Polyclonal gammopathy with marked increase in serum viscosity.

A 45-year-old man with polyclonal hypergammaglobulinemia (gamma globulins, 102 g/L) had a serum relative viscosity of 13 nu but did not manifest clinical signs of hyperviscosity syndrome (e.g., retinopathy, bleeding diathesis, and neurological alterations), except for fatigue and anorexia. In contrast with other patients with polyclonal hyperviscosity reported so far, this patient did not have detectable rheumatoid factor in serum. Analytical ultracentrifugation of his serum showed aggregates of polyclonal IgG3 of various sizes (between 10 and 36 S). The serum also contained immune complex-like material, as demonstrated by the Raji cell immunoradiometric assay and the C1q solid-phase enzyme immunoassay.