Is distal motor and/or sensory demyelination a distinctive feature of anti-MAG neuropathy?

To report the frequency of the different patterns of sensory and motor electrophysiological demyelination distribution in patients with anti-MAG neuropathy in comparison with patients with IgM neuropathy without MAG reactivity (IgM-NP). Thirty-five anti-MAG patients at early disease stage (20.1 months) were compared to 23 patients with IgM-NP; 21 CIDP patients and 13 patients with CMT1a neuropathy were used as gold standard neuropathies with multifocal and homogeneous demyelination, respectively. In all groups, standard motor and sensory electrophysiological parameters, terminal latency index and modified F ratio were investigated. Motor electrophysiological demyelination was divided in four profiles: distal, homogeneous, proximal, and proximo-distal. Distal sensory and sensorimotor demyelination were evaluated. Anti-MAG neuropathy is a demyelinating neuropathy in 91 % of cases. In the upper limbs, reduced TLI is more frequent in anti-MAG neuropathy, compared to IgM-NP. But, predominant distal demyelination of the median nerve is encountered in only 43 % of anti-MAG neuropathy and is also common in IgM-NP (35 %). Homogeneous demyelination was the second most frequent pattern (31 %). Concordance of electrophysiological profiles across motor nerves trunks is low and median nerve is the main site of distal motor conduction slowing. Reduced sensory conduction velocities occurs in 14 % of patients without evidence of predominant distal slowing. Simultaneous sensory and motor distal slowing was more common in the median nerve of anti-MAG neuropathy than IgM-NP. Electrophysiological distal motor demyelination and sensory demyelination are not a distinctive feature of anti-MAG reactivity. In anti-MAG neuropathy it is mainly found in the median nerve suggesting a frequent nerve compression at wrist.