MAGニューロパチー

Anti-Myelin-associated Glycoprotein Neuropathy

MAGニューロパチーはMGUSなどのIgM型M蛋白血症を背景に発症する脱髄性ニューロパチーである。緩徐進行性の感覚障害または感覚運動障害と運動失調を呈する。診断はM蛋白とMAG抗体の検出によってなされるが，神経伝導検査では遠位潜時が延長し，腓腹神経病理では電子顕微鏡でwidely spaced myelinが見られる。一般的に免疫療法への反応性は不良であるが，リツキシマブが約半数で有効であり，今後の治療開発が期待される。

Abstract

Anti-myelin-associated glycoprotein (MAG) neuropathy, which occurs secondary to immunoglobulin (Ig)M paraproteinemia such as monoclonal gammopathy of undetermined significance, is characterized by slow progression, sensory or sensorimotor disturbances, and ataxia. The estimated prevalence of this neuropathy in Japan is 0.28 per 100,000 population with male preponderance. This neuropathy is diagnosed based on the detection of M protein and anti-MAG antibodies in patients' serum. Nerve conduction studies show prolonged distal latency, and histopathological evaluation of sural nerve biopsies shows widely spaced myelin on electron microscopy. Usually, immunotherapy, including administration of intravenous Ig and corticosteroids, is ineffective, and rituximab is beneficial in approximately 50% of patients. Novel therapies, such as administration of Bruton's tyrosine kinase inhibitors are expected to benefit patients with the MYD88^L265P mutation.