Thymoma-associated stiff-person syndrome successfully treated with extended thymectomy: a case report

BACKGROUND: Stiff-person syndrome (SPS) is a rare autoimmune neurological disorder characterized by painful muscle stiffness and spasms. Paraneoplastic SPS associated with thymoma is rare. Here, we describe a rare case in which neurological symptoms improved after extended thymectomy. CASE PRESENTATION: A 60-year-old woman presented with progressive painful muscle spasms and gait disturbances affecting the lower extremities. Neurological imaging revealed no structural abnormalities; however, both serum and cerebrospinal fluid were positive for anti-glutamic acid decarboxylase (GAD) antibodies, leading to a diagnosis of SPS. Despite receiving immunotherapy and symptomatic treatment, the patient's neurological symptoms persisted. Contrast-enhanced chest computed tomography revealed a small anterior mediastinal tumor suspected to be a thymoma. Subsequently, bilateral thoracoscopic extended thymectomy was performed. Histopathological examination confirmed a WHO type B1 thymoma (Masaoka stage I), and her neurological symptoms gradually improved postoperatively. Two years after surgery, she was able to walk independently and climb stairs without assistance. CONCLUSION: This case suggests that extended thymectomy may contribute to sustained neurological and functional improvement in selected patients with thymoma-associated SPS, even in the absence of normalization of the anti-GAD antibody titer.