Background
Clinical spectrum of immunoglobulin M (IgM) monoclonal gammopathy varies from IgM monoclonal gammopathy of unknown significance (IgM-MGUS) to hematological malignancies. We evaluated the clinical features, electrophysiological characteristics, and prognosis of patients with peripheral neuropathy associated with IgM monoclonal gammopathy (PN-IgM MG).
Methods
We retrospectively evaluated 25 patients with PN-IgM MG. Peripheral neuropathy was classified as axonal, demyelinating, or undetermined, based on electrophysiological studies. We classified the enrolled patients into the IgM-MGUS and malignancy groups, and compared the clinical and electrophysiological features between the groups.
Results
Fifteen patients had IgM-MGUS and 10 had hematologic malignancies (Waldenström’s macroglobulinemia: two and B-cell non-Hodgkin’s lymphoma: eight). In the electrophysiological evaluation, the nerve conduction study (NCS) criteria for demyelination were met in 86.7% of the IgM-MGUS group and 10.0% of the malignancy group. In particular, the distal latencies of the motor NCS in the IgM-MGUS group were significantly prolonged compared to those in the malignancy group (median, 9.1 ± 5.1 [IgM-MGUS], 4.2 ± 1.3 [malignancy], p = 0.003; ulnar, 5.4 ± 1.9 [IgM-MGUS], 2.9 ± 0.9 [malignancy], p = 0.001; fibular, 9.3 ± 5.1 [IgM-MGUS], 3.8 ± 0.3 [malignancy], p = 0.01; P-posterior tibial, 8.3 ± 5.4 [IgM-MGUS], 4.4 ± 1.0 [malignancy], p = 0.04). Overall treatment responses were significantly worse in the malignancy group than in the IgM-MGUS group (p = 0.004), and the modified Rankin Scale score at the last visit was higher in the malignancy group than in the IgM-MGUS group (2.0 ± 1.1 [IgM-MGUS], 4.2 ± 1.7 [malignancy], p = 0.001), although there was no significant difference at the initial assessment.
Conclusions
The risk of hematological malignancy should be carefully assessed in patients with PN-IgM MG without electrophysiological demyelination features.

Paraproteinemic neuropathy is a heterogeneous set of neuropathies characterized by the presence of homogeneous immunoglobulin in the serum. Most cases are associated with monoclonal gammopathy of undetermined significance. It might also occur in hematologic malignant and nonmalignant conditions. The association between neuropathy and monoclonal gammopathy requires appropriate neurological and hematological investigations. Treatment is mostly based on underlying hematologic disorders. In this review, we provide a clinically practical approach to clinical, laboratory, electrophysiological features and management of patients with paraproteinemic neuropathy.

POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy and skin changes) syndrome is a rare multisystem disorder associated with osteosclerotic myeloma. It is characterized by peripheral polyneuropathy, presence of monoclonal plasma cell proliferative disorder, and one or more of the following features – sclerotic bone lesions, Castleman disease, elevated levels of vascular endothelial growth factor, organomegaly, extravascular volume overload, endocrinopathy, skin changes, papilledema, and thrombocytosis. Extramedullary plasmacytoma (EMP) is a rare plasma cell neoplasm that arises in isolated tissues without bone marrow involvement or systemic characteristics of multiple myeloma. Herein, we report a male patient who was previously diagnosed with EMP and later developed POEMS.

Paraproteinemia is caused by a proliferation of monoclonal plasma cells or B lymphocytes. Approximately 10% of idiopathic neuropathies are associated with paraproteinemia, where a certain paraprotein acts like an antibody targeted at constituents of myelin or axolemma in peripheral nerves. The relationship between paraproteinemia and peripheral neuropathy remains unclear despite this being of interest for a long time. Neurologists frequently find paraproteinemia during laboratory examinations of patients presenting with peripheral neuropathy, especially in the elderly. The possibility of a relationship with paraproteinemia should be considered in cases without an explainable cause. We review the causal association between paraproteinemia and neuropathy as well as clinical, laboratory, and electrophysiologic features, and the treatment options for paraproteinemic neuropathy.

Citations

• A Practical Review of Paraproteinemic Neuropathy
  Joong-Yang Cho
  Korean Journal of Neuromuscular Disorders.2022; 14(2): 23.     CrossRef

The paraproteinemia is a disorder in which a single clone of plasma cells (monoclonal gammopathy) is responsible for the proliferation of monoclonal proteins (M-proteins). Approximately 10% of patients with idiopathic peripheral neuropathy have monoclonal gammopathy. Some M-proteins have the properties of an antibody to the components of peripheral nerve myelin, but the pathophysiological relationship between the neuropathy and the M-protein is often obscure. The relationship between peripheral neuropathy and monoclonal gammopathy requires the appropriate neurological and hematological investigations for precise diagnosis and treatment. In this review, we provide an update on the causal associations between peripheral neuropathy and monoclonal gammopathy as well as characteristics of clinical and electrophysiologic features.