S4277 Gut Dysmotility in Anti-Hu Paraneoplastic Syndrome With Small Bowel Adenocarcinoma and Nasopharyngeal Squamous Cell Carcinoma

Introduction: Anti-Hu syndrome is a rare paraneoplastic syndrome most associated with small cell lung cancer. Paraneoplastic syndromes associated with anti-Hu antibodies are diverse, including gastrointestinal (GI) symptoms of dysmotility and dysphagia. We present a novel case of Anti-Hu syndrome following resected metastatic small bowel adenocarcinoma with progressive neurologic decline, severe dysphagia, and concurrent nasopharyngeal squamous cell carcinoma (SCC). Case Description/Methods: A 66-year-old man with metastatic small bowel adenocarcinoma presented with 2 months of cognitive decline, hallucinations, dysphagia, and lower extremity weakness. Encephalopathy workup was unrevealing. Magnetic resonance imaging brain revealed white matter hyperintensities consistent with mild chronic microvascular disease and nasal masses diagnosed on biopsy as poorly differentiated nasopharyngeal SCC. Lumbar spine magnetic resonance imaging showed enhancement of the cauda equina and conus medullaris suggesting an inflammatory process. Endoscopy revealed candida esophagitis without obstruction; however, dysphagia persisted despite eradication. Modified barium swallow study showed pharyngeal and esophageal dysmotility with minimal to no esophageal clearance and contrast retention. Paraneoplastic anti-Hu (ANNA-1) antibodies were positive in both cerebrospinal fluid and serum. He was treated with high-dose corticosteroids and intravenous immunoglobulin. Hallucinations resolved and mentation and lower extremity strength improved but dysphagia persisted requiring gastric tube placement. Discussion: This case highlights anti-Hu paraneoplastic syndrome manifesting as immune-mediated encephalitis, motor neuronopathy, and dysphagia. While traditionally associated with small cell lung cancer, this patient’s small bowel adenocarcinoma and nasopharyngeal SCC raise questions about broader tumor associations. Anti-Hu is associated with cranial and sensory neuropathies, cerebellar ataxia, and limbic encephalitis. Cranial neuropathies involving the vagus nerve affect the enteric nervous system. GI symptoms are initial features in 12% of cases and develop in nearly 23% of patients. Gastroparesis is most common, but anti-Hu can affect any GI segment, causing pseudo-obstruction, ileus, or dysphagia. This is the first report of anti-Hu in a patient with small bowel adenocarcinoma and nasopharyngeal SCC. GI symptoms may precede diagnosis, thus, Gastroenterologists should maintain high suspicion for paraneoplastic syndromes in patients with unexplained dysmotility.