Nerve pathology distinguishes focal motor chronic inflammatory demyelinating polyradiculoneuropathy from multifocal motor neuropathy

Objectives: The objective of the study is to distinguish the mechanisms of disease for chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and multifocal motor neuropathy (MMN), which we believe to be fundamentally different. However, distinguishing the mechanisms is more difficult when the presentation of CIDP is motor-predominant, focal, or asymmetric.

Methods: We describe 3 focal, motor-predominant, representative cases that could be interpreted on clinical and/or electrophysiological grounds as either MMN or focal CIDP, and present pathological findings.

Results: We highlight pathological differences in these cases, and provide an argument that CIDP and MMN are distinct entities with different pathophysiological mechanisms-chronic demyelination for CIDP, and an immune-mediated attack on paranodal motor axons for MMN.

Conclusions: Based on clinical evaluation, electrophysiology, and nerve biopsy pathology, we can divide the conditions into inflammatory demyelinating neuropathy (focal CIDP) versus chronic axonal neuropathy (MMN). The divergent pathological findings provide further evidence that CIDP and MMN are fundamentally different disorders.