[Three Cases of Small-Cell Lung Cancer with Anti-Hu Antibody-Positive Paraneoplastic Neurological Syndrome].

This case series discusses 3 male patients in their 60s who presented with a chief complaint of sensory disorder in the upper or lower limbs. The patients were diagnosed with small-cell lung cancer(SCLC)with anti-Hu antibody-positive paraneoplastic neurological syndrome(PNS). Chest radiography at the initial visit revealed abnormalities in only one of the 3 cases. To confirm the diagnosis, a bronchoscopy was performed. However, the diagnosis could be confirmed in only 1 patient. In the other 2 patients, a diagnosis could not be made due to the small size of the primary lung tumor. The diagnosis was confirmed in the other 2 cases using endobronchial ultrasound-guided transbronchial needle aspiration at another hospital. Chemoradiotherapy led to tumor reduction in 2 patients. However, in all patients, the neurological symptoms could not be resolved with steroids, immunoglobulin, or anti-tumor treatment. For neurological disorders due to possible PNS, the anti-Hu antibody test, chest computed tomography, and ultrasonic bronchoscopy should be performed to ensure early diagnosis and treatment of SCLC.

Paraneoplastic Opsoclonus-myoclonus Syndrome with Anti-Hu and Anti-SOX-1 Antibodies after Immune-checkpoint Inhibitor Treatment Combined with Chemotherapy in a Patient with Small-cell Lung Cancer.

A 69-year-old man with advanced small-cell lung cancer achieved partial remission after 3 courses of immunochemotherapy that included atezolizumab. Ten days after the last treatment, he developed paraneoplastic opsoclonus-myoclonus syndrome and required mechanical ventilation. Serology testing detected anti-Hu and anti-SOX-1 antibodies. Despite steroid pulse therapy, various anticonvulsants, continuous intravenous sedation, and a fourth course of chemotherapy without atezolizumab, his condition failed to improve. Paraneoplastic opsoclonus-myoclonus syndrome with autoantibodies after immune-checkpoint inhibitor treatment has not been reported previously. Although a causal relationship between immune-checkpoint inhibitors and paraneoplastic syndromes has been suggested, the mechanism remains unknown.