EFFECTS OF EXCESS IODINE ADMINISTRATION ON THYROID-FUNCTION IN EUTHYROID PATIENTS WITH A PREVIOUS EPISODE OF THYROID-DYSFUNCTION INDUCED BYINTERFERON-ALPHA TREATMENT

OBJECTIVE To determine the effects of pharmacological quantities of io dide (SSKI) on thyroid function in euthyroid patients previously treat ed with recombinant interferon-alpha (rIFN-alpha) for chronic viral he patitis B and C (HCV), a cytokine which may induce thyroid dysfunction . DESIGN Thyroid function tests were carried out in 16 euthyroid patie nts, 8 of whom had previously developed thyroid dysfunction during rIF N-alpha therapy for HCV, before, during and after the administration o f 10 drops of saturated solution of potassium iodide (SSKI) (similar t o 350 mg iodide). PATIENTS All 16 patients had been treated in the pas t with rIFN-alpha for HCV, Eight patients had developed rIFN-alpha ind uced abnormalities in thyroid function (5 inflammatory thyrotoxicosis, 1 Graves' disease, and 2 impaired thyroid organification of iodide) a nd 8 had not developed thyroid dysfunction. MEASUREMENTS After baselin e 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) antibodies were measured, 10 drops saturated solu tion of potassium iodide (SSKI, similar to 350mg iodide) were given da ily for 60 days and the above parameters assessed during and after SSK I was discontinued, RESULTS Five of 8 patients with a previous history of rIFN-alpha induced thyroid dysfunction developed mild iodide induc ed abnormalities of thyroid function (subclinical hypothyroidism (slig htly elevated basal and TRH stimulated serum TSH concentrations with n ormal serum FT4 and FT3 concentrations) or hyperthyroidism) compared w ith the 8 patients who had no previous evidence of thyroid dysfunction during rIFN-alpha therapy. CONCLUSIONS In view of the present observa tions, it is prudent to avoid the administration of excess iodine to e uthyroid subjects with a previous episode of thyroid dysfunction durin g rIFN-alpha therapy, adding a new group of patients susceptible to io dine induced thyroid disease.