases in cats generally include infections, neoplasia, and granulomatous disease. Little evidence suggested that this cat had histoplasmosis, as there were no signs of systemic involvement (eg, weight loss, lethargy, fever, anorexia, interstitial lung disease, anemia). In addition to the disease being limited to the skin, the cat had no travel history. Cytology and histopathology were suspicious, but the diagnosis was confirmed via PCR; it is not uncommon for fungal culture to be negative. A urine H capsulatum antigen test was recently reported to be positive in 17/18 cats with confirmed diagnosis, suggesting this may be a useful diagnostic aid.1 In this case, researchers hypothesized the infection came from an indigenous source in Switzerland. There were no poultry farms in the area where the cat lived, but wetlands with a large bat population were nearby.—Karen A. Moriello, DVM, DACVD

Source

A case in Europe of feline histoplasmosis apparently limited to the skin. Fischer NM, Favrot C, Monod M, et al. VET DERMATOL 24:635-e158, 2013.

1. Clinical evaluation of urine Histoplasma capsulatum antigen measurement in cats with suspected disseminated histoplasmosis. Cook AK, Cunningham LY, Cowell AK, Wheat LJ. J FELINE MED SURG 14:512-515, 2012.

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