Mycoplasma pneumoniae infection-induced erythema nodosum, anaphylactoid purpura, and acute urticaria in 3 people in a single family.

Mycoplasma pneumoniae infection is one of the most common etiologic agents of respiratory tract diseases. Although the respiratory symptoms of this infection commonly are mild, it often is accompanied by various extrapulmonary complications including arthritis and cutaneous manifestations. We report 3 patients with M pneumoniae infection in a single family who revealed erythema nodosum, anaphylactoid purpura, and acute urticaria, respectively. We discuss the similarity between these cutaneous manifestations caused by this infection and those caused by viral infections, and the responsible factors for producing different cutaneous lesions by a single infectious agent in people with common genetic background. Age-related variations in cutaneous manifestations of M pneumoniae infections can be attributed to the immaturity of the adaptive immunity of a host, as has been suggested in viral infections.