Radioiodine Therapy for Graves’ Disease Dr. Khalid B. Makhdomi Nuclear Medicine Physician Aga Khan University Hospital, Nairobi

Treatment Antithyroid medications Antithyroid medications Iodine-131 therapy Iodine-131 therapy Surgery Surgery

Antithyroid medications Thionamides. All inhibit the function of TPO, reducing oxidation and organification of iodide. Thionamides. All inhibit the function of TPO, reducing oxidation and organification of iodide. Propylthiouracil inhibits deiodination of T4 to T3. Propylthiouracil inhibits deiodination of T4 to T3.

Antithyroid medications Maximum remission rates are achieved by 18 to 24 months. Maximum remission rates are achieved by 18 to 24 months. The common side effects of antithyroid drugs are rash, urticaria, fever, and arthralgia (1 to 5% of patients). The common side effects of antithyroid drugs are rash, urticaria, fever, and arthralgia (1 to 5% of patients). Rare but major side effects include hepatitis, an SLE-like syndrome, and, most importantly, agranulocytosis (<1%). Rare but major side effects include hepatitis, an SLE-like syndrome, and, most importantly, agranulocytosis (<1%). Relapse rate is over 50%. Relapse rate is over 50%.

Surgery Subtotal thyroidectomy is an option for patients who relapse after antithyroid drugs and prefer this treatment to radioiodine. Subtotal thyroidectomy is an option for patients who relapse after antithyroid drugs and prefer this treatment to radioiodine. Large goitre. Large goitre. Complications - hypoparathyroidism, and damage to the recurrent laryngeal nerves Complications - hypoparathyroidism, and damage to the recurrent laryngeal nerves Recurrence rates Recurrence rates Hypothyroidism is only slightly less than that following radioiodine treatment. Hypothyroidism is only slightly less than that following radioiodine treatment.

Iodine-131 therapy First patient treated with radioiodine (Iodine-130) in First patient treated with radioiodine (Iodine-130) in Iodine-131 was introduced in Iodine-131 was introduced in Iodine-131 Iodine-131 Beta particle emissions Beta particle emissions Range in tissue mm Range in tissue mm

Indications Any patients above a preselected age limit Any patients above a preselected age limit Patients who fail to respond to anti-thyroid drugs Patients who fail to respond to anti-thyroid drugs Prior thyroid or other neck surgery Prior thyroid or other neck surgery Contraindications to surgery such as severe heart, lung or renal disease Contraindications to surgery such as severe heart, lung or renal disease

Contraindications Pregnancy Pregnancy Lactation Lactation Question of malignant thyroid tumour Question of malignant thyroid tumour Age below a preselected age limit such as (possibly) age Age below a preselected age limit such as (possibly) age Patient concerns regarding radiation exposure Patient concerns regarding radiation exposure Severe thyrotoxicosis --- pretreat with antithyroid medications and beta blockers Severe thyrotoxicosis --- pretreat with antithyroid medications and beta blockers Severe ophthalmopathy Severe ophthalmopathy

Iodine-131 therapy Thyroid scan with radioiodine uptake, or technetium scan. Thyroid scan with radioiodine uptake, or technetium scan. Calculation of the Iodine-131 dose. Calculation of the Iodine-131 dose. Pretreatment with antithyroid drugs. Pretreatment with antithyroid drugs. Stopping antithyroid drugs before therapy. Stopping antithyroid drugs before therapy. Ingestion of Iodine-131. Ingestion of Iodine-131. Radiation precautions. Radiation precautions.

Procedure Thyroid Scan Thyroid Scan Dose determination Dose determination Calculated dose µCi/gm Calculated dose µCi/gm Fixed dose Fixed dose Higher doses for solitary toxic nodule and Higher doses for solitary toxic nodule and toxic multi-nodular goitre toxic multi-nodular goitre Therapy Therapy Preparation Preparation Precautions Precautions No significant effect till 2-3 weeks No significant effect till 2-3 weeks Maximum effect by 3-4 months Maximum effect by 3-4 months

Factors Affecting Treatment Iodine uptake Iodine uptake Size of goitre Size of goitre Length of time I-131 is retained in the gland Length of time I-131 is retained in the gland Homogeneity of distribution within the gland Homogeneity of distribution within the gland Radiosensitivity of thyroid cells Radiosensitivity of thyroid cells Drug interactions Drug interactions Antithyroid medications Antithyroid medications Thyroid hormones Thyroid hormones Topical Iodine Topical Iodine Radiographic contrast agents Radiographic contrast agents Amiodarone Amiodarone

Side Effects Transient sore throat or mild dysphagia Transient sore throat or mild dysphagia Exacerbation of ophthalmopathy Exacerbation of ophthalmopathy Radiation thyroiditis Radiation thyroiditis No increase in incidence of No increase in incidence of Thyroid cancer Thyroid cancer Leukemia or other malignancies Leukemia or other malignancies No harmful effect upon No harmful effect upon Health of progeny Health of progeny Fertility Fertility Reproductive history Reproductive history

Empirical dual dose therapy 15 and 20 mCi 15 and 20 mCi Number of patients Number of patients Follow-up years Follow-up years Outcome Outcome Hypothyroid % Hypothyroid % Euthyroid % Euthyroid % No response --- 8% No response --- 8%

Conclusion Radioiodine therapy for hyperthyroidism Radioiodine therapy for hyperthyroidism Effective Effective Simple Simple Safe Safe Cheap Cheap Treatment of choice Treatment of choice Patients above 30 Patients above 30 Patients with medical complications Patients with medical complications Relapse after medical therapy Relapse after medical therapy Recurrence after surgery Recurrence after surgery