Hyperthyroidism is a condition caused by an overactive thyroid gland which produces an excess of thyroid hormones. The symptoms of hyperthyroidism or thyrotoxicosis are many and varied – an enlarged thyroid gland (goitre) and weight loss being some of them – and treatment may include medication, radioactive iodine therapy or surgery.
Hyperthyroidism is the opposite of hypothyroidism or an underactive thyroid.
Causes of Hyperthyroidism
The thyroid gland, situated in the front of the neck, is a part of the endocrine system. It controls metabolism of the body by producing two main hormones – triiodothyronine (T3) and thyroxine (T4). Production of T3 and T4 is usually controlled by the pituitary, which produces the thyroid stimulating hormone (TSH). An excess of T3 and T4, resulting in hyperthyroidism, can occur due to a number of causes.
- Graves’ disease is the most common cause of hyperthyroidism. It is an autoimmune disorder causing enlarged thyroid gland (goitre). It tends to run in families and is seen to be more common in young women, usually between the ages of 30 and 40.
- Toxic multinodular goitre (Plummer’s disease).
- Toxic adenoma is a toxic solitary nodule which autonomously secretes excess thyroid hormones.
- Abnormal secretion of TSH by pituitary tumours.
- Thyroiditis – Subacute (de Quervain’s) thyroiditis is an inflammation of the thyroid gland caused by a viral infection.
- Postpartum thyroiditis – hyperthyroidism occurring for the first time within 6 months of delivery.
- Iodine-induced hyperthyroidism – in the diet (extra-iodized salt in iodine prophylaxis programmes in iodine-deficient parts of the world), radiographic contrast medium or in medication (amiodarone).
- Thyroid cancer.
- Factitious hyperthyroidism – this is a rare condition which occurs when a person takes excessive amounts of a thyroid hormone preparation (thyroxine). There is usually a co-existing psychological or psychiatric problem. It is sometimes seen in patients who are desperate to lose weight
- Struma ovarii – thyroid tissue present in dermoid or ovarian teratomas (cancer).
- In molar pregnancy or choriocarcinoma.
Symptoms of Hyperthyroidism
The symptoms are often non-specific and usually come on so insidiously that in many cases hyperthyroidism is diagnosed quite late.
The common signs and symptoms may be :
- Weight loss in spite of increased appetite.
- Heat intolerance.
- Tremor – usually fine tremor.
- Frequent bowel movements which may sometimes seem like diarrhoea.
- Angina (chest pain).
- Emotional lability.
- Menstrual problems such as amenorrhoea (missed or no period) or oligomenorrhoea (decreased periods).
- Hair loss.
- Pruritus (itching).
- In addition to goitre, Graves’ disease may produce exopthalmos (protrusion of the eyeballs), lid lag (on looking down the eyelid lags behind), lid retraction. This can lead to corneal irritation and ulceration.
Thyrotoxic storm or hyperthyroid crisis can be a life-threatening complication of hyperthyroidism, needing immediate medical attention. It can be manifested as high fever, palpitation, agitation, convulsion and coma. Recent thyroid surgery or radioiodine, infection, injury or myocardial infarction (heart attack) can precipitate a thyroid storm.
Treatment of Hyperthyroidism
Treatment will depend upon the cause, age of the patient, severity of symptoms and associated medical conditions.
There are broadly 3 options :
- Radioactive iodine.
Hyperthyroidism in pregnancy and children needs special management.
Antithyroid drugs such as methimazole and propylthiouracil – these decrease production of thyroid hormones. Agranulocytosis (bone marrow depression) is a serious side effect of these drugs. Beta-blocker drugs such as propranolol may be used for rapid control of symptoms.
A single dose of radioactive iodine is given orally. Development of permanent hypothyroidism (needing thyroid hormone replacement) may be a major side effect of treatment. This form of treatment is not used in pregnant and breastfeeding women and in patients with Graves’ disease complicated with eye problems. Concerns regarding cancer, birth defects or infertility in women treated with radioactive iodine may be unfounded.
Subtotal thyroidectomy (partial removal of the thyroid gland) may be an option in some cases, such as in pregnant women or a large goitre. An antithyroid drug or a beta-blocker is usually prescribed prior to surgery to control hyperthyroidism and make surgery easier. Damage to the recurrent laryngeal nerve may be a complication of surgery, producing hoarseness of voice, or the patient might develop hypothyroidism and may need thyroid hormone supplements for life.