Clinical Exposures: Canine dermatophyte infection
Dec 01, 2007
A 3-month-old intact male boxer was presented for a preadoption evaluation at the Foster Hospital for Small Animals at Tufts University after being rescued in North Carolina. The physical examination results were unremarkable except for mild, patchy alopecia on the frontal aspect of the head and a 3-x-2-cm dermal, nodular lesion on the left lateral thigh. These skin lesions were nonpruritic and nonulcerated.
CYTOLOGIC EXAMINATION FINDINGS
Demodex and Sarcoptes species mites were not found on microscopic examination of samples obtained by deep skin scraping of the alopecic area on the head. Cytologic examination of the skin scraping revealed low numbers of erythrocytes, multiple broken hair shafts and anucleate squamous epithelial cells, and small to moderate amounts of keratin debris.Samples from the thigh lesion were obtained by fine-needle aspiration, and the slides were stained with Wright's-Giemsa. Cytologic examination revealed moderate numbers of erythrocytes and intact nucleated cells. Moderate numbers of inflammatory cells were found, with a predominance of nondegenerate neutrophils and lesser numbers of activated macrophages. A few small lymphocytes and eosinophils were also noted. Some macrophages contained phagocytosed cellular debris and rare hematoidin crystals.
The samples from the thigh lesion also contained a small population of superficial squamous epithelial cells—both individual cells and variably sized aggregates—mixed with varying amounts of keratin debris. A few squamous epithelial cells contained cytoplasmic melanin granules, and others had multiple adherent bacteria.
The presumptive diagnosis was mixed inflammation secondary to infection with a nonpigmented fungus. Differential diagnoses for mycotic infections that form hyphal elements in tissues include dermatophytosis (e.g. Microsporum species, Trichophyton mentagrophytes) and infection with Aspergillus or Penicillium species or other nonpigmented fungi (e.g. Acremonium, Fusarium, Geotrichum, Paecilomyces, Pseudallescheria, and Scedosporium species). Zygomycosis (e.g. Basidiobolus and Conidiobolus species) and pythiosis were also considered because of the puppy's geographic origin.1
HISTOLOGIC EXAMINATION AND DEFINITIVE DIAGNOSIS
Granulomatous folliculitis and furunculosis with intralesional dermatophyte arthrospores and hyphae were diagnosed. The fungal elements were consistent with dermatophytosis, specifically Microsporum canis infection. The nodular form of dermatophytosis was suspected, but fungal culture to confirm the genus and species of the dermatophyte was not done.