Systemic lupus erythematosus diagnosed during interferon alfa therapy.

We describe a patient who had clinical manifestations of several autoimmune disorders: Sjögren's syndrome, benign hypergammaglobulinemic purpura of Waldenström, and systemic lupus erythematosus (SLE). The SLE was diagnosed during therapy with interferon alfa. Testing for anti-Ro and anti-La antibodies was negative until the serum was diluted to eliminate a possible prozone phenomenon of antibody excess.