Neuropathy with anti-myelin-associated glycoprotein antibodies: update on diagnosis, pathophysiology and management

Antimyelin-associated glycoprotein (MAG) neuropathy is a rare autoimmune demyelinating peripheral neuropathy caused by IgM autoantibodies targeting MAG. The typical presentation is that of a slowly progressive, distal, length-dependent, predominantly sensory, sometimes ataxic neuropathy, frequently accompanied by upper limb tremor. Distal motor weakness may subsequently occur. The clinical presentation may vary and rarely be consistent with that of typical chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), as well as have an aggressive and rapidly disabling course. The diagnosis of anti-MAG neuropathy is based on the detection of anti-MAG antibodies through ELISA or western blot analysis, primarily in presence of an IgM monoclonal gammopathy. Anti-MAG neuropathy may occur without or with haematological malignancy. Electrophysiology is characteristic of a predominantly distal demyelinating neuropathy. Intravenous immunoglobulins and plasma exchange have unproven benefits, but may provide short-term effects. Cytotoxic therapies are commonly used, although without an evidence base. Rituximab, an anti-B-cell monoclonal antibody was studied in two randomised controlled trials, neither of which achieved their primary outcome. However, a meta-analysis of these two studies demonstrated improvement of disability at 8-12 months. A recent trial with lenalidomide was interrupted prematurely due to a high rate of venous thromboembolism. There are currently two ongoing trials with Bruton's tyrosine kinase inhibitors. Symptom control is otherwise frequently needed. Outcome measures used for other inflammatory neuropathies present limitations in anti-MAG neuropathy. International registries such as the planned IMAGiNe study may, in future, provide answers to the many remaining questions.