A case of severe paraneoplastic glutamic acid decarboxylase antibody‐spectrum disorder with improvement through prior immunotherapy before surgical intervention

Abstract Background Initially associated with stiff‐person syndrome, antibodies to glutamic acid decarboxylase (GAD) antibodies are now recognized as indicators of GAD antibody‐spectrum disorders (GAD‐SD), which encompass cerebellar ataxia, autoimmune epilepsy and limbic encephalitis. Paraneoplastic neurological syndromes associated with GAD‐SD are rare, and optimal timing of surgical intervention and impact on neurological symptoms remain poorly understood. Case Presentation We present the case of a 65‐year‐old woman who developed overlapping symptoms of cerebellar ataxia and stiff‐person syndrome detected through high‐titer GAD antibodies in both serum and cerebrospinal fluid, alongside the presence of a thymoma. Due to severe dysphagia and gait ataxia that rendered her bedridden on admission, surgical intervention was initially deferred. Instead, she received immunotherapies including intravenous methylprednisolone and intravenous immunoglobulin, which remarkably improved neurological symptoms. However, a decline in symptoms occurred on tapering oral prednisolone. Subsequently, a thoracoscopic thymectomy was carried out 27 months after symptom onset, leading to further neurological improvement and successful reduction of prednisolone. Conclusion In paraneoplastic GAD‐SD cases with severe symptoms at presentation, prioritizing immunotherapy and considering surgical intervention once the symptoms have stabilized might be advantageous.