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

Clin Endocrinol (Oxf). 1999 Feb;50(2):197-202. doi: 10.1046/j.1365-2265.1999.00635.x.


Objective: To investigate the long-term effects of radioiodine (131I) 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 131I.

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: 131I treatment (3.7 MBq/g thyroid tissue corrected to a 100% 24-h 131I uptake) was given as a single dose in 53 patients; six needed two doses and another three were given 3-5 131I treatments. The median initial dose was 310 MBq (140-666) and the median total dose was 332 MBq (148-1576). In patients receiving one 131I 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 131I treatment. Patients without antithyroid pretreatment, receiving one 131I 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 131I (n = 14) euthyroidism was achieved after a median of 12 months (0.75-24) after 131I treatment. Hypothyroidism developed in five patients (8%) after a median of 36 months (6-60) after 131I treatment.

Conclusion: A cure-rate of 75% within 3 months is seen when treating autonomous solitary toxic thyroid nodules with 131I. 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Female
  • Follow-Up Studies
  • Humans
  • Iodine Radioisotopes / therapeutic use*
  • Male
  • Middle Aged
  • Prospective Studies
  • Thyroid Gland / pathology
  • Thyroid Gland / physiopathology
  • Thyroid Gland / radiation effects*
  • Thyroid Nodule / pathology
  • Thyroid Nodule / physiopathology
  • Thyroid Nodule / radiotherapy*
  • Time Factors
  • Treatment Outcome


  • Iodine Radioisotopes