[Rapid improvement by rituximab treatment in a case of demyelinating polyneuropathy with anti-myelin-associated glycoprotein antibody].

Polyneuropathy associated with antibodies directed against myelin-associated glycoprotein (MAG) is a chronic symmetric sensorimotor demyelinating neuropathy caused by monoclonal IgM against MAG (anti-MAG neuropathy). Intravenous immunoglobulin therapy (IVIg) has been partially successful in patients with anti-MAG neuropathy. A placebo-controlled trial of rituximab in patients with anti-MAG neuropathy has been reported. We report rapid improvement in a patient with anti-MAG neuropathy using rituximab. A 58-year-old man presented with abnormal sensation, weakness of the limbs, and unsteadiness. He was previously diagnosed with chronic inflammatory demyelinating neuropathy and was treated with steroid pulse therapy and IVIg. However, these treatments were not effective. On examination at our hospital, he showed areflexia in all limbs, mild weakness in distal portions of upper and lower extremities, sensory ataxia, and hypesthesia/hypalgesia except for his face. He showed high serum IgM levels (323mg/dl). He did not show M protein on immunoelectrophoresis; however, anti-MAG and anti-sulfoglucuronyl paragloboside (SGPG) antibodies were detected by immunoblot and enzyme-linked immunosorbent assay, respectively. He was diagnosed with anti MAG neuropathy and was administered four cycles of intravenous rituximab at a dose of 375mg/m(2)/week. After the first cycle of rituximab administration, he showed improvement in two-point discrimination of middle fingers (10/13 before therapy to 7/7mm after administration). Two-point discrimination and vibration markedly improved after four cycles of rituximab administration. Romberg sign became negative after 7 months. Anti-SGPG antibody titers reduced from 0.554 before rituximab administration to 0.307 (OD) at 1,600 dilution, 4 months after administration. We concluded that rituximab was effective for the treatment of anti-MAG neuropathy. We suggested that rapid and long-term improvement in our patient might be caused not only by preventing the formation of new antibody-secreting cells and antibody-titer reduction but also affecting the balance of proinflammatory cytokines and regulatory cytokines production.