Monoclonal IgM immunoglobulinemia in psoriatic arthritis.

Serum protein electrophoresis in a 61-year-old woman with psoriasis and psoriatic arthritis showed a monoclonal spike that was identified as IgM-kappa monoclonal immunoglobulinemia by immunodiffusion and immunoelectrophoresis. There was no clinical evidence of myeloma, Waldenström macroglobulinemia, or lymphoma, and the M component has not changed over a three-year observation period. This unusual occurrence may represent another disease entity that may be associated with nonmyelomatous monoclonal immunoglobulinemia.