MON-655 A rare case of Stiff-Person Syndrome (SPS) in a young woman with Latent Autoimmune Diabetes in Adult (LADA)

Abstract Disclosure: S. Htoo: None. S. Kalik: None. A. Busta: None. Introduction: Stiff-Person Syndrome (SPS) is a rare autoimmune neurological disorder that is characterized by muscle stiffness and muscle spasms. The estimated prevalence of SPS in the general population is 1 to 2 cases per million. Autoimmune antibodies such as anti-Glutamic acid decarboxylase (GAD) target y-aminobutyric acid (GABA) neurotransmitters, resulting in halting of inhibitory pathways that impair the relaxatory mechanisms of the muscles. Literature has shown few case reports of type 1 Diabetes Mellitus (T1DM) and SPS, however, concomitant occurrence of Latent Autoimmune Diabetes in Adult (LADA) and SPS remains rare. Case: A 39-year-old woman was evaluated for intermittent paresthesia, generalized stiffness in extremities, and episodic spasms of distal muscles. Findings were normal for cranial nerve exam, sensory and motor exam, reflexes and coordination. She had a medical history of latent autoimmune diabetes in adults (LADA), which was discovered during pregnancy 6 years prior. Although initially thought to be gestational diabetes, her insulin requirement remained elevated after delivery, and she had positive GAD antibodies with barely detectable c-peptide level. Her medications included once nightly insulin glargine and subcutaneous semaglutide. She was evaluated for secondary causes of polyneuropathy. Biochemical work-up was normal for thyroid disorders, vitamin deficiencies, other autoimmune and inflammatory disorders. Other laboratory investigations revealed hemoglobin a1c 5.0, serum Glutamic Acid Decarboxylase (GAD) antibody of 38.3 nmol/L (range ≤ 0.02 nmol/L), cerebrospinal (CSF) GAD antibody of 0.39nmol/L (range ≤ 0.02 nmol/L), and c-peptide 0.8 ng/mL (range 1.1 - 4.4 ng/mL). MRI brain and MRI spine were normal. Electromyography (EMG) investigation revealed an abnormal relaxation of agonist and antagonist muscles. A diagnosis of Stiff-person syndrome (SPS) was supported by classic neurological findings, positive GAD antibody on serum and CSF, and characteristics on EMG study. She was treated with 5 days of 1g methylprednisolone and immunoglobulin therapy with observance of mild clinical improvement. Discussion: About 43% of patients with SPS are shown to have T1DM. Although consistent correlation has not been established between the serum anti-GAD titers and disease severity, past cases showed titers levels to be 50-100 times higher than normal in patients with SPS and T1DM. Our patient had LADA serum anti-GAD titer 38.3 nmol/L and she had prominent symptoms of SPS. This demonstrates there could be various levels of severity in SPS. Therefore, we propose larger sale studies are needed to categorize the severity of SPS, to better understand relationship between spectrum of autoimmune diabetes conditions and SPS, and to develop screening guidelines for SPS in patients with both LADA and T1DM. Presentation: Monday, July 14, 2025