Bullous tinea pedis with direct immunofluorescence positivity: when is a positive result not autoimmune bullous disease?

Skin biopsy for direct immunofluorescence (DIF) testing is an essential tool in the diagnosis of blistering diseases. In the majority of cases, positive epidermal immunofluorescent staining is indicative of an autoimmune bullous disease (AIBD). We identified 2 patients with bullous dermatophyte infection diagnosed on hematoxylin- and eosin-stained sections who had positive DIF findings on biopsy of perilesional skin. We subsequently reviewed the literature regarding positive DIF findings in conditions other than AIBD. Other infections, including herpesviridae, scabies, and orf, have rarely been reported to yield positive DIF findings, with positive staining at the dermoepidermal junction. Some genodermatoses and many inflammatory skin diseases, including lichen planus, psoriasis, graft-versus-host disease, among others, may also have DIF findings mimicking those of both intra- and subepidermal AIBD. Although rare, positive DIF results occur in conditions other than AIBD. In many instances, the pathophysiological mechanisms behind immunoreactant deposition in these conditions are poorly understood. Misleading DIF results may lead to delay in correct diagnosis and treatment. Clinicians should be aware of potential alternate sources of positivity when there is lack of clinical correlation with immunofluorescence findings.