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

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. 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. 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. Terminal latency index and distal motor latency of median nerve, distal motor latency and 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. 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. 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.