Efficacy of a fixed low dose of radioactive iodine in the treatment of Graves' disease in Sub-Saharan Africa.

Objective: Graves' disease represents 60%-90% of all causes of thyrotoxicosis in different regions of the world. Thyrotoxicosis contributes approximately 66% to thyroid disorders in South Africa and of those Graves' disease contributes about 34%. In most Sub-Saharan African countries, Graves' disease is managed mainly with medical treatment, due to a lack of or poor access to other means of treatment. Despite the primary use of anti-thyroid drugs (ATD) in the management of Graves' disease, the use of radioactive iodine (RAI) is required in many patients, especially in cases where ATD are contraindicated, or in patients who have failed ATD treatment and are poor surgical candidates. There is no consensus on the best method for deciding on how much activity of radioiodine to administer to patients with Graves' disease, that is, whether to use a calculated dose, or an empirical or fixed dose for RAI. The standardized fixed dose is particularly helpful in under-resourced areas or centres with few nuclear physicians and high patient loads. However, little is known about the efficacy of the fixed dose compared to the calculated or empirical dose methods. The purpose of this retrospective observational study was to assess the efficacy of a fixed low dose of radioiodine-131 (¹³¹I) in the treatment of Graves' disease.

Subjects and methods: Patients treated with a fixed dose of 10mCi between the periods of 2014 to 2017 were evaluated for treatment response after each dose of RAI. Outcome of therapy was evaluated at 3 monthly follow-up using biochemical markers: thyroid stimulating hormone (TSH), total free thyroxine (fT4), and or triiodothyronine (T3), and the presence or absence of clinical symptoms of thyrotoxicosis. According to their response to RAI therapy, patients were classified as responders (if they became euthyroid or hypothyroid), non-responders (if they failed to achieve euthyroidism or hypothyroidism at 6 months) and complete treatment failure (if no response was present within 18 months after two or three fixed low doses of RAI). Percentage uptake, baseline fT4 and patient age were compared according to treatment response.

Results: Our cohort included 111 patients, 95 (86%) females and 16 (14%) males, with a mean age of 41.9 years. Treatment was successful after the first dose in 89.2% of cases (27.0% euthyroid; 62.2% hypothyroid), with 10.8% requiring a second dose, and only a single patient who remained hyperthyroid after that second empiric dose. Statistical analysis demonstrated that a high percentage thyroid uptake was associated with treatment failure, whereas a low percent thyroid uptake was associated with a good treatment response (P=0.0048). We found no significant difference in FT4 levels or age, between hyperthyroid and non-hyperthyroid (euthyroid or hypothyroid) groups post initial RAI therapy (P=0.5 and P=0.96, respectively).

Conclusion: The use of a low fixed/empiric radioiodine activity for hyperthyroidism due to Graves' disease performed well in our setting with a nearly 90% response rate achieved after a single dose of 10mCi. Justification for higher activity should be specified, and this method of determining the optimal dose of RAI therapy may be beneficial in resource constrained settings with high patient volumes.