Abstract Details

Chronic inflammatory demyelinating polyneuropathy (CIDP) is characterized on nerve conduction study (NCS) by prolonged distal latencies, slowed conduction velocities, prolonged late responses, conduction blocks, and temporal dispersion. Unmyelinated fibers typically conduct action potentials at speeds of 0.5-10 m/s; myelinated fibers conduct an order of magnitude faster, e.g. 50-70 m/s. While very slow conduction velocities < 25 m/s are typically associated with the genetic neuropathies as in the Charcot-Marie Tooth neuropathies, CIDP can manifest with slow conduction velocities. Prompt recognition of CIDP is crucial for the timely initiation of immunotherapy.

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This case series of three CIDP patients demonstrates very slow conduction velocities and prolonged distal latencies. An 81-year-old woman with history of multiple sclerosis and chronic myelogenous leukemia presented with inability to walk over a few months with diffuse sensory loss. NCS showed absent motor responses in the leg, partial conduction blocks in the arm, prolonged ulnar motor distal latency 7.9 ms (normal ≤3.4ms), and very slow conduction velocities < 15 m/s.

A 50-year-old woman with prior history of COVID-19 presented with diffuse weakness. NCS showed ulnar motor distal latency of 23.2 ms, slowed motor conduction velocities < 30 m/s. After treatment initiation with intravenous immunoglobulin, sensory responses improved, and conduction velocities increased to > 30 m/s.

A 49-year-old woman presented with 3 months of bilateral weakness and sensory symptoms two weeks after a COVID-19 vaccination. NCS showed ulnar motor distal latency of 14 ms and slowed motor conduction velocities < 30 m/s.

Very slow conduction velocities are a feature not just of the genetic neuropathies but also of acquired demyelination as seen in CIDP, and the latter is distinguished by abnormal temporal dispersion and conduction blocks. Astute electrophysiologists should modify sweep speed and gain to increase sensitivity for delayed or dispersed responses.