SAT-617 Potential Utility of the Mixed Meal Test for Differential Diagnosis of Partial Lipodystrophy from Common Type 2 Diabetes and Truncal Obesity

Background: Better clinical tools are needed to improve the differential diagnosis of partial lipodystrophy (PL) from type 2 diabetes (DM) with truncal obesity. Here, we investigated differences in metabolic parameters during a mixed meal test in PL and DM patients to determine if this test may have a role in this regard. Methods: We retrospectively evaluated data collected from 17 PL patients (4M/13F, ages 12-64) and 20 DM patients (13F/7M, ages 24-72) with truncal obesity, who also had nonalcoholic fatty liver disease. All patients underwent a Mixed Meal Test (MMT) with 474 ml of Optifast (320 kcal, 50% carbs, 15% fat, and 35% protein). Blood was collected before and at 30, 60, 90, 120, and 180 minutes post-meal to measure glucose, insulin, free fatty acids (FFA), triglycerides, inflammatory markers, GIP, GLP-1, PYY, and Ghrelin. All samples of the same cohort were run at the same time in duplicates and results were averaged. Mixed linear models were constructed to compare PL and DM cohorts taking into account within-subject effects. Data were controlled for BMI, sex and age, and glucose when necessary. Results: Patients with PL had higher glucose and triglyceride levels throughout the MMT at all-time points (p < 0.05). While the glucose levels showed an increase and subsequent decrease, the triglyceride levels remained flat throughout the test in both groups. Free fatty acid levels were suppressed compared to baseline during the test, but PL patients had significantly higher FFA from time 30 to time 180 (p < 0.05) and tended to suppress less. While controlling for the differences in glucose levels, GIP levels displayed a large peak at time 30 min in both groups but were significantly higher over the course of the test in the PL group (AUC: 32542, pg/mL x min (20528-57728) vs. 3343 pg/mL x min (1728-4498), p < 0.05). In contrast, GLP-1 levels (also peaking at time 30 min in both groups), were significantly lower in PL throughout the test (AUC: 3017 pg/mL x min (2309-6051) vs. 28387 pg/mL x min (20422-36045), p < 0.05). Ghrelin and PPY levels did not differ significantly between the two groups. Interpretation/Conclusion: PL patients displayed more profound hyperglycemia and impaired suppression of FFAs. Interestingly, PL patients did not show substantial increases in triglyceride levels during MMT. There was a striking difference in the incretin responses between the two populations despite controlling for glucose, suggesting that MMT may have a role in differential diagnosis PL. Also, altered incretin response should be investigated as a contributor to metabolic perturbations and pathophysiology of PL.