僵體症候群 (stiff person syndrome, SPS) 為一種罕見的自體免疫性神經疾病，其特徵為軀幹及近端肢體肌肉出現漸進性肌肉僵硬和陣發性肌肉痙攣，易受情緒激動、聲音與體覺刺激而誘發。SPS 不容易診斷，因有嚴重肌肉僵硬現象，臨床上易誤診為其他疾病。目前尚未有能治癒之藥物，常用藥物治療在於緩解患者症狀及調節潛在的異常免疫反應，例如：肌肉鬆弛劑、苯二氮平類 (benzodiazepines)、靜脈注射免疫球蛋白 (intravenous immunoglobulin)、血漿置換術 (plasmapheresis)、抗cluster of differentiation 20 (CD20) 單株抗體 (rituximab)。對於benzodiazepines 和其他肌肉鬆弛劑治療無效之患者，rituximab 可作為臨床替代治療選項之一。然而，過去相關文獻報導並不多，療效不明確。藉由本案例之討論，以累積臨床上使用的經驗。

Stiff person syndrome (SPS) is a rare autoimmune neurological disease, the symptom is progressive muscle stiffness (rigidity) and paroxysmal muscle spasms in the trunk and proximal limb, and it was often induced by emotional excitement, sound, and body stimulation. Due to its severe muscle stiffness, SPS is difficult to diagnose, and liable to be misdiagnosed as other disease in clinical practice. Up to present, SPS has no curable medication, standard clinic treatment is aimed to relieve the symptoms and/or modulate the underlying abnormal immune process; such as muscle relaxants, benzodiazepines, intravenous immunoglobulin, plasmapheresis, and rituximab. For patients who failed in treatment of benzodiazepines and other muscle relaxants, rituximab can be used as one of the clinical alternative treatment options. However, the therapeutic effect of rituximab was not many reported in the past and the efficacy was not clear as well. Therefore, we expected this case study could accumulate some experience in clinical practice.