The clinical and electrophysiological features of multifocal motor neuropathy

Objective: To analyze the clinical and electrophysiological features of the multifocal motor neuropathy (MMN). Methods: All 7 patients with MMN were followed up for 0.7 to 3.4 years. The onset and development features were clinically summarized. Conventional motor and sensory nerve conduction, F wave, EMG, single fiber EMG (SFEMG), segment motor nerve conduction and Inching technique were performed. The relations between clinic and eletrophysiology were analyzed. Results: The first symptom in all patients was weakness in single limb without remarkable sensory symptoms. With the very slow progression of the disease, more and more areas were involved. Motor findings including the asymmetric and distal were greater than the proximal weakness and showed various degrees of muscular atrophy. High titers serum IgG and IgM anti-GM 1 antibodies were found in only one patient. 16 segments with conduction block (CB) and 6 segments with probable CB were detected. CB were presented in 5 segments of the 2 nerves in which clinic features and EMG were normal, the other 17 segments with CB or probable CB were detected in 12 nerves which showed mild to moderate weakness clinically. Follow-up of segment motor nerve conduction in 1 patient showed that a new CB was detected in left ulnar nerve, while a CB identified in right median nerve 16 months ago disappeared due to a significant decrease in the distal CMAP amplitude. SFEMG showed an increased jitter and fiber density in 4 patients. Standard EMG showed neurogenic disorders in all muscles with weakness and atrophy, abnormal EMG was also found in some clinically normal muscles in 3 patients, but the percentage of the increased duration and amplitude of motor unit potential was discrepancy in different muscles innervated by different nerves in the same patient. F wave was absent in 3 nerves of 3 patients and frequency of F wave decreased in 1 nerve of 1 patient. Decreased distal amplitude of CMAP was found in all muscles with atrophy. Conclusion: Clinical features are one of the most important factors in diagnosis of MMN, but it is hard to diagnose definite MMN without CB, although CB doesn't completely consist with clinical manifestations.