In a small but significant proportion of cases of "idiopathic" erythema nodosum, bilateral enlargement of the lymph nodes of the pulmonary roots is demonstrable roentgenologically. A sizable nondermatologic literature attests to the recognition of this phenomenon, which is entirely benign, invariably self-limited, and ordinarily unaccompanied by symptoms of intrathoracic disease. The interest focused on the pulmonary finding is intensified by the observation that, as a rule, noteworthy enlargement of other groups of lymph nodes does not concomitantly occur. We wish to recall this mediastinal abnormality to the notice of dermatologists, who are often the sole physicians responsible for the diagnosis and care of patients with erythema nodosum.
Conventionally, erythema nodosum is classified into two types: one in which the cutaneous lesions appear as a reaction to an antecedent or concurrent microbial illness, such as infections of the upper respiratory tract, tuberculosis, coccidioidomycosis, and others (sarcoidosis may arbitrarily be included here),