Classic stiff person syndrome (SPS) is characterized by excessive contraction of lower extremity muscles and paraspinal muscles, trunk muscles, cervical paracarbospinal muscles, and abdominal muscles with pain. Due to its rarity, and the lack of early typical manifestations and imaging signs, the misdiagnosis rate is high.

Anti-GAD65 antibodies were positive. Electromyography revealed findings consistent with the electrophysiological changes of SPS (continuous motor unit activity in the extensor digitorum brevis, anterior tibialis and gastrocnemius muscles at rest). Chest computed tomography (CT) of the abdomen and pelvis revealed a space occupying lesion in the left adrenal area. The patient received gamma-aminobutyric acid therapy combined with glucocorticoid, standard human immunoglobulin and monoclonal antibody to control the disease with good results. After excluding surgical contraindications, a laparoscopic left adrenalectomy was planned. But the patient refused the operation as the muscles of the waist and limbs were found to be stiff and the tumor could not be removed under anesthesia. 

SPS is very rare in clinic, which deserves attention in clinical practice. Early diagnosis and treatment can help patients to prevent it better.

Therefore, summarizing the characteristics of SPS, raising awareness of the disease, reducing missed diagnosis and promoting early diagnosis are essential. Further studies are expected to reveal the heterogeneous characteristics of SPS.