SUN-557 Unmasking the Autoimmune Triad: Diabetic Ketoacidosis Revealing Stiff Person Syndrome and Systemic Sclerosis

Abstract Disclosure: D. Deyar: None. D. Rosenberg: None. Introduction: Autoimmune diseases often present with overlapping features, delaying diagnosis and proper management. Diabetes mellitus, traditionally classified as type 1 or type 2, includes latent autoimmune diabetes in adults (LADA), an underdiagnosed condition that may initially mimic type 2 diabetes. Stiff person syndrome (SPS), a rare autoimmune neurological disorder, and systemic sclerosis, a connective tissue disease, are rarely linked to diabetes but may share a common autoimmune pathogenesis. This case highlights the diagnostic complexity of a patient presenting with diabetic ketoacidosis (DKA), revealing underlying SPS and systemic sclerosis. Clinical Case: A 47-year-old male with a history of asthma and GERD initially presented outpatient with HbA1c >17% (n<5.7%) and a glucose of 260 mg/dL (n 70-99 mg/dL). He was diagnosed with type 2 diabetes mellitus (T2DM), he was started on glipizide. Five months later, he developed DKA with blood glucose >700 mg/dL (n 70-99 mg/dL) and transitioned to insulin therapy with an insulin pump. Two years later, he reported neurological symptoms, including tremors, reduced right arm swing during gait testing, and autonomic dysfunction (erectile dysfunction, diarrhea). Initially misdiagnosed with Parkinson’s disease and started on carbidopa/levodopa without improvement, he was referred to neurology, where elevated GAD-65 antibody titers of 698.2 U/mL (n<5.0 U/mL) confirmed SPS. Despite starting IVIG therapy, his diabetes continued to be managed as T2DM. The patient was later hospitalized for shortness of breath and diagnosed with bilateral pulmonary emboli. During this admission, he developed recurrent DKA with blood glucose levels in the 600s (n 70-99 mg/dL), bilious vomiting, and diarrhea. Laboratory work revealed persistently low C-peptide <0.1 ng/mL (n 0.8-3.5 ng/mL) and negative anti-pancreatic islet cell antibodies. Systemic symptoms, including gastrointestinal dysmotility and thrombotic complications, led to a subsequent diagnosis of systemic sclerosis. Conclusion: This case illustrates the diagnostic challenges of autoimmune syndromes with overlapping features. The patient’s recurrent DKA and neurological symptoms prompted reclassification of his diabetes from T2DM to LADA, a form of type 1 diabetes commonly associated with SPS. Elevated GAD-65 antibody levels confirmed the autoimmune nature of his diabetes and SPS. Additionally, systemic sclerosis, suggested by gastrointestinal and thrombotic manifestations, highlights a broader autoimmune phenotype. This case underscores the need for autoimmune testing, including GAD-65 antibodies and C-peptide. DKA served as a pivotal event in unmasking autoimmune diabetes, SPS, and systemic sclerosis in this patient. Comprehensive evaluation of autoimmune markers is essential in atypical presentations of diabetes to refine diagnosis and guide management. Presentation: Sunday, July 13, 2025