Abstract Disclosure: F.L. Thelmo: None. M. Murugesh: None. B. Simon: None. Introduction: The autoantibody GAD (anti-glutamic acid decarboxylase) is highly associated with Type 1 diabetes (T1DM) and Latent Autoimmune Diabetes in Adulthood (LADA). If GAD is detected before the onset of overt diabetes, typically 80% of patients with abnormal glucose tolerance progress to insulin deficiency and the need for insulin treatment after 5 years.[1] Stiff Person Syndrome (SPS) is also associated with GAD antibodies, but in SPS, the GAD antibodies are believed to be different epitopes that target GABA production in neuromuscular pathways. We present a case of presumed LADA that did not progress for 30 years, with progressive neurologic symptoms leading to a diagnosis of SPS in later adulthood.Case: A 52-year-old female presented for evaluation of T1DM and worsening neuropathies. She had a long history of prediabetes, with mildly elevated glucose values noted on labs since her early twenties. There was no family history of T1DM or autoimmune conditions. Six years ago, she sought endocrine evaluation. HgbA1c values were 6.1 to 6.6%. Intermittent use of continuous glucose monitoring (CGM) revealed post-prandial hyperglycemia up to 180mg/dL, occasionally (but rarely) exceeding 200mg/dL. She recalls being told that she had positive antibodies (unclear which ones tested) and given a diagnosis of T1DM. She declined insulin and maintained glycemic control with carbohydrate restriction and exercise; there were no episodes of diabetic ketoacidosis. She then developed neurologic symptoms: fullness, tightness and bloating in the abdomen (diagnosed with gastroparesis on scanning) and after a COVID 19 booster in 2021, muscle spasms in the legs and back with worsening abdominal tightness. At the time of her current presentation, A1C was 6.4%, glycated albumin was 14.4% (prediabetes range 13.6 - 15.5%) and CGM time in range was 99%. A non-fasting C-peptide was 3.6 ng/mL (1.1- 4.4ng/mL) with glucose of 119 mg/dL. Repeat antibody testing revealed undetectable IA-2 and ZnT8 antibodies, but GAD was grossly elevated at 1,015.3 U/mL. Given the unusually high GAD titer, SPS was suspected, and this diagnosis was confirmed on referral to neurology. The patient was advised to liberalize diet and will be monitored with HgbA1c and serial C-peptide levels to assess progression in the future. Discussion: While high GAD antibody levels are associated with progression to insulin dependence in adults with LADA, in SPS the GAD titers tend to be even higher2. The presence of only one auto-antibody for T1DM (and not multiple), long-standing non-progressive hyperglycemia, and normal C-peptide pointed away from autoimmune diabetes being the etiology for mild glucose intolerance in this patient. If neurologic symptoms are present, high GAD should prompt the evaluation for other syndromes associated with GAD antibody epitopes such as SPS. Presentation: 6/2/2024
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