Effects of excess iodine administration on thyroid function in euthyroid patients with a previous episode of thyroid dysfunction induced by interferon-alpha treatment

OBJECTIVE: To determine the effects of pharmacological quantities of iodide (SSKI) on thyroid function in euthyroid patients previously treated with recombinant interferon-alpha (rIFN-α) for chronic vital hepatitis B and C (HCV), a cytokine which may induce thyroid dysfunction. DESIGN: Thyroid function tests were carried out in 16 euthyroid patients, 8 of whom had previously developed thyroid dysfunction during rIFN-α therapy for HCV, before, during and after the administration of 10 drops of saturated solution of potassium iodide (SSKI) (~350 mg iodide). PATIENTS: All 16 patients had been treated in the past with rIFN-α for HCV. Eight patients had developed rIFN-α induced abnormalities in thyroid function (5 inflammatory thyrotoxicosis, 1 Graves' disease, and 2 impaired thyroid organification of iodide) and 8 had not developed thyroid dysfunction. MEASUREMENTS: After baseline serum free T4 (FT4) and free T3 (FT3) concentrations, basal and TRH stimulated TSH concentrations, and TSH-receptor (TSH-R-Ab) and thyroid peroxidase (TPO-Ab) anti-bodies were measured, 10 drops saturated solution of potassium iodide (SSKI, ~350mg iodide) were given daily for 60 days and the above parameters assessed during and after SSKI was discontinued. RESULTS: Five of 8 patients with a previous history of rIFN-α induced thyroid dysfunction developed mild iodide induced abnormalities of thyroid function (subclinical hypothyroidism (slightly elevated basal and TRH stimulated serum TSH concentrations with normal serum FT4 and FT3 concentrations) or hyperthyroidism) compared with the 8 patients who had no previous evidence of thyroid dysfunction during rIFN-α therapy. CONCLUSIONS: In view of the present observations, it is prudent to avoid the administration of excess iodine to euthyroid subjects with a previous episode of thyroid dysfunction during rIFN-α therapy, adding a new group of patients susceptible to iodine induced thyroid disease.