Are electrophysiological features related to disability in patients with anti-MAG neuropathy?

OBJECTIVES: To explore clinical-neurophysiological correlations in anti-myelin-associated glycoprotein (anti-MAG) neuropathy. METHODS: Clinical and electrophysiological data of 42 patients with anti-MAG neuropathy were retrospectively analysed. Disability was evaluated using the Overall Neuropathy Limitation Scale (ONLS), motor impairment through MRC sum score and sensory deficiency through INCAT sensory score. Compound motor action potential (CMAP) sum score was calculated adding the distal CMAP amplitude of the median, ulnar, tibial and fibular nerves of both sides. RESULTS: In multivariate analysis, motor impairment was associated with CMAP sum score (r=0.35, P=0.047) and distal motor latency in the median nerves (r=-0.45 P=0.012), sensory deficiency was related to motor conduction velocity in the median nerve (r=-0.65. P=0.02). Disability was correlated with CMAP sum score (r=-0.37, P=0.022). CONCLUSION: Electrophysiological features are associated with clinical involvement in anti-MAG neuropathy. Reduction of CMAP amplitudes reflects distal motor latency delay and is mainly due to axonal loss. Since it is related to muscle weakness and disability, CMAP sum score may be a good marker in the evaluation of patients with anti-MAG neuropathy.

Do patients having a decrease in SNAP amplitude during the course of MMN present with a different condition?

A decrease in sensory nerve action potentials (SNAP) amplitude has been recently reported in some patients during the course of multifocal motor neuropathy with conduction blocks (MMNCB). It is not known if those patients have different clinical expression and disability when compared with typical MMNCB. Clinical, biological and electrophysiological assessments were performed in 15 patients fitting the diagnosis criteria of MMNCB, including normal SNAP amplitude at initial examination. Patients presenting with nerve entrapment or associated disease causative of sensory neuropathy were excluded. Median time of follow-up was 3 years (1-17 years). At the last examination, four patients had at least one SNAP amplitude below 50% of normal value. None had clinically objective sensory loss. Clinical and electrophysiological data obtained at the last examination were compared between patients with normal SNAP amplitude and patients with decreased SNAP amplitude. No difference between both population in term of age, sex, disease duration, anti-GM1 antibody titers, CSF data and number of conduction blocks was noted. In contrast, patients with decreased SNAP amplitude had worse overall neuropathy limitation scale (ONLS) scores (7 vs. 2; p = 0.02), a higher number of affected nerves (12.5 vs. 4; p = 0.018), a higher number of affected limb regions (6 vs. 2; p = 0.019) and lower median CMAP amplitude (2 mV vs. 6.5 mV; p = 0.04). They were all dependent on higher doses of IVIg (1.4 g/(kg 4 weeks vs. 0.6; p = 0.018). A reduction in SNAP amplitude during the course of MMNCB is associated with a more severe disease and a more prominent axonal loss. This result needs to be confirmed in a larger cohort.