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Use of Adjunctive Potassium Iodide after Radioactive Iodine (¹³¹I) Treatment of Graves' Hyperthyroidism^*

DOUGLAS S. ROSS, GILBERT H. DANIELS, PAUL DE STEFANO, FARAHE MALOOF and E. CHESTER RIDGWAY

Thyroid Unit, Department of Medicine, Massachusetts General Hospital, and Harvard Medical School Boston, Massachusetts 02114

Address requests for reprints to: Dr. Douglas S. Ross, Thyroid Unit, Massachusetts General Hospital, Boston, Massachusetts 02114.

One hundred and nineteen patients with Graves' hyperthyroidism who were treated with ¹³¹I alone or ¹³¹I followed by potassium iodide (¹³¹I+KI) were studied retrospectively. Patients in both groups who required only a single dose of ¹³¹I for successful treatment of hyperthyroidism had similar age, gland size, 24-h radioactive iodine uptake, pretreatment serum T₄ concentrations, and radioactive iodine treatment dose. Seven weeks after ¹³¹I, mean serum T₄ concentrations were 12.3 ± 6.1 µg/dl (mean ± SD) in patients who received ¹³¹I alone and 8.0 ± 3.9 µg/dl in patients who received ¹³¹I+KI (P < 0.001). Sixty percent of the patients who received ¹³¹I+KI and remained euthyroid 1 yr after ¹³¹I treatment developed documented transient hypothyroidism while receiving KI (serum T₄, 1.4 ± 0.9 µg/dl). Patients with transient hypothyroidism receiving KI had larger estimated thyroid gland weights when hypothyroid than patients whose hypothyroidism was permanent (32 ± 6 vs. 16 ± 11 g; P < 0.001). The overall incidence of hypothyroidism 1 yr after treatment with ¹³¹I was 58% in each of the two groups. Sixteen percent of each group were not successfully treated by a single dose of ¹³¹I and required further therapy. Adjunctive KI effectively treated thyrotoxicosis more rapidly than ¹³¹I alone without adversely affecting outcome at 1 yr; however, patients taking KI more often develop transient hypothyroidism.

^* This work was supported in part by NIH Research Grants AM-16791 and AM-07028.

Current address: Matthew Thorton Health Plan, 591 West Hollis Street, Nashua, New Hampshire 03062.

Received December 3, 1982.

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