Indomethacin-related serum sickness-like illness with IgM lambda cryoparaprotein?

A unique association of a transient IgM lambda monoclonal gammopathy and a serum sickness-like illness, appearing after a short course of indomethacin, is described. The IgM lambda monoclone did cryoprecipitate along with fibronectin in hypotonic medium and disappeared with the resolution of the clinical picture. Emphasis is given to the role of some foreign antigens in the induction of benign monoclones.