Erythrocyte sensitization with monomeric IgM in a patient with hemolytic anemia.

An automated antiglobulin test showed that erythrocytes of a patient with an acute episode of Coombs-negative hemolytic anemia were strongly sensitized with nonagglutinating IgM molecules. The bound antibodies, after elution from red blood cell stroma, were found to be monomeric IgM, since they migrated with IgG molecules on an agarose column, although they were proved to be immunoglobulin M, not G, by a sensitive hemagglutination inhibition assay. The hemolysis subsided with steroid therapy, but ANA increased to a titer greater than 1,024 (with peripheral pattern) without other laboratory evidence of systemic lupus erythematosus. In addition, the patient demonstrated photosensitivity and nonscarring alopecia. We consider that this appearance of erythrocyte autoantibodies consisting of monomeric IgM was a symptom of atypical SLE.