Intraneuronal accumulation of myeloma proteins.

We studied a patient with multiple myeloma who had immunologically identified myeloma light chain proteins within neurons projecting beyond the blood-brain barrier, but not within intrinsic neurons of the spinal cord, brain stem, and cerebral cortex. There was a possibility that these myeloma light chain proteins or their immunologically recognizable fragments were transported intra-axonally by human peripheral nerves. Myeloma light chain proteins were also identified within cerebellar Purkinje's neurons. This labeling may have been secondary to transport from cerebrospinal fluid.