When Type 2 Diabetes Isn't Type 2: Latent Autoimmune Diabetes in a Lean, Highly Physically Active Adult.

Latent autoimmune diabetes in adults (LADA) is frequently misclassified as type 2 diabetes mellitus (T2DM), leading to delayed diagnosis and suboptimal management. We report a lean, highly physically active adult engaged in sustained, high-intensity physical activity as part of his occupation, in his early 70s, with a 30-year history of presumed T2DM who was referred for endocrine evaluation because of persistent glycemic instability despite insulin therapy. He reported frequent symptomatic episodes of both hyperglycemia and hypoglycemia, resulting in significant occupational stress, as maintenance of physical fitness and body weight was essential for continued employment. Hemoglobin A1c (HbA1c) values remained persistently elevated, ranging from 7.8% to 9.6% (reference range: 3.8%-5.6%), with marked glycemic variability and failure to achieve stable control. Given his low body mass index (BMI) of 20 kg/m² (reference range: 18.5-24.9 kg/m²) and pronounced glucose fluctuations, evaluation for autoimmune diabetes was pursued. Laboratory testing demonstrated markedly elevated glutamic acid decarboxylase (GAD65) antibodies (204 IU/mL; reference range <5 IU/mL) and a low C-peptide level (0.54 ng/mL; reference range 1.10-5.50 ng/mL), confirming LADA with advanced beta-cell failure. Management was transitioned from empiric multiple daily insulin injections to a tubeless automated insulin delivery (AID) system integrated with continuous glucose monitoring (CGM). Over longitudinal follow-up, glycemic control improved substantially, with reduced variability and minimal hypoglycemia. At the most recent follow-up, HbA1c was 6.8% (reference range: 3.8%-5.6%). CGM demonstrated a mean glucose of 153 mg/dL, consistent with CGM-derived targets corresponding to an estimated HbA1c <7% (goal <154 mg/dL), with 74% time-in-range (70-180 mg/dL) and less than 2% time below range (<70 mg/dL). This case highlights key clinical clues for recognizing LADA in adults initially labeled as having T2DM and underscores the importance of timely diagnosis and technology-enabled therapy, particularly in individuals with occupationally demanding physical activity.