UPMC Dermatopathology "Case of the Month" Presentations
UPP - Department of Dermatology, Dermatopathology Unit
Case Authors: Angela Sanfilippo MD., Matthew Zirwas MD., Drazen Jukic MD
APRIL 2005 CASE OF THE MONTH
DISCUSSION & DIAGNOSIS
Diagnosis
Bullous Dermatomycosis
Discussion
This case represents an interesting example of a clinical picture that was not suggestive of the final diagnosis. The patient’s clinical findings were very consistent with varicella zoster virus or a “dewdrops on a rose petal” appearance, however, the patient reported a previous history of varicella zoster as a child. Bullous dermatomycoses are often misdiagnosed as allergic contact dermatitis, or when found on the hands or feet, as dishydrotic eczema. The fact that the patient’s rash resolved with Diflucan and ketoconazole supports the diagnosis of bullous dermatomycosis.
Dermatomycosis refers to any fungal infection of the skin and may be caused by dermatophytes, yeast, or other fungi. The dermatophytes consist of three genera of fungi: Epidermophyton, Trichophyton, and Microsporum; these are capable of colonizing keratinized tissue such as the stratum corneum, hair, and nails. The dermatophytes are grouped according to their natural reservoir: anthropophilic, zoophilic, and geophilic (human, animals, and soil.) Anthropophilic fungi tend to produce the least vigorous host response and zoophilic fungi the greatest. Tinea corporis can be caused by any dermatophyte, however, the most common causes are Trichophyton mentagrophytes, Trichophyton rubrum, and Microsporum Canis. Bullous tinea corporis presents as spongiotic or subcorneal vesicles and pustules which may be herpetiform and is typically caused by T. rubrum in contrast to bullous tinea pedis which is most commonly caused by T. mentagrophytes. M. canis less commonly causes a bullous tinea corporis and manifests as annular lesions with a raised papulovesicular border and central clearing. Diagnostic procedures are typically direct microscopy of potassium hydroxide (KOH) preparations, fungal cultures, and biopsy.
Pathological findings can vary according to the clinical variant but usually include red hyphae within the stratum corneum on PAS stain; fungi can also manifest as arthrospores, yeast forms, or pseudohyphae. Hyphae grow by branching and may form matlike structures called mycelia. Hyphae are basophilic on hemotoxylin and eosin and stain black with methenamine silver. The fungal polysaccharides are diastase resistant, unlike glycogen, and this can be useful in distinguishing glycogen granules from fungal spores. There may be a mixed dermal inflammatory infiltrate although organisms do not typically extend into the dermis unless there is follicular rupture. The intensity of the tissue reaction can range from almost undetectable to a very exuberant or chronic spongiotic-psoriasiform pattern.
Treatment consists of topical or systemic antifungals.
1. El-Segini Y, Schill WB, Weyers W. Case report. Bullous tinea pedis in an elderly man. Mycoses. 2002 Nov;45(9-10): 428.
2. Katoh T, Maruyama R, Nishioka K, Sano T. Tinea corporis due to Microsporum canis from an asymptomatic dog. J Dermatol. 1991 Jun;18(6):356-9.