Axonal loss influences the response to rituximab treatment in neuropathy associated with IgM monoclonal gammopathy with anti-myelin-associated glycoprotein antibody.

Polyneuropathy associated with anti-Myelin-Associated Glycoprotein (MAG) antibody is a well-defined immune-mediated disease that develops in individuals with IgM monoclonal gammopathy. Factors related to response to rituximab treatment in anti-MAG neuropathy have not been clarified so far. We prospectively evaluated the clinical status, immunological changes, and electrophysiological parameters before and 12 months after rituximab treatment in 7 patients with anti-MAG neuropathy. Pathological indices of sural nerve biopsy specimens before rituximab treatment were investigated. Overall, 4 patients improved by more than 5% either clinical scale, expressed according to the Medical Research Council (MRC) sum score or sensory sum score (SSS) 12 months after rituximab treatment. The modified Rankin Scale (mRS) scores improved in 2 patients. With respect to the relationship between the response to rituximab treatment and the clinicopathological findings, short disease duration and preservation of nerve fiber density were significantly related. The immunohistochemical assessment suggested that low-intensity binding of anti-IgM antibody to the myelin sheath may contribute to the degree of response to rituximab treatment. The degree of axonal loss and the deposition of pathogenic autoantibodies in myelinated fibers may determine the therapeutic response to rituximab treatment in anti-MAG neuropathy.