Question

A young male presented with a history of fever and a nodule in the leg. Histopathology of the nodule revealed foamy histiocytes and a neutrophilic infiltrate in the dermis. The most probable diagnosis is:

• A. Sweet's syndrome
• B. Rosai-Dorfman disease
• C. Erythema nodosum leprosum
• D. Erythema nodosum

Hint:

Foamy histiocytes plus neutrophils equals a type 2 lepra reaction, not plain erythema nodosum.

Answer 1

The Correct Option is C

Let the microscope drive the answer. Two features must be explained together: foamy histiocytes and a sheet of neutrophils sitting in the dermis. Foamy histiocytes are macrophages bloated with lipid and broken-down bacilli, the so-called lepra or Virchow cells that characterise lepromatous leprosy. When such a patient develops fever and crops of painful nodules, an immune complex driven type 2 lepra reaction has set in, and this reaction floods the lepromatous background with neutrophils. That exact pairing of foam cells with neutrophils defines erythema nodosum leprosum. Ordinary erythema nodosum cannot be the answer because its biopsy shows inflammation confined to the fat septa with no foamy histiocytes at all. Sweet's syndrome does deliver a heavy dermal neutrophil load but lacks the foam cells, and Rosai-Dorfman disease is recognised by large histiocytes engulfing intact lymphocytes (emperipolesis) rather than by neutrophils. Hence the printed key of plain erythema nodosum is wrong, and the histology points squarely to the leprosy reaction.\[\boxed{\text{Erythema nodosum leprosum}}\]