Anti-Hu Paraneoplastic Polyradiculoneuropathy Masquerading As Guillain-Barré Syndrome: A Case Report.

Paraneoplastic neurological syndromes (PNS) can precede the detection of an underlying malignancy and often mimic more common neurological conditions, leading to significant diagnostic delays. This report describes a case of anti-Hu (ANNA-1)-associated PNS that closely mimicked Guillain-Barré syndrome (GBS). A 47-year-old male presented with acute ascending flaccid weakness following a respiratory infection. Cerebrospinal fluid analysis demonstrated albuminocytologic dissociation, supporting an initial diagnosis of GBS. The patient showed a poor clinical response to intravenous immunoglobulins. Further investigation identified a right upper lobe lung mass, which biopsy confirmed as small-cell lung carcinoma. The presence of high-titer anti-Hu antibodies (1:7680) established a definitive diagnosis of paraneoplastic polyradiculoneuropathy. Despite aggressive treatment with chemotherapy, immunotherapy, and plasma exchange, his neurological status deteriorated, culminating in hypercapnic respiratory failure necessitating tracheostomy. His hospital course was further complicated by iatrogenic osmotic demyelination syndrome secondary to rapid sodium correction. The patient ultimately died from his condition. This case underscores that a treatment-resistant, GBS-like presentation may be the initial manifestation of a severe paraneoplastic syndrome. A lack of response to standard immunomodulatory therapy should prompt an expedited search for an occult malignancy and associated onconeural antibodies, as the PNS itself often dictates a grave prognosis. Additionally, this case highlights the heightened vulnerability of such patients to serious iatrogenic complications from routine medical management.