Abstract & Commentary
Source: Van den Berg-Vos RM, et al. Multifocal motor neuropathy: Long-term clinical and electrophysiological assessment of intravenous immunoglobulin maintenance treatment. Brain. 2002;125:1875-1886.
Eleven patients with multifocal motor neuropathy with conduction block (MMNCB), treated with intravenous immunoglobulin (IVIG) for at least 4 years, were followed over a 4-8-year period to determine the long-term benefits of IVIG with regards to muscle strength and electrophysiologic parameters. Diagnosis was based on the presence of asymmetric, predominantly arm weakness, with electrical evidence of motor conduction block in at least one site. Initial treatment for all patients comprised 5 days of IVIG (0.4 g/kg/d) followed by 1 infusion weekly for a year. Subsequent infusion frequency was determined by patient’s course and ranged from one infusion every 1-7 weeks at an average dose of 7-48 g/wk. Hand-held dynamometry and Medical Research Council (MRC) grading of muscle strength were used to assess progress. Electrodiagnostic studies were performed prior to treatment and annually thereafter. Disability was graded using subscales of the Guy’s Neurological Disability Scale (Mult Scler. 1999;5:223-233). Statistical analysis included paired t-tests and Wilcoxon’s matched pairs test.
Mean MRC sum scores, assessing the strength of 20 muscles, 5 in each arm and leg, significantly improved (P < 0.001) in all patients following the first course of IVIG, declined slightly but significantly (P < 0.01) during maintenance, yet remained significantly higher (P < 0.001) at last follow-up compared to pretreatment. Disability scores improved in 7 patients and remained unchanged in 4 (P < 0.02). Conduction block and distal compound motor action potential amplitudes were not significantly changed in 36 of 66 nerves studied. Where electrodiagnostic improvement was observed, it correlated significantly with the presence of pretreatment conduction block, rather than axonal loss. IVIG maintenance therapy does not induce remission in MMNCB, but strength and disability are improved by mechanisms that enhance remyelination and reinnervation. The frequency of infusions remains individualized.
Commentary
Does the presence of definite or probable conduction block determine clinical presentation, immunological findings, or response to IVIG in multifocal motor neuropathy (MMN)? Among 23 MMN patients, 14 demonstrated definite or probable conduction block in at least one motor nerve (based on American Association of Electrodiagnostic Medicine criteria), 6 had possible conduction block (10% less conduction block than required by above criteria), and 3 showed no conduction block. Age at disease onset, extent and severity of weakness, disability, and frequency of antiganglioside antibodies did not differ between patients with possible conduction block as compared to those with definite or probable conduction block. Response to IVIG treatment, however, was less likely in the possible conduction block group (67% vs 86%). Only 1 (33%) patient without conduction block improved with IVIG (J Neurol Neurosurg Psychiatry. 2002;72:761-766). Patients with suspected MMN who electrodiagnostically demonstrate possible conduction block should be treated as those with definite conduction block. Those without conduction block are unlikely to respond. —Michael Rubin
Dr. Rubin, Professor of Clinical Neurology, New York Presbyterian Hospital-Cornell Campus, is Assistant Editor of Neurology Alert.