Histopathology of a granulomatous lobular panniculitis in acute Q fever: a case report.

Q fever is a zoonotic infection caused by Coxiella burnetii. Two forms of the disease have been described: an acute form with pneumonia, hepatitis or a flu-like syndrome; and a chronic form in which endocarditis is the most frequent clinical expression. We report a 77 year old male with fever and an erythematous nodule on the right leg. Biopsy revealed a granulomatous lobular panniculitis with some granulomas rimmed by an eosinophilic material, giving a "doughnut" or "fibrin-ring" appearance. Q fever serological studies were positive. Cutaneous signs, among them panniculitis, are probably underestimated during the acute phase of the disease, and recognizing different granulomatous patterns may contribute to the diagnosis.