Make the Diagnosis

Make the Diagnosis - April 2017

This case and photo are courtesy of Jessica Cervantes, University of Miami Miller School of Medicine, and Dr. Bilu Martin.

A 35-year-old male with no significant past medical history presented with the chief complaint of occasional malodorous “crust in his underarms.” He used no prior treatments, and he did report axillary hyperhidrosis.

What's your diagnosis?​

Axillary granular parakeratosis

Tinea corporis

Trichomycosis axillaris

Trichomycosis axillaris

Trichomycosis axillaris (TA) is a bacterial infection of the genus Corynebacterium that affects hairs in the axilla. Predisposing factors include poor local hygiene, hyperhidrosis, obesity, and warm, humid climates. Gram-positive diphtheroids, classically Corynebacterium tenuis , mix with sweat on hair shafts and subsequently produce a cementing material. In the majority of cases, bacterial infection causes keratin damage to the hair shaft with sparing of the cortex. However, recent cases have reported significant invasion of the hair cortex by bacterial structures.

A presents as malodorous, diaphoretic armpits without other apparent symptoms. Bacterial metabolism of testosterone in the apocrine sweat results in production of compounds that yield an acidic odor. Physical examination reveals small amounts of brown-to-yellow concretions adhered to the central part of the hair shaft. Rarely, red or black nodules can also be found. These concretions give a thickened and beaded appearance to the affected hairs.

TA is often a clinical diagnosis. Histopathology reveals a discontinuous thick-layer coating of bacterial structures adhered to the hair shafts. Periodic acid–Schiff, gram, and Grocott silver stains are all positive. Examination of hairs with 20% hydrogen peroxide solution can provide a microscopic diagnosis. Wood lamp examination produces a weak, yellow fluorescence, and potassium hydroxide test demonstrates yellowish material of minimal translucency surrounding the hair cortex.

Complete resolution can be achieved by shaving off all the axillary hairs. It is imperative to maintain good hygiene and keep the area dry and clean. To prevent recurrence, topical benzoyl peroxide or topical antibiotics such as erythromycin and clindamycin can be applied. If axillary hyperhidrosis is concurrently present, aluminum chloride hexahydrate solution can decrease sweating and reduce the risk of bacterial regrowth. Injections of botulinum toxin can be used to treat the hyperhidrosis as well.

This patient responded well to topical erythromycin lotion.

This case and photo are courtesy of Jessica Cervantes, University of Miami Miller School of Medicine, and Dr. Bilu Martin.

Donna Bilu Martin, MD, is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at To submit a case for possible publication, send an email to [email protected].

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