Exploring the Muscle-to-Fat Ratio of Pediatric Patients with Thyroid Disorders and Its Interaction with Thyroid Function and Metabolic Syndrome Components

Background/Objectives: The standard evaluation of children and adolescents suspected of having thyroid disorders consists of anthropometric measurements. Body composition features provide additional information for enhanced therapeutic management. We explored the muscle-to-fat ratio of pediatric patients referred for thyroid disorders and its interaction with thyroid function and metabolic syndrome components. Methods: This retrospective cross-sectional study consisted of 147 pediatric subjects (ages 5-19 years) diagnosed with childhood-onset thyroid disorders treated at a tertiary medical center. Sociodemographic, clinical and laboratory data [thyroid-stimulating hormone (TSH), free T4 (FT4), and lipid profile] were extracted from the electronic medical records. Body composition was measured using bioimpedance analysis (Tanita MC-780 MA and GMON Professional Software). Body mass index (BMI), appendicular muscle mass (ASMM), and muscle-to-fat ratio (MFR) were converted to z-scores. Results: The diagnoses included Hashimoto thyroiditis (30.6%), subclinical hypothyroidism (26.5%), congenital hypothyroidism (21.7%), and Graves' disease (21%). Based on BMI z-scores, 31.3% of the cohort was overweight or obese. The TSH levels were positively correlated with the BMI z-scores (r = 0.238, p = 0.005) and negatively with the MFR z-scores (r = 0.215, p = 0.012). The ASMM z-scores were negatively associated with the FT4 levels (r = -0.255, p = 0.003). Dyslipidemia was prevalent. TSH was correlated with LDL cholesterol (r = 0.472, p < 0.001) and triglycerides (r = 0.232, p = 0.05). Conclusions: Elevated thyroid-stimulating levels were linked to higher BMI and lower MFR levels. Our findings on the relationship between thyroid function and lipid profile underscore the necessity of optimizing thyroid balance and implementing targeted lifestyle interventions to improve body composition in young patients with thyroid disorders.