Erythema induratum, a classic case of a tuberculid reaction

A 36yo construction worker from Pakistan presented with a ten week history of painful, smooth, poorly defined red nodules to his lower legs and pustular lesions to his upper thighs, with associated fatigue and night sweats.
He had significantly raised inflammatory markers with an ESR of 46 and CRP of 148. Histopathology revealed a large blood vessel undergoing destruction with a florid granulomatous infiltrate in the superficial subcutis. The lumen of the vessel was filled with necrotic inflammatory debris. The septa in the subcutis were thickened by fibrosis and a mixed lobular and septal inflammatory infiltrate of lymphocytes and neutrophils was present. These findings were consistent for erythema induratum (nodular vasculitis).
A tuberculosis screen was performed revealing a strongly positive Mantoux test at 21mm. A chest CT revealed prominent aorto-pulmonary and left hilar lymphadenopathy with a 4.8mm semi-solid nodule in the left upper lobe. Anti-tuberculosis medications were started with an improvement in skin lesions and systemic symptoms.
Erythema induratum is a tuberculid reaction, presenting with tender erythematous to violaceous nodules and plaques on the lower legs. Unlike erythema nodosum, it may ulcerate and has a predisposition for the posterior lower legs.1 It is an uncommon condition but, as demonstrated in this case, is highly important to consider in patients who are from or have visited tuberculosis endemic areas.
1. Patterson J. Panniculitis. In Bolognia J, Jorizzo J, Schaffer J. Dermatology. Third Edition. 2012, Elsevier

Dr. Ryan Toholka