To report  severe demyelinating GBS variant with anti-GM1 IgG antibodies following purified chick embryo cell (PCEC) antirabies vaccination, highlighting the need for vigilance in post-vaccination neurological decline.

Vaccine-associated GBS is rare but recognized, historically linked to older neural-tissue rabies vaccines. Newer PCEC vaccines are considered safer; however, recent large-scale data suggest a statistically significant association with GBS, warranting re-evaluation of post-vaccination surveillance thresholds.

Single-patient observational report with clinical, biochemical, cerebrospinal fluid, electrodiagnostic, antibody, and radiologic correlation with follow-up at 3 months

A 25-year-old woman developed descending sensorimotor weakness, facial diplegia, bulbar dysfunction, and autonomic involvement — including urinary retention — three days after the third dose of PCEC antirabies vaccine administered following a monkey bite. No antecedent respiratory or gastrointestinal infection was identified.

CSF demonstrated albuminocytologic dissociation (protein 283 mg/dL, normal cell count). Neurotropic virus panel was negative. Anti-GM1 IgG antibodies were detected — an antibody classically associated with axonal variants but identified here in a demyelinating phenotype. Nerve conduction studies showed prominent conduction block, prolonged distal latencies, slowed conduction velocities, and temporal dispersion in median and peroneal nerves, consistent with severe acquired demyelinating polyneuropathy. Respiratory compromise necessitated mechanical ventilation.

Following seven sessions of plasmapheresis (40 mL/kg/session), the patient was extubated at day 7. Limb power improved to MRC 4/5. Repeat NCS at 4 weeks showed resolution of conduction block with partial normalization of distal latencies. At 3-month follow-up, full limb power was restored with only mild residual facial weakness.

This case demonstrates that PCEC antirabies vaccination can be associated with severe demyelinating GBS with atypical anti-GM1 IgG seropositivity. The descending pattern of weakness risks misdiagnosis — with botulism, diphtheria, and acute intermittent porphyria in the differential. A low threshold for early electrodiagnostic evaluation and plasmapheresis initiation is critical. As rabies vaccination expands globally, post-vaccination neurological surveillance protocols require strengthening.