Articles CME Multifocal motor neuropathy improved by IVIg Randomized, double-blind, placebo-controlled study P. Federico, MD, PhD; D.W. Zochodne, MD, FRCPC; A.F. Hahn, MD, FRCPC; W.F. Brown, MD, FRCPC; and T.E. Feasby, MD, FRCPC Article abstract—Objective: To determine the effect of IV immunoglobulin (IVIg) on neurologic function and electrophysi- ologic studies in multifocal motor neuropathy with conduction block (MMN). Background: MMN is characterized by progressive, asymmetric, lower motor neuron weakness and is probably immune-mediated. IVIg treatment has been shown to have beneficial effects in several open-label studies and in one small controlled trial. However, larger random- ized controlled studies are lacking. Methods: The authors recruited 16 patients with MMN. All subjects were given each of two treatments (IVIg [0.4 g/kg/d for 5 consecutive days] or placebo [dextrose or saline]) that were assigned according to a randomized, crossover design under double-blind conditions. Patients were evaluated before and about 28 days after trial treatment for subjective functional improvement, neurologic disability score, grip strength, distal and proximal compound muscle action potential amplitude, and conduction block. Results: Subjective functional improvement with IVIg treatment was rated as dramatic or very good in nine patients, moderate in one, mild in one, and absent in five patients. This improvement was absent after placebo. The neurologic disability score improved by 6.7  3.3 points with IVIg treatment, whereas it decreased by 2.1  3.0 with placebo (p = 0.038). Grip strength on the weaker side was increased by 6.4 1.9 kg with IVIg treatment; it decreased by 1.0  0.8 kg with placebo (p = 0.0021). Conduction block worsened by 12.98  6.52 % with placebo, but improved by 12.68  5.62 % with IVIg treatment (p = 0.037). Conduction block was reversed in five patients with IVIg but not placebo. Conclusion: IVIg improved conduction block as well as subjective and objective clinical measures of function in patients with MMN. NEUROLOGY 2000;55:1256 –1262 Multifocal motor neuropathy with conduction block (MMN) is an uncommon idiopathic syndrome charac- terized by asymmetric lower motor neuron weak- ness, most often starting in the arms in a peripheral nerve distribution. It is slowly progressive, although it may occasionally have a stepwise progression. 1 Re- flexes are usually preserved and sensory involve- ment is absent or minimal. Diagnostic features include evidence of motor conduction block, normal sensory potentials, and, in some patients, elevated immunoglobulin M (IgM) anti-GM1 antibodies. 1 MMN may be immune-mediated. Some patients have elevated anti-GM1 or anti-asialo-GM1 antibody levels (principally IgM). 2-8 Immune therapies have been used to treat MMN. Prednisone and plasma exchange alone were ineffective treatments for MMN, in contrast to their benefit in chronic inflam- matory demyelinating polyradiculopathy. 3,9-13 Oral cyclophosphamide was similarly ineffective. 5 IV cy- clophosphamide, however, may have a modest effect in improving muscle strength but not electrophysi- ologic abnormalities. 3,10,11 A recent open trial of three patients showed improved strength after 6 to12 months of interferon-–1a treatment. 14 Human IVIg has been shown to be effective in improving subjective and objective measures of strength in MMN in nonrandomized, uncontrolled studies. 3,10,11,15-20 Its influence on electrophysiologic abnormalities (principally conduction block) and anti-GM1 antibody levels were variable, with no See also page 1246 From the Department of Clinical Neurosciences (Drs. Federico, Zochodne, and Feasby), University of Calgary, Alberta, Canada; Department of Clinical Neurological Sciences (Dr. Hahn), University of Western Ontario, London, Ontario, Canada; and Department of Neurology (Dr. Brown), New England Medical Center, Tufts University, Boston, MA. Supported by the Bayer-Canadian Red Cross Research and Development Fund and the Muscular Dystrophy Association of Canada. D.W.Z. is a Medical Scholar of the Alberta Heritage Foundation for Medical Research. Received November 29, 1999. Accepted in final form September 12, 2000. Address correspondence and reprint requests to Dr. Thomas E. Feasby, Department of Clinical Neurosciences, Foothills Hospital, Room 1166, 1403 29 Street NW, Calgary, Alberta T2N 2T9, Canada; e-mail: feasby@dcns.ucalgary.ca 1256 Copyright © 2000 by AAN Enterprises, Inc.