Central sleep apnea as an initial presentation of small cell lung carcinoma with anti-Hu antibody-related paraneoplastic neurologic syndrome.

Anti-Hu antibody-related paraneoplastic neurologic syndrome (PNS), a rare disease primarily associated with small cell lung carcinoma, is characterized by diverse neurologic manifestations. Central sleep apnea, although rare, is specific to anti-Hu antibody-related PNS. Herein, we present a case of out-of-hospital cardiac arrest attributed to hypercapnic central sleep apnea and detail the subsequent workup that revealed anti-Hu brainstem encephalitis. A malignancy survey revealed mediastinal small cell carcinoma. The patient was treated by tumour excision, chemotherapy, plasma exchange, and high-dose glucocorticoids. Though the neurologic damage caused by anti-Hu antibody was documented to be relatively irreversible in literatures, such hypercapnic central sleep apnea resolved in our case about 1 month later.