Myelomatosis and the hyperviscosity syndrome.

Eleven patients are described in whom myelomatosis was complicated by the laboratory and clinical features of the hyperviscosity syndrome (HVS). The myeloma type was IgA in nine and IgG3 in two. In those patients with IgA myeloma the HVS was related to the presence of high molecular weight complexes in the serum. Remission of clinical features was obtained in all patients by plasma exchange. Clinical improvement coincided with reduction of whole blood viscosity and in those patients with IgA myeloma, with a parallel reduction of the high molecular weight complexes. The relationship between the IgA complexes and blood viscosity has been examined by physicochemical analysis of purified IgA monomer and polymers and evidence is presented to show that the IgA polymer has a higher intrinsic viscosity and axial ratio than the larger IgM molecule. The significance of these observations is discussed.