Case 20 | Clinical Pathology Unknown Conference

1. Presented by Maryam Shabhikhani, MD and reviewed by Sean Zhang, MD, PhD

Case vignette

An adult patient with no significant past medical history presented for several weeks of swelling and rash of a finger. The patient's social history is notable for work with reptiles and small mammals, with previous reptile bites. The patient had been seen by a primary care physician and received treatment with topical steroids and cephalexin. However, the rash persisted. A punch biopsy was performed which revealed psoriasiform epidermal hyperplasia, subcorneal pustules and perivascular and mixed inflammation. The depth of the mixed dermal inflammation raised concern for Majocchi's granuloma or other infectious process centered in the dermis. However, deeper sections did not demonstrate any underlying follicular epithelium. A PAS stain performed on the histologic sections revealed fungal hypae in the stratum corneum. Fungal culture was positive and showed a fluffy, white surface. See below for macro- and micro- pictures of the organism.

Question: The patient's presentation and laboratory findings are best explained by infection with:

Trichophyton tonsurans

Trichophyton rubrum

Trichophyton mentagrophytes

Microsporum gypseum

Microsporum canis

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