Endocrine Abstracts

We report five cases of hyperthyroidism with complex management issues, which were successfully treated with iopanoic acid prior to thyroidectomy.

Three patients (cases 1–3) had Graves’ disease; two developed agranulocytosis on carbimazole and one had uncontrolled severe thyrotoxicosis and poor compliance with treatment. Radioiodine was either declined or contraindicated due to radio-protection issues. All patients were rendered euthyroid with iopanoic acid 500 mg BD in combination with propranolol and underwent uncomplicated thyroidectomies.

A further two patients (cases 4 and 5) had Eisenmenger’s secondary to congenital cyanotic heart disease and persistent atrial fibrillation. They developed amiodarone induced thyroiditis (AIT) with no uptake on thyroid scintigraphy suggestive of type 2 AIT and precluding radioiodine therapy. They were resistant or intolerant to treatment with anti-thyroid drugs and steroids and subsequently underwent thyroidectomies after pre-treatment with iopanoic acid 500 mg bd.

In all cases, uncontrolled thyrotoxicosis was prevented and euthyroidism was achieved within an average of 9.8 days (range 2–20) after iopanoic acid treatment.

Iopanoic acid, an iodine-containing oral contrast agent, is a competitive inhibitor of type 1 iodothyronine deiodinase, reducing conversion of T₄ to T₃ in peripheral tissues. Consequently, patients treated with iopanoic acid prior to surgery exhibit a modest reduction in FT₄ levels with a disproportionately larger reduction in its metabolite FT₃, leading to rapid restoration of clinical euthyroidism.

These cases highlight the utility of iopanoic acid in preparing a thyrotoxic patient for thyroidectomy when all other treatments have failed or are unsuitable.