Treatment of thyrotoxicosis — the current position Part II: Drug therapy and thyroidectomy

Summary

Antithyroid drugs such as carbimazole and propylthiouracil prevent iodination of thyroglobulin and reduce hormone formation, storage and secretion. Carbimazole is the most favoured and should be given 8-hourly, initially in daily doses of 45 to 60 mg. decreasing to 15 mg. or less when the thyrotoxicosis is controlled. Patients with mild thyrotoxicosis and a small goitre and satisfactory response should have carbimazole for 18 months. The decision to continue antithyroid drugs for longer than 6 months may be easier if a 20-minute radioiodine uptake is suppressed by T3 given for a week or more (T3 suppression test), although this test of remission is not infallible.

Patients with large glands, and who are difficult to bring under control with drugs, should have an operation or radioactive iodine (¹³¹I) therapy depending on age and fertility. Likewise people who have a relapse after stopping drug treatment (and this may be increased by iodide) can have another course or alternatively operation or radioiodine therapy.

In general, antithyroid drugs are very safe; occasionally, (1 in 30) a maculopapular rash is seen or the patient has nausea. A granulopenia is very rare, never complete, occurs suddenly and is nearly always reversible if drugs are stopped. Potassium per chlorate is only used when other treatment is not feasible since it might cause aplastic anaemia. Studies with ³⁵S labelled antithyroid drugs show that they differ in distribution, and rate and mode of metabolism.

Partial thyroidectomy is reserved for patients with obvious goitres, severe or relapsing thyrotoxicosis and always provided there is a skilled surgical team and an agreeable and fit patient. In experienced hands the outcome is good, but occasionally the patient is left with hoarseness, or parathyroid insufficiency, or a bad scar. There is also a risk of hypothyroidism and sometimes patients relapse. The incidence of complications is related to many factors but it is known that the more evidence there is of thyroid autoimmunity the higher the risk of post-operative hypothyroidism; and there is an inverse relationship between risk of hypothyroidism and recurrence, probably related to the amount of tissue resected.

Note: This review article is in three parts. Part 111: Radioiodine therapy. Special considerations.

Key words: :

• Hyperthyroidism
• drug therapy
• radiotherapy
• thyroidectomy

Notes

Note: This review article is in three parts. Part 111: Radioiodine therapy. Special considerations.