Effect of amiodarone on thyroid structure and function

Amiodarone is an effective iodine-rich antiarrhythmic agent that is able to cause thyroid dysfunctions that may substantially worsen health and may be life-threatening. The structure and function of the thyroid was evaluated in 232 patients living in Saint Petersburg who had been receiving amiodarone long (0.6-20 years). During long amiodarone therapy, there were no significant thyroid structural changes; 187 (80%) of the 232 patients had euthyroidism. Thyroid dysfunctions were detected in 45 (20%) patients; amiodarone-induced hypothyroidism (AlH) and amiodarone-induced thyrotoxisis (AIT) were present in 20 (9%) and 25 (119c), respectively. Before amiodarone use, the presence of thyroid peroxidase antibodies significantly increased the risk of AlH (relative risk (RR) 10.0; 95 CI, 8.0-12.0). That of diffuse goiter significantly increased the risk of thyrotoxicosis (RR 5.7; 95% Cl, 4.1-5.9). The serum concentration of thyroid-stimulating hormone receptor antibodies, which had been measured in 23 of the 25 patients with AlT, was used for the differential diagnosis of types I and 2 AIT. As a result, 13 and 10 patients were found to have types 1 and 2 AlT, respectively. The results of other differential diagnostic tests were compared in the groups of patients with types 1 and 2 AlT. Thyroid ultrasonography revealed goiter more frequently in patients with type 1 AlT (10 (779c) of the 13 patients) than in those with type 2 AIT(1 (10%) of the 10 patients; p = 0.01). Color Doppler mapping showed normal or increased thyroid blood flow in all the patients with type 1 AIT and drastically decreased thyroid blood flow in patients with type 2 AIT. In the latter, the serum concentration of free T₄ [43.8±3.4 (23.8-62.8)/ pmol/l and the free T/free T, ratio [8.3±0.6 (5.7-12.3) pmol/t were significantly greater than those in patients with type 1AlT[3I.3± 1.3 (25.1- 40.2) and 5.2+0.4 (3.1- 7.7) pmol/l, respectively (p < 0.05). The h ighest sensitivity and specificity in the differential diagnosis of types 1 and 2 AIT were shown by thyroid ultrasonography (SO and 909c), color Doppler mapping (99 and 99%), as well as free T/free T₃ ratio (86 and 80%), respectively.

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