Erythema multiforme ID reaction in atypical dermatophytosis: a case report

Erythema multiforme (EM) is an uncommon mucocutaneous disorder, characterized by widespread erythematous-oedematous targetoid lesions, considered as a reaction pattern to many different stimuli.

Presentation is made of a classical EM eruption concomitant to an inflammatory, atypical dermatophytosis of the ala nasi, observed in a 37-year-old male at the Dermatology Department of Cagliari, Italy.

Laboratory investigations revealed normal complete blood count and biochemistry profile. A direct microscopic examination with 20% potassium hydroxide of the nasal skin scales and of the vibrissae indicated the presence of dermatophyte hyphae and spores invading the rhinothrix. Culture confirmed a Trycophyton mentagrophytes infection. Specific determination of antiviral immunity in the blood (TORCH) was negative for recent infections, while the cell-mediated response, investigated with a delayed skin multitest, showed a marked positivity for the tricophyton antigen. Systemic therapy with terbinafine (250 mg/day) led to complete clinical and mycological recovery of the atypical ringworm in 30 days. Multiforme lesions rapidly improved and completely disappeared in 7 days.

ID reaction to a distant focus of dermatophyte infection very rarely presents as EM. The presented case fits all the essential criteria required for the diagnosis of an ID reaction. The atypical clinical presentation of the ringworm infection, with marked involvement of the intranasal hairs, seems to have induced an inflammatory allergic response, similar to that evoked by sycosis.