Resistance to thyroid hormone (RTH) is a rare, autosomal dominant disorder characterised by a reduced sensitivity of peripheral tissues to thyroid hormone. Thyroid function testing shows elevation of free T4 and T3 with non suppressed TSH levels.
Vascular function in these patients has not been fully evaluated. We have studied central arterial stiffness in a cohort of RTH patients, comparing them with age and sex matched controls.
Method: Pulse wave analysis (PWA) was performed in 9 patients with RTH (5M: 4F, mean age 35.8±17.5 yrs) using applanation tonometry. Using PWA indices of arterial stiffness were calculated including augmentation index (AI) and AI corrected for heart rate (AIc). Each patient had a confirmed genetic mutation and none of the patients had any co-existing conditions such as diabetes mellitus, hypertension or heart disease.
Results: Mean T4 level in RTH patients vs controls was 25.7±4.8 pmol/L vs 14.4±1.3, P<0.0001. [NR 9.823.1 pmol/L]. Median TSH level was 1.9 mU/L [Range 0.610.3 mU/L] vs 1.5 mU/L [Range 0.82.4] [NR 0.355.5 mU/L], P=ns.
Non-significantly elevation of AI and AIc was demonstrated in patients compared with controls. When the patient group divided according to age into Group A (age 1839 yrs) and Group B (ages 4065 yrs) and compared with controls there were significant differences. The AI in group A was 2.5±5.3% vs −14.3±4.0% in controls, P<0.05.AIc was also elevated 3.75±5.1% vs −16.3±5.8%. In group B AI was 28.4±2.2% vs 17.6±3.7% in controls (P<0.05) and AIc was 28.6±3.7% vs 16.4±4.0% (P<0.05).
Conclusion: Patients with RTH have evidence of increased central arterial stiffness compared with age and sex matched controls when compared within similar age groups.