Brucellosis with erythema nodosum-like manifestations diagnosed by isolated positivity of the ELISA test for anti-Brucella IgM.

Brucellosis is endemic in the Mediterranean area. In spite of the false negative results, the standard agglutination test remains the routine test for the diagnosis of brucellosis in southern Italy. We present a case of a patient with undulant fever and erythema nodosum-like skin lesions, with negative serum agglutination test, but isolated positivity of the ELISA test for anti-Brucella IgM. A diagnosis of brucellosis for this patient was supported by the anamnestic and clinical data, and by the response to therapy. This case and a review of the literature urge us to consider the ELISA test indispensable for the serological diagnosis of brucellosis.