Hyperviscosity syndrome in rheumatoid arthritis.

The course of a patient with rheumatoid hyperviscosity syndrome is described. Manifestations of hyperviscosity included somnolence, circulatory overload, bleeding diathesis and dilated retinal veins. Serum hyperviscosity was associated with marked hypergammaglobulinemia, elevated IgM and IgG serum concentrations, and high titers of rheumatoid factor. High molecular weight IgG-IgM immune complexes shown in the serum were considered responsible for the increased viscosity. An unusual feature of the hyperviscosity, was spurious hyponatremia and a negative anion gap. Plasmapheresis rapidly controlled acute features of hyperviscosity, lowered gamma globulin concentrations and led to normal serum sodium and anion gap. Clinical improvement was maintained with moderate prednisone doses.