Iodine-induced hyperthyroidism due to nonionic contrast radiography in the elderly

To identify the number of cases of hyperthyroidism that followed the performance of contrast radiography in elderly patients at a geriatric hospital in a non-iodine-deficient area and to determine the clinical course of the condition.

All patients over a 20-month period with biochemical hyperthyroidism (plasma free thyroxine level greater than 25.0 pmol/L and thyroid-stimulating hormone level less than 0.10 IU/L) were identified. Clinical features of hyperthyroidism and exposure to nonionic contrast media radiographs within the previous 12 months were sought. Follow-up extended from 6 to 22 months.

A total of 28 patients with hyperthyroidism (aged 70 to 96 years) were identified. Seven patients (25%) had documented biochemical development of hyperthyroidism (five) or subsequent hyperthyroidism (two) 3 to 8 weeks after nonionic contrast media radiography. The four patients who underwent scanning had a multinodular thyroid, and thyroid antibodies were not detected in five of five patients. Although the condition appeared self-limited and six of six patients were euthyroid after 18 months, the condition was not benign; progress and recovery were adversely affected by hyperthyroidism. Four patients had a good response to treatment with an antithyroid drug (carbimazole).

Iodine-induced thyrotoxicosis following contrast radiography was found in 7 of 28 cases of hyperthyroidism seen at a geriatric hospital. Although the condition appears ultimately self-limited, pharmacologic control of severe clinical features may be required. The frequency of this condition in a non-iodine-deficient area appears related to the more common occurrence of autonomous thyroid nodules in the elderly. Because performance of contrast radiography is more common in this age group, the recognition and treatment of iodine-induced thyrotoxicosis are of increasing clinical importance.