Principles of treatment of thyrotoxicosis

Non-specific measures are rest and sedation and in established thyrotoxicosis should be used only in conjunction with spe- cific measures, i.e. the use of antithyroid drugs, surgery and radioiodine.

ANTITHYROID DRUGS

Those in common use are carbimazole and propylthiouracil. Antithyroid drugs are used to restore the patient to a euthyroid state and to maintain this for a prolonged period in the hope that a permanent remission will occur, i.e. that production of thyroid-stimulating antibodies (TSH-RAb) will diminish or cease. Antithyroid drugs cannot cure a toxic nodule. The overactive thyroid tissue is autonomous and recurrence of the hyperthyroidism is certain when the drug is discontinued.

● Advantages. No surgery and no use of radioactive materials.

● Disadvantages. Treatment is prolonged and the failure rate is at least 50%. The duration of treatment may be tailored to the severity of the toxicity, with milder cases being treated for only 6 months and severe cases for 2 years before stopping therapy.

SURGERY

In diffuse toxic goitre and toxic nodular goitre with over- active internodular tissue, surgery cures by reducing the mass of overactive tissue by reducing the thyroid below a criti- cal mass. After subtotal thyroidectomy the patient should return to a euthyroid state, albeit after a variable period of hypothyroidism. There are however, the long-term risks of recurrence and eventual thyroid failure. In contrast total/ near total thyroidectomy accepts immediate thyroid failure and lifelong thyroxine replacement to eliminate the risk of recurrence and simplify follow-up. Operation may result in a reduction in TSH-RAb. In the autonomous toxic nodule, and in toxic nodular goitre with overactive autonomous toxic nodules, surgery cures by removing all the overactive thyroid tissue; this allows the suppressed normal tissue to function again.

● Advantages. The goitre is removed, the cure is rapid and the cure rate is high if surgery has been adequate.

● Disadvantages. Recurrence of thyrotoxicosis occurs in at least 5% of cases when subtotal thyroidectomy is carried out. There is a risk of permanent hypoparathyroidism and nerve injury. Young women tend to have a poorer cos- metic result from the scar. Every operation carries a risk, but with suitable prepara- tion and an experienced surgeon the mortality is negligible and the morbidity low.

RADIOIODINE

Radioiodine destroys thyroid cells and, as in thyroidectomy, reduces the mass of functioning thyroid tissue to below a crit- ical level.

● Advantages. No surgery and no prolonged drug therapy.

● Disadvantages. Isotope facilities must be available. The patient must be quarantined while radiation levels are high and avoid pregnancy and close physical contact, par- ticularly with children. Eye signs may be aggravated. Choice of therapy Each case must be considered individually. Below are listed guiding principles on the most satisfactory treatment for a particular toxic goitre at a particular age; these must, how- ever, be modified according to the facilities available and the personality and wishes of the individual patient, business or family commitments and any other coexistent medical or sur- gical condition. Access to post-treatment care and availabil- ity of replacement thyroxine can be important considerations in resource-poor countries. In advising treatment, compliance, influenced by social and intellectual factors, is important; many patients cannot be trusted to take drugs regularly if they feel well, and indefi- nite follow-up, which is essential after radioiodine or subtotal thyroidectomy is a burden for all.

DIFFUSE TOXIC GOITRE

Most patients have an initial course of antithyroid drugs with radioiodine for relapse. Exceptions are those who refuse radi- ation, have large goitres, progressive eye signs or are pregnant.

TOXIC NODULAR GOITRE

Toxic nodular goitre is often large and uncomfortable and enlarges still further with antithyroid drugs. A large goitre should be treated surgically because it does not respond as well or as rapidly to radioiodine or antithyroid drugs as does a diffuse toxic goitre.

TOXIC NODULE

Surgery or radioiodine treatment is appropriate. Resection is easy, certain and with a low risk of morbidity. Radioiodine is a good alternative for patients over the age of 45 years because the suppressed thyroid tissue does not take up iodine and thus there is minimal risk of delayed thyroid insufficiency.

FAILURE OF PREVIOUS TREATMENT WITH ANTITHYROID DRUGS OR RADIOIODINE

In this case, surgery or thyroid ablation with 123 I is appropriate.