FDG PET/CT showing erythema nodosum associated with tuberculous lymphadenitis.

Erythema nodosum (EN) is histopathologically an acute septal panniculitis of subcutaneous adipose lobule. It can be either idiopathic or secondary to various underlying conditions. A female patient with EN underwent FDG PET/CT to search underlying cause. The images showed enlarged lymph nodes in the mediastinum with moderately elevated FDG uptake and multifocal increased FDG uptake over her lower extremities. The patient's condition was subsequently diagnosed with EN associated with mediastinal tuberculous lymphadenitis based on skin biopsy, tuberculin skin test, and treatment response.