Long‐term effect of radioactive iodine on thyroid function and size in patients with solitary autonomously functioning toxic thyroid nodules

Abstract

OBJECTIVE: To investigate the long‐term effects of radioiodine (131 I) on thyroid function and size in patients with a solitary toxic thyroid nodule. DESIGN: Prospective study of patients treated for a solitary autonomous toxic nodule, followed by evaluation of thyroid volume and function. PATIENTS: Sixty‐two consecutive patients followed for a minimum of 12 months (range 12–168, median 60). Seventeen patients received antithyroid drug treatment before 131 I. MEASUREMENTS: Standard thyroid function variables and ultrasonically determined thyroid volume before as well as 0.75, 1.5, 3, 6 and 12 months after treatment, and then once a year were investigated. RESULTS: 131 I treatment (3.7 MBq/g thyroid tissue corrected to a 100% 24‐h 131 I uptake) was given as a single dose in 53 patients; six needed two doses and another three were given 3–5 131 I treatments. The median initial dose was 310 MBq (140–666) and the median total dose was 332 MBq (148–1576). In patients receiving one 131 I treatment (n = 53) the total thyroid volume decreased significantly from a median of 40 ml (range 19–77) to 24 ml (8–50) within 3 months. This represented a median reduction of 35%. A further significant decrease was seen after 24 months to a total reduction of 45%. In patients given more than one dose the thyroid volume was reduced from a median of 45 ml (19–104) before treatment to 30 ml (14–50) after a follow‐up of 60 months (9–132) after the last 131 I treatment. Patients without antithyroid pretreatment, receiving one 131 I treatment (n = 39) became euthyroid after a median of 1.5 months (0.75–9) after treatment. Seventy‐five per cent were euthyroid within 3 months. In patients pretreated with antithyroid drugs and treated with one dose of 131 I (n = 14) euthyroidism was achieved after a median of 12 months (0.75–24) after 131 I treatment. Hypothyroidism developed in five patients (8%) after a median of 36 months (6–60) after 131 I treatment. CONCLUSION: A cure‐rate of 75% within 3 months is seen when treating autonomous solitary toxic thyroid nodules with 131 I. The thyroid volume is reduced by 35% within 3 months and 45% after 2 years. Side‐effects are few and consist of hypothyroidism in less than 10% with a median follow‐up of 5 years. This treatment should be regarded as the standard treatment for this condition until prospective comparisons with surgery and ethanol injection therapy have been performed.