Pure Motor Chronic Inflammatory Demyelinating Polyneuropathy: Relationship to Multifocal Motor Neuropathy with Conduction Block (P06.137)

Abstract

Objective: To report two cases of pure motor chronic inflammatory demyelinating polyneuropathy (CIDP), response to therapy, and possible relationship to multifocal motor neuropathy with conduction block (MMN). Background Motor CIDP is a rare variant of classic CIDP that is not well understood in regard to both its pathogenesis and appropriate treatment. The few studies that have been published suggest that unlike classic CIDP, motor CIDP does not respond well to corticosteroids. Design/Methods: Two motor CIDP patients are presented, one of whom has high titers to anti-GM1 antibodies. Results: Patient 1 is a 48 year old woman with a history of CIDP who developed worsening of her strength and diffuse wasting and fasciculations concerning for motor neuron disease. She was found to have an elevated titer of anti-GM1 antibodies of 1:102,400 and a pure motor demyelinating neuropathy with secondary axonal degeneration by electrodiagnosis. The patient failed to respond to weekly IVIG therapy and then worsened with corticosteroids, becoming bed-bound and requiring non-invasive ventilation. Despite weekly rituximab infusions, she continued to declined and was started on monthly plasma exchange and intravenous cyclophosphamide. She can now walk and her anti-GM1 antibody titer has fallen to 1:12,800. Patient 2 is a 56 year old man who presented with a three month history of fasciculations, progressive wasting, and diffuse weakness requiring a wheelchair after failing to respond to single courses of both IVIG and plasma exchange. His electrodiagnostic testing revealed findings similar to the first patient. He was restarted on weekly IVIG and, after 12 courses, finally recovered his ability to walk. Conclusions: Motor CIDP may be more resistant to treatment than classic CIDP. High titers of anti-GM1 antibodies and paradoxical worsening with corticosteroids in some patients could also support a distinct pathogenesis more similar to MMN. Abundant fasciculations seen in this disorder may mistakenly suggest motor neuron disease. Disclosure: Dr. Thyerlei has nothing to disclose. Dr. Weiss has received personal compensation for activities with Walgreens, CSL Behring and Talecris Biotherapeutics as a consultant and/or speaker.