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Abstract

A 38-year-old female presented to the emergency room with persistent fever, lymphadenopathy, numerous erythematous, indurated papules, and nodules on the head, neck, and bilateral upper and lower extremities.  Her history is significant for presumed atypical mycobacterial infection, diagnosed one year ago by skin biopsy and microbiologic cultures. These identified acid-fast bacilli but failed to determine species. She was treated with combination antibiotics and steroids. Upon admission, a punch biopsy of an arm nodule was performed for a clinical suspicion of Sweet syndrome. Histopathologic evaluation revealed collections of epithelioid histiocytes with admixed lymphocytes and neutrophils in a perivascular distribution within the dermis and subcutaneous fat lobules.  These granulomata contained innumerable short acid-fast bacilli. A concurrent lymph node biopsy was also positive. Immunological evaluation revealed lymphopenia and mild hypogammaglobulinemia.  Additional questioning revealed a history of unilateral madarosis and hypoesthesia, which was previously worked up for a primary neurologic condition and attributed to gestational diabetes. This constellation of clinical and laboratory findings was concerning for Hansen’s disease with development of erythema nodosum leprosum (ENL). AFB PCR testing confirmed Mycobacterium leprae.  ENL is a severe inflammatory complication of leprosy resulting from immune complex deposition in the skin. It affects about 50% of patients with lepromatous leprosy and can occur at any stage of multi-drug therapy. This case highlights the histopathologic overlap between atypical mycobacterial infections and erythema nodosum leprosum, along with the importance of correlation between clinical and laboratory findings for definitive diagnosis.