Science News: Pure Motor Onset and IgM-Gammopathy Occurrence in Multifocal Acquired Demyelinating Sensory and Motor Neuropathy

Submitted by: Niranjan N. Singh, MD, DM
Edited by: Francisco Gomez, MD

Beecher G, Shelly S, P. Dyck PJB, et al. Pure motor onset and IgM-gammopathy occurrence in multifocal acquired demyelinating sensory and motor neuropathy. Klein Neurology. Oct 2021;97(14):e1392-e1403.

Summary: This study investigates patients with multifocal acquired demyelinating sensory and motor (MADSAM) neuropathy with and without monoclonal gammopathy of uncertain significance (MGUS). Of 76 patients with MADSAM, 53% had pure motor, 16% pure sensory, 30% sensory-motor and 1% cranial. Motor onset patients were initially diagnosed with multifocal motor neuropathy (MMN). MGUS occurred in 25% (89% IgM) associating with ganglioside autoantibodies. Median time to sensory involvement in motor onset patients was 18 months. Subsequent sensory findings were in the same territory in 35% patients. Brachial and lumbosacral MRI showed hypertrophy and increased T2 signal in 84-87% patients. Most patients required ongoing immunotherapy, patients with MGUS required dual agents.
 
Initial presentation of MMN and MADSAM may be similar in 50% patients. Long-term follow-up with clinical electrophysiology and nerve pathology helps to distinguish motor onset MADSAM from MMN. MADSAM has better prognosis compared to MMN and better response to treatment. Patients with concomitant MGUS required dual immunotherapy. The study also reveals that clinical, electrophysiologic and histopathology findings in MADSAM with and without MGUS were similar.
 
Comments: Pure motor onset demyelinating neuropathy and MGUS may turn out to be either MMN or MADSAM, two different pathologic entities and show different responses to immunomodulation and different prognosis. Neuromuscular and electromyography specialists commonly see them and knowledge regarding the prognosis and long-term follow-up cannot be emphasized.
 
Articles of Similar Interest:
Mezaki T, Kaji R, Kimura J. Multifocal motor neuropathy and Lewis Sumner syndrome: a clinical spectrum. Muscle & Nerve. 1999 Dec;22(12):1739-40.
 
Martinez-Thompson JM, Snyder MR, Ettore M, et al. Composite ganglioside autoantibodies and immune treatment response in MMN and MADSAM. Muscle & Nerve. 2018 Jun;57(6):1000-1005.