Levothyroxine and insulin requirement in autoimmune polyglandular type 3 syndrome: a real-life study

Purpose: To evaluate factors influencing the insulin and levothyroxine requirement in patients with autoimmune polyglandular syndrome type 3 (APS-3) vs. patients with type 1 diabetes mellitus (T1DM) and autoimmune hypothyroidism (AH) alone, respectively. Methods: Fifty patients with APS-3, 60 patients with T1DM and 40 patients with AH were included. Anthropometric, clinical and biochemical parameters were evaluated in all patients. Insulin requirement was calculated in patients with APS-3 and T1DM, while levothyroxine requirement was calculated in APS-3 and AH. Results: Patients with APS-3 showed higher age (p = 0.001), age of onset of diabetes (p = 0.006) and TSH (p = 0.004) and lower total insulin as U/day (p < 0.001) and U/Kg (p = 0.001), long-acting insulin as U/day (p = 0.030) and U/kg (p = 0.038) and irisin (p = 0.002) compared to T1DM. Patients with APS-3 had higher waist circumference (p = 0.008), duration of thyroid disease (p = 0.020), levothyroxine total daily dose (p = 0.025) and mcg/kg (p = 0.006), triglycerides (p = 0.007) and VAI (p = 0.010) and lower age of onset of thyroid disease (p = 0.007) than AH. At multivariate analysis, levothyroxine treatment and VAI were associated with insulin and levothyroxine requirement in APS-3, respectively. VAI was independently associated with insulin requirement in T1DM. Circulating irisin levels were independently associated with levothyroxine requirement in AH. Conclusion: Patients with APS-3 show lower insulin requirement and higher levothyroxine requirement than T1DM and AH alone, respectively. Levothyroxine treatment and VAI affect insulin and levothyroxine requirement, respectively, in APS-3. In T1DM, adipose tissue dysfunction, indirectly expressed by high VAI, is associated with an increased insulin requirement, while circulating irisin levels influence the levothyroxine requirement in AH.