Introduction: Multifocal motor neuropathy with conduction block is an immune-mediated motor neuropathy, which usually responds to intravenous immunoglobulin. However, efficacy of long-term intravenous immunoglobulin is controversial. Our aim was to establish the long-term effects of intravenous immunoglobulin therapy on clinical and neurophysiological outcome measures and to determine the criteria predicting a good response to long-term intravenous immunoglobulin treatment.
Methods: We retrospectively included all multifocal motor neuropathy with conduction blocks patients followed for at least 4 years who received intravenous immunoglobulin therapy. We compared clinical data, MRC sumscores and electrophysiological data between the first and the last examination in the department.
Results: Seventeen patients were followed for an average of 8 years (range 4 to 18 years). At last examination, weakness remained asymmetric, predominant in the upper limbs, with a peripheral nerve distribution. At last examination, 3 patterns of evolution was seen: 6/17 patients had muscle strength improvement and need no more intravenous immunoglobulin therapy, 6/17 had initial improvement but became intravenous immunoglobulin dependent and 5/17 did not respond to intravenous immunoglobulin. MRC sumscores, number of conduction blocks and distal compound muscle action potential amplitudes were comparable between the first and the last examination (p>0.05). Improvement of MRC sumscores was not correlated with the clinical, biological and electrophysiological data that we analysed: age, gender, duration of disease, time from onset to intravenous immunoglobulin therapy, number of involved nerves, number of affected limbs, presence of muscle atrophy, MRC sumscores at diagnosis, number of conduction blocks, mean amplitude of the motor evoked potentials, presence of anti-GM1 antibodies, titers and IgM or IgG type of anti-GM1 antibodies.
Conclusions: In this study, one third of multifocal motor neuropathy with conduction blocks patients have clinical improvement at last examination and need no more treatment, one third are intravenous immunoglobulin dependent and one third have never responded to intravenous immunoglobulin. Electrophysiological data are comparable between the first and the last examination. No predictive factor has been disclosed for long-term response to intravenous immunoglobulin.