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.

1. Van den Bergh, P. Y., van Doorn, P. A., Hadden, R. D., Avau, B., Vankrunkelsven, P., Allen, J. A., et al. (2021). European Academy of Neurology/Peripheral Nerve Society guideline on diagnosis and treatment of chronic inflammatory demyelinating polyradiculoneuropathy: Report of a joint task force—second revision. Journal of the Peripheral Nervous System, 26(3), 242–268. https://doi.org/10.1111/jns.12455
2. Merkies, I. S., van Nes, S. I., Hanna, K., Hughes, R. A., & Deng, C. (2010). Confirming the efficacy of intravenous immunoglobulin in CIDP through minimum clinically important differences: Shifting from statistical significance to clinical relevance. Journal of Neurology, Neurosurgery & Psychiatry, 81(11), 1194–1199. https://doi.org/10.1136/jnnp.2010.205732
3. van Nes, S. I., Vanhoutte, E. K., van Doorn, P. A., Hermans, M., Bakkers, M., Kuitwaard, K., et al. (2011). Rasch-built overall disability scale (R-ODS) for immune-mediated peripheral neuropathies. Neurology, 76(4), 337–345. https://doi.org/10.1212/WNL.0b013e318208824b
4. Koski, C. L., Baumgarten, M., Magder, L. S., Barohn, R. J., Goldstein, J., Graves, M., et al. (2009). Derivation and validation of diagnostic criteria for chronic inflammatory demyelinating polyneuropathy. Journal of the Neurological Sciences, 277(1-2), 1–8. https://doi.org/10.1016/j.jns.2008.09.035
5. Benoit, C., Svahn, J., Debs, R., Vandendries, C., Lenglet, T., Zyss, J., et al. (2021). Focal chronic inflammatory demyelinating polyradiculoneuropathy: Onset, course, and distinct features. Journal of the Peripheral Nervous System, 26(2), 193–201. https://doi.org/10.1111/jns.12444
6. Rajabally, Y. A., Nicolas, G., Piéret, F., Bouche, P., & Van den Bergh, P. Y. (2009). Validity of diagnostic criteria for chronic inflammatory demyelinating polyneuropathy: A multicentre European study. Journal of Neurology, Neurosurgery & Psychiatry, 80(12), 1364–1368. https://doi.org/10.1136/jnnp.2009.179358
7. Rajabally, Y. A., Afzal, S., Loo, L. K., & Goedee, H. S. (2022). Application of the 2021 EAN/PNS criteria for chronic inflammatory demyelinating polyneuropathy. Journal of Neurology, Neurosurgery & Psychiatry, 93(12), 1247–1252. https://doi.org/10.1136/jnnp-2022-329815