Anti-Hu with Paraneoplastic Encephalomyelitis and Small-Cell Lung Cancer: A Case and Review

Paraneoplastic neurological syndromes (PNS) are rare disorders caused by an immune response against neuronal antigens expressed by an underlying malignancy. Anti-Hu-associated paraneoplastic encephalomyelitis (PEM) is one of the most recognized forms, often linked to small-cell lung cancer (SCLC). We report a case of a patient presenting with rapidly progressive cognitive decline, seizures, and peripheral neuropathy. Extensive investigations revealed positive anti-Hu antibodies, suggesting a paraneoplastic etiology. Imaging studies showed limbic system involvement, and a thorough oncological workup confirmed an underlying SCLC. Despite tumor-directed therapy and immunomodulatory treatment, the patient exhibited only partial neurological improvement. This case highlights the challenges in diagnosing anti-Hu-associated PNS due to its heterogeneous presentation and the frequent delay in identifying the underlying malignancy. Early detection and prompt treatment are crucial, as neurological symptoms often precede tumor diagnosis. We discuss the pathophysiology, diagnostic approach, and current treatment strategies, emphasizing the importance of a multidisciplinary approach in managing PNS. This case underscores the necessity for heightened clinical suspicion and early antibody testing in patients with unexplained neurological syndromes, particularly in those at risk for malignancy.