Erythema Nodosum versus Erythema Induratum: A Crucial Distinction Enabling Recognition of Occult Tuberculosis.

Erythema induratum, previously uncommon, is appearing more frequently coincident with the recrudescence of tuberculosis. It is a type of panniculitis often confused clinically with erythema nodosum. We report two patients who were both initially believed to have erythema nodosum and a multisystem disorder. However, in each case, the lesions appeared atypical due to suppuration or distribution of the lesions. This led to skin biopsies, which showed the presence of erythema induratum and excluded the panniculitis of erythema nodosum or leukocytoclastic vasculitis. This lesion heightened our suspicion of the presence of tuberculosis, which was subsequently confirmed by culture and/or clinical response.This experience suggests that patients with an atypical presentation of erythema nodosum should have a skin biopsy to exclude a diagnosis of erythema induratum.