Focal Chronic Inflammatory Demyelinating Polyneuropathy - A Case Report with Clinical Application and Validation of 2021 European Academy of Neurology/Peripheral Nerve Society Criteria.

The updated 2021 criteria of the European Academy of Neurology/Peripheral Nerve Society (EAN/PNS) for chronic inflammatory demyelinating polyneuropathy (CIDP) has excellent diagnostic sensitivity and specificity for typical and variants of CIDP. For focal CIDP, applications of these criteria may be different due to limited peripheral nerve involvement. We illustrate using a rare case of focal CIDP on the applicability of 2021 EAN/PNS criteria and its practical limitations. A young woman presented with progressive right foot drop and numbness over 5 years. Clinically, she had areflexic right lower limb monoparesis with a sensory deficit over the dorsum of the right foot. A nerve conduction study showed normal right peroneal distal compound motor action potential but marked temporal dispersion with conduction block and significantly prolonged F-waves latency suggestive of demyelination. Right sural sensory nerve action potentials (SNAPs) were small in amplitude with the absence of right superficial peroneal SNAP. These findings suggested a focal sensorimotor acquired demyelinating neuropathy involving right lower limb nerves and fulfilled possible focal CIDP as per the 2021 EAN/PNS criteria. Cerebrospinal fluid (CSF) analysis revealed albuminocytological dissociation. Magnetic resonance imaging of the lumbosacral plexus was unremarkable. She received intravenous methylprednisolone, followed by oral prednisolone and mycophenolate mofetil. Clinically, right lower limb power is in parallel with functional scores. With an objective positive clinical response to treatment in addition to elevated CSF protein as supportive criteria, the diagnosis of possible focal CIDP was upgraded to focal CIDP. The inclusion of supportive criteria in the updated EAN/PNS diagnostic criteria improves diagnostic certainty in focal CIDP.