Lean body mass-based levothyroxine replacement in young athyrotic patients with differentiated carcinoma of thyroid

Abstract

Objective:The objective of this study was to optimize dose of levothyroxine (LT4) based on lean body mass (LBM) in young athyrotic patients with differentiated carcinoma of thyroid (DCT) which has not been properly addressed in Bangladesh before.Materials and Methods:Sixty patients with DCT (age, range: 20-39 years) having total thyroidectomy followed by radioiodine ablative therapy (RIT) and 23 euthyroid volunteers were recruited. Clinical, biochemical parameters were obtained from all patients after 2 months of RIT and on LT4 replacement at a dose of 200 μg/day as first follow up visit and also from control subjects. Then 60 patients were divided into two groups consisting of 30 patients each. Patients of Group-I received LT4 replacement based on LBM measured by dual energy X-ray absorptiometry (DXA) and Group-II continued LT4 replacement in conventional dose. Patients of both groups were assessed again for same parameters at 6 to 12 months at the second visit.Results:Optimized dose of LT4 based on LBM by DXA (131 ±23 μg/day) significantly reduced thyroid hormones and kept thyroid stimulating hormone (TSH) in expected levels in patients of Group-I at the second visit compared to patients of Group-II who continued conventional LT4 dose (200 μg/day). Hyperthyroid symptom scale (HSS) was significantly reduced to 2 ± 1 in patients of Group-I but not in patients of Group-II, HSS, 8 ±1 (P > 0.001).Conclusion:Optimization of LT4 dose based on LBM can avoid chronic exposure of mild excess of thyroid hormone in young patients with low risk DCT.

Comparison of the Efficacy of Levothyroxine Suppression Dose Computed Based on Actual Body Weight vs. Lean Body Mass among Differentiated Thyroid Cancer Patients: A Randomized Controlled Trial

“…Different studies 8 , 9 have suggested that LBM has been shown to be superior to other measures of body size for dosage of many drugs. 8 , 9 LBM equals the total weight of a person’s bone and muscles minus their fat weight. 10 Pharmacokinetic parameters are mostly dependent on LBM and most metabolic processes occur within this body compartment.…”

“…In this study, LBM was computed based on validated anthropometric prediction equations for estimation of LBM in Indian men and women 6 in contrast to a few studies 7 - 9 where LBM was measured by dual energy X-ray absorptiometry (DEXA). The use of this prediction equation was simple, reproducible, noninvasive, and inexpensive compared to the estimation of LBM by MRI or DEXA.…”

“…This finding was in agreement to a previous study11 which showed that estimates of LBM based on routine anthropometric measurements were no better in predicting LT4 requirement in achieving TSH goals after total thyroidectomy than body weight. Moreover, another study even states that although total daily requirements of LT4 are related to LBM, there are unexplained differences such as ethnicity 9 which occur among individuals of the same age and body size even in the absence of functioning thyroid tissue.…”