[Ultra-sensitive TSH levels: an aid in the screening for amiodarone-induced thyroid dysfunction]

Abstract

Amiodarone modifies thyroid hormone secretion and hypothyroidism occurs in some cases. The latter diagnosis is often difficult and is of particular importance in these patients as it may have serious consequences for the heart. Early diagnosis is therefore essential but difficult because of the induced hyperthyroxinemia with maintenance of euthyroidism and a hypotriiodothyronemia. The diagnostic performance of an ultrasensitive method of measuring TSH (TSH-U), capable of distinguishing hyper and euthyroidism were compared with standard thyroid function tests and TSH stimulation with TRH in 50 patients treated with amiodarone. Only 6 of the 14 patients with hyperthyroxinaemia had TSH-U values in the hyperthyroid range: only one of these patients had an increased triiodothyronine. In 2 cases the THS-U was low but the T4L was normal. In 4 patients, increased TSH-U allowed diagnosis of latent or patent hypothyroidism. There was a close correlation between results of the TRH stimulation test and those of the TSH-U in all cases. This test may therefore be used as an initial screening test for thyroid dysfunction in patients on amiodarone and is simple, reliable and relatively cheap to perform. It makes it unnecessary to measure all thyroid hormonal parameters and the TRH test simultaneously.