A Case of Persistent Hyperglycemia: Autoimmune Link Between Hashimoto’s Thyroiditis and Latent Autoimmune Diabetes in Adults

Latent autoimmune diabetes in adults (LADA), also known as type 1.5 diabetes, is an autoimmune diabetes that shares genetic, immunological, and clinical features with type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) and is commonly misdiagnosed as type 2 diabetes. Thyroid disease in patients with LADA was estimated to be 17.7%. We are reporting a case of Hashimoto's thyroiditis (HT) in an obese patient having hyperglycemia with poor response to regular management. We reported this case as a reminder that the presence of an autoimmune condition in a patient with hyperglycemia, autoimmune diabetes, must be considered. A 40-year-old female with a body mass index of 35.2 kg/m² complains of fatigability and exercise intolerance. Her HbA1c was 7.9; she was first diagnosed with T2DM and started on the oral hypoglycemic agent metformin. Her HbA1c increased despite her admitting that she was adherent to her medications and the dietary regimen. She reported anterior neck swelling. The thyroid ultrasound showed a heterogeneous texture of the thyroid gland. Anti-thyroid peroxidase antibody titer and anti-thyroglobulin antibody titer were high. Her anti-TSH receptor antibody titer was within the normal range. Thus, she was diagnosed with autoimmune HT and started on thyroxine. Both parents had T2DM, and she was never admitted to the hospital with ketoacidosis. Failure to control her diabetes, along with the recent diagnosis of autoimmune HT, raises the suspicion of LADA. Her anti-glutamic acid decarboxylase (GAD) antibody then came back positive, and her C-peptide level was low. She was shifted to an insulin basal and bolus regimen, and her last HbA1c was 5.7. The case highlights the importance of considering LADA in patients with poor glycemic control despite standard T2DM therapy, especially when autoimmune diseases are present: positive anti-GAD antibodies, low C-peptide, and improved outcomes with insulin support the diagnosis. Early detection is crucial for effective management and preventing disease progression.