[A case of anti-Kelch-like protein 11 (KLHL11) antibody-positive opsoclonus-myoclonus syndrome associated with small cell lung cancer that improved after immunotherapy and cancer treatment].

Opsoclonus-myoclonus syndrome (OMS), characterized by symptoms including rapid eye movements, myoclonus, and cerebellar ataxia, is one of the paraneoplastic neurological syndrome. A 68-year-old woman was admitted with oscillopsia, dizziness, and gait disturbance caused by postural tremor. Clinical evaluation led to a diagnosis of Kelch-like protein 11 (KLHL11)-associated paraneoplastic OMS, secondary to small cell lung cancer (cT1cN3M1a, stage 4A). In most cases, the improvement of the neurological symptoms is limited unless the underlying malignancy is effectively treated. Therefore, cancer therapy in combination with immunotherapy is essential, even in patients with poor performance status. Here, we report a case in which both immunotherapy and cancer treatment led to improvement in neurological symptoms associated with KLHL11-related paraneoplastic OMS.