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

Step 1: Note the key histology. The combination of foamy (lipid-laden) histiocytes plus a neutrophilic infiltrate in the dermis is the hallmark of erythema nodosum leprosum (type 2 lepra reaction).
Step 2: Explain the foamy histiocytes. In lepromatous leprosy macrophages are stuffed with degenerating Mycobacterium leprae and lipid, producing foam cells (Virchow lepra cells); during the type 2 reaction neutrophils are recruited into this background.
Step 3: Correlate with the clinical picture. Fever with crops of tender nodules on the limbs in a young patient is the classic acute systemic presentation of erythema nodosum leprosum.
Step 4: Exclude the others. Plain erythema nodosum shows septal panniculitis without foamy histiocytes; Sweet's syndrome shows a dense dermal neutrophilic infiltrate but no foam cells; Rosai-Dorfman disease shows histiocytes with emperipolesis, not neutrophils.
Conclusion: The foam cells plus neutrophils point to erythema nodosum leprosum. The printed key (D, erythema nodosum) is medically incorrect; the medically correct option is C, erythema nodosum leprosum.