Neuropathy and paraproteins: review of a complex association

Abstract

Coexistence of neuropathy and monoclonal gammopathy represents a common but complex problem in clinical practice. This association is here reviewed considering latest available literature. The association is not infrequent, and various possible syndromes need to be distinguished. However, coincidental co-occurrence also needs to be recognized. The monoclonal gammopathy may be a 'monoclonal gammopathy of uncertain significance' (MGUS) or occur in a context of malignancy such as multiple myeloma or Waldenström's macroglobulinaemia. IgM paraproteins can bind to myelin-associated glycoprotein (MAG) in peripheral nerve. In this case, the paraprotein is directly linked to the neuropathy, causing a specific phenotype. One randomized controlled trial of this ('Anti-MAG') neuropathy showed possible moderate effect of rituximab on disability. Results of another trial are awaited. IgM/G/A paraproteins can be associated with a polyneuropathy indistinguishable from chronic inflammatory demyelinating polyneuropathy. Axonal neuropathies may coexist with IgM/G/A MGUS. There is insufficient evidence about causality or effective treatment in such cases. Pain/dysautonomia with an axonal neuropathy and serum paraprotein raises the possibility of amyloidosis. Specific haematological treatment is required for malignant disorders, although caution is required with neurotoxic agents. Polyneuropathy, organomegaly, endocrinopathy, M-protein, skin changes syndrome and chronic ataxic neuropathy with ophthalmoplegia, M-protein, cold agglutinins and disialosyl antibodies represent rare separate entities for which evidence-based treatment options are still lacking. The association of monoclonal gammopathy and neuropathy requires the appropriate neurological/haematological investigations for a precise diagnosis. Causality is only established in few cases. Adequate management ideally requires joint neurological/haematological input for diagnosis, monitoring and treatment.