Paraproteins in the spinal fluid of patients with paraproteinemic polyneuropathies.

High-resolution agarose gel electrophoresis, combined with immunofixation electrophoresis, was used to detect and identify immunoglobulins in the cerebrospinal fluid of six patients with paraproteinemic polyneuropathy. In four patients with serum IgM kappa monoclonal protein, we found a discrete band in the cerebrospinal fluid identified also as IgM kappa; one patient with serum IgG kappa had an IgG kappa cerebrospinal fluid band, and one patient with serum IgA kappa had an IgA kappa monoclonal band in the cerebrospinal fluid. The permeability of the blood-cerebrospinal fluid barrier was increased 3 to 10 times in all these patients. The findings indicate that in patients with paraproteinemic polyneuropathy, the increased permeability of the blood-cerebrospinal fluid barrier results in influx of serum proteins into the cerebrospinal fluid, including high-molecular-weight IgM. Because monoclonal IgM, unlike monoclonal IgG and IgA, is not found in the cerebrospinal fluid of neurologically intact patients, its presence in the cerebrospinal fluid of patients with paraproteinemias should lead the physician to suspect neurological involvement and can be of diagnostic value.