Erythema induratum - a hypersensitivity reaction to Mycobacterium tuberculosis.

Erythema induratum (also known as Bazin disease, tuberculosum, tuberculosis cutis indurativa and nodose tuberculid) is a rare condition that produces painful, firm, and sometimes ulcerated nodules on the lower legs. Distinctive and diagnostic histopathology comprises a septolobular panniculitis, necrosis, granulomatous inflammation and vasculitis.