Amiodarone-induced thyroid dysfunction masking a resistance to thyroid hormone diagnosis in an Octogenarian with cardiac manifestations

Background

Resistance to thyroid hormone (RTH) syndrome is a rare clinical condition and manifests biochemically as persistent hyperthyroxinemia with unsuppressed thyroid-stimulating hormone (TSH) levels. Amiodarone-induced thyroid dysfunction being reviewed in relation to a co-existing RTH syndrome diagnosis does not exist in the literature as much as we are aware, hence this case report.

Case report:

A present-day 88-year-old female was reviewed at an endocrinology clinic a decade prior, upon referral by managing cardiologists for an evaluation of abnormal thyroid function test (thyroid Stimulating Hormone (TSH) level of 32 mU/L (reference: 0.4–5 mU/l), free T4 of 13 pmol/L (reference: 9–19 pmol/l) and a free T3 of 5.7 pmol/L (2.4–6pmol/l), complicating amiodarone use in the management of her refractory atrial fibrillation. She had undergone two electrical cardioversions at the time and had a thyroid ultrasound scan (US) revealing a multinodular goitre. Amiodarone was subsequently withdrawn from her treatment by the reviewing endocrinologist at the time. Follow-up care of this patient culminated in a genetic sequence testing that confirmed an underlying RTH diagnosis (heterozygous pathogenic THR beta variant: c.1312C > T p. (Arg438Cys)) in this patient a decade afterward.

Conclusion

In a setting of hyperthyroxinemia and unsuppressed thyroid-stimulating hormone level, RTH syndrome should be suspected. Genetic analysis for this condition should then be suggested. Underlying thyroid conditions should be considered in patients with persistent cardiac arrhythmias. Baseline thyroid function tests should be considered in medications with thyroid side effects.