THU356 Muscle Pain In A Diabetic: Think Outside The Box

Disclosure: R. Ellangovan: None. M. Rizk: None. V. Singh MD: None. C. Sherpa: None. Introduction: Stiff person syndrome (SPS) is a rare immunological disorder associated with GAD antibody-spectrum disorders and characterized by rigidity and painful muscle spasms. SPS has a prevalence of 1-2 cases per million and affects females more than men. We present a case of SPS who was admitted for progressive muscle pain and rigidity causing impaired ambulation. Case Presentation: A 60-year-old female with a two-year history of type 2 diabetes, Graves' disease was diagnosed with acral lentiginous melanoma of the left foot. One month after Nivolumab immunotherapy, she converted to type 1 diabetes with low C-peptide and positive GAD antibody. She was admitted with severe muscle pain and spasms in her lower extremities and trunk, debilitating enough to make her bedbound. Her muscle strength and sensory function were intact. MRI of thigh was concerning for myositis versus diabetic myonecrosis. She was initiated on NSAIDs with no improvement. Core muscle biopsy revealed necrosis and granulation tissue with no evidence of malignancy. Extensive work up including myositis panel and myasthenia gravis panel were negative. The presence of GAD antibodies and no improvement to NSAIDs, prompted suspicion for SPS. The patient declined lumbar puncture (LP) for further evaluation. Diazepam showed mild improvement. Due to persistent severe symptoms, she was treated with IVIG for 5 days that resulted in marked improvement. Discussion: There is no gold standard test for definitive diagnosis of SPS. Classic features of SPS include muscle spasms, pain, and rigidity typically involving the trunk and lower extremities. There are GAD antibodies in serum and CSF and glycine receptor or amphiphysin antibodies. EMG study will show continuous motor unit activity in affected muscles. A robust response to muscle relaxants like GABA agonists and exclusion of alternative neurological disorder favors SPS. LP or EMG was not performed on this patient, yet she met other criteria including the presence of other GAD disorders like type 1 diabetes. Current recommended therapy for symptomatic relief includes GABA agonists or baclofen. If no improvement is noted, IVIG can be considered. Plasmapheresis and rituximab have been used with variable efficacy. Prognosis is variable and many patients experience disability despite combining multiple therapies. Hence it is crucial to have a high index of suspicion in GAD spectrum disorders for early recognition and prompt treatment. Presentation: Thursday, June 15, 2023