Clinical-neurophysiological correlations in a series of patients with IgM-related neuropathy

Objective: We aim to draw clinical-neurophysiological correlations in our cohort of patients affected by IgM-related neuropathy to investigate whether neurophysiological parameters may help differentiate the classical phenotype from atypical forms. Methods: We retrospectively evaluated patients with IgM-related neuropathy referred to our Institute from 1990 to 2011. All patients underwent extensive laboratory, clinical and neurophysiological evaluation. Results: A classic sensory-ataxic form was observed in 20 of 34 patients, while an atypical phenotype (multiple mononeuropathy, polyneuropathy with predominant motor impairment, painful small-fibre neuropathy) was identified in the remaining 14 cases. Nerve conduction studies revealed in almost all cases a pattern typical of demyelination. A reduced terminal latency index and a prolonged distal motor latency of median nerve, as well as a prolonged distal motor latency and a reduced motor conduction velocity of peroneal nerve when recorded from extensor digitorum brevis, were significantly associated with classic sensory-ataxic phenotype. Conversely, a compound muscle action potential amplitude reduction of peroneal nerve from the tibialis anterior, was mostly associated with atypical forms. Conclusions: No clear electrophysiological differences between classical forms and atypical cases can be identified in IgM-related neuropathy. Still, we demonstrated that demyelinating abnormalities are more often associated with classical phenotypes, while axonal impairment occurs more often in atypical clinical patterns. Significance: Performing correlations between clinical and neurophysiological findings in IgM-related neuropathy may help to better understand different disease mechanisms in this heterogeneous form of inflammatory neuropathy.