Amoxicillin-induced linear IgA bullous dermatosis mimicking erythema multiforme: a case report

A 77-year-old man presented with a cutaneous rash of 3 days' duration. Seven days before onset, the patient reported a bronchopulmonary infection treated with amoxicillin. Physical examination revealed multiforme cutaneous lesions, involving the armpits, pubis, genitals and lower back. In the lower back area, lesions were erythematous, purplish targetoid-like with multiple concentric circles. In places, bullae and postblistering erosions could be seen. In places, a 'string of pearls' pattern could be observed. Nikolsky sign was negative. Herpes simplex virus polymerase chain reaction (PCR) on mucosal erosions was negative. Multiplex nasopharyngeal PCR was negative for influenza virus, COVID-19 and <i>Mycoplasma pneumoniae</i>. Histopathological examination revealed spontaneous subepithelial cleavage with neutrophilic -microabscesses. Direct immunofluorescence showed linear IgA deposition at the dermal-epidermal junction, confirming the diagnosis of linear IgA bullous dermatosis. Skin lesions were treated with topical clobetasol propionate cream and oral mucosa with corticosteroid mouth rinses. The disease course was marked by complete remission 7 days after amoxicillin discontinuation. There was no relapse after 4 months of follow-up.