Focal CIDP is a rare CIDP variant manifesting clinically with sensorimotor symptoms in one limb.

We retrospectively reviewed patients with focal onset and nerve biopsy confirmation of inflammatory demyelination. Patients with ongoing single limb involvement were classified as “chronic inflammatory demyelinating mononeuropathy” (CIDM), while those with additional limb involvement were classified as multifocal CIDP.

Fifty-four patients had monomelic onset (pure sensory n=5; pure motor n=14; sensorimotor n=35) with pathological inflammatory demyelination (segmental demyelination on teased fibers n=44; thinly myelinated axons n=53; small onion bulbs n=43; inflammation n=69). In forty patients, symptoms remained monomelic over median follow-up of 52 months (range 14-397)(CIDM group), while 14 patients developed multiple limb involvement with median follow-up of 149.5 months (range 12-435)(multifocal CIDP group). Sciatic nerve (n=26/54) then brachial plexus (n=15/54) were most commonly affected. Pain was uncommon (n=10[18%]). Most CIDM patients did not fulfill EAN/PNS electrophysiological criteria for demyelination (definite n=5/40[12.5%]; possible n=10/40[25%]). CSF protein was mostly abnormal (n=29/33), but mildly (median 50 mg/dL). All had focal MRI nerve abnormalities of the affected limb (diffuse T2 hyperintensity/thickened nerve roots) guiding biopsy-site (dorsal rootlet n=3; targeted fascicular n=53; distal cutaneous nerve n=13). Thirty-two CIDM patients started immunotherapy (IVIg n=25[78%]; intravenous methylprednisolone n=3[9%]; plasmapheresis n=4[13%]). CIDM patients showed significant improvement in median NIS at last follow-up(18 to 11.7, p=0.042).

CIDM presents as a focal inflammatory demyelinating neuropathy that is difficult to diagnose as most cases (63%) do not meet CIDP electrophysiological criteria and only have mild elevation of CSF protein.  Our study shows that focal CIDP usually remains localized (74%) over many years, is responsive to immunotherapy, and is hard to diagnose, making the use of MRI and targeted nerve biopsy important tools in its evaluation.