Rarely, an enlarged gland may be the result of cancer in the thyroid.
Treatment A symptomless goitre may gradually disappear or be so small as not to merit treatment. If the goitre is large or is causing the patient di?culty in swallowing or breathing, it may need surgical removal by partial or total thyroidectomy. If the patient is de?cient in iodine, ?sh and iodised salt should be included in the diet.
Hyperthyroidism is a common disorder affecting 2–5 per cent of all females at some time in their lives. The most common cause – around 75 per cent of cases – is thyrotoxicosis (see below). An ADENOMA (or multiple adenomas) or nodules in the thyroid also cause hyperthyroidism. There are several other rare causes, including in?ammation caused by a virus, autoimune reactions and cancer. The symptoms of hyperthyroidism affect many of the body’s systems as a consequence of the much-increased metabolic rate.
Thyrotoxicosis is a syndrome consisting of di?use goitre (enlarged thyroid gland), over-activity of the gland and EXOPHTHALMOS (protruding eyes). Patients lose weight and develop an increased appetite, heat intolerance and sweating. They are anxious, irritable, hyperactive, suffer from TACHYCARDIA, breathlessness and muscle weakness and are sometimes depressed. The hyperthyroidism is due to the production of ANTIBODIES to the TSH receptor (see THYROTROPHIN-STIMULATING HORMONE (TSH)) which stimulate the receptor with resultant production of excess thyroid hormones. The goitre is due to antibodies that stimulate the growth of the thyroid gland. The exoph-
thalmos is due to another immunoglobulin called the ophthalmopathic immunoglobulin, which is an antibody to a retro-orbital antigen on the surface of the retro-orbital EYE muscles. This provokes in?ammation in the retro-orbital tissues which is associated with the accumulation of water and mucopolysaccharide which ?lls the orbit and causes the eye to protrude forwards.
Although thyrotoxicosis may affect any age-group, the peak incidence is in the third decade. Females are affected ten times as often as males; the prevalence in females is one in 500. As with many other autoimmune diseases, there is an increased prevalence of autoimmune thyroid disease in the relatives of patients with thyrotoxicosis. Some of these patients may have hypothyroidism (see below) and others, thyrotoxicosis. Patients with thyrotoxicosis may present with a goitre or with the eye signs or, most commonly, with the symptoms of excess thyroid hormone production. Thyroid hormone controls the metabolic rate of the body so that the symptoms of hyperthyroidism are those of excess metabolism.
The diagnosis of thyrotoxicosis is con?rmed by the measurement of the circulating levels of the two thyroid hormones, thyroxine and TRIIODOTHYRONINE.
Treatment There are several e?ective treatments for thyrotoxicosis. ANTITHYROID DRUGS These drugs inhibit the iodination of tyrosine and hence the formation of the thyroid hormones. The most commonly used drugs are carbimazole and propylthiouricil: these will control the excess production of thyroid hormones in virtually all cases. Once the patient’s thyroid is functioning normally, the dose can be reduced to a maintenance level and is usually continued for two years. The disadvantage of antithyroid drugs is that after two years’ treatment nearly half the patients will relapse and will then require more de?nitive therapy. PARTIAL THYROIDECTOMY Removal of three-quarters of the thyroid gland is e?ective treatment of thyrotoxicosis. It is the treatment of choice in those patients with large goitres. The patient must however be treated with medication so that they are euthyroid (have a normally functioning thyroid) before surgery is undertaken, or thyroid crisis and cardiac arrhythmias may complicate the operation. RADIOACTIVE IODINE THERAPY This has been in use for many years, and is an e?ective means of controlling hyperthyroidism. One of the disadvantages of radioactive iodine is that the incidence of hypothyroidism is much greater than with other forms of treatment. However, the management of hypothyroidism is simple and requires thyroxine tablets and regular monitoring for hypothyroidism. There is no evidence of any increased incidence of cancer of the thyroid or LEUKAEMIA following radio-iodine therapy. It has been the pattern in Britain to reserve radio-iodine treatment to those over the age of 35, or those whose prognosis is unlikely to be more than 30 years as a result of cardiac or respiratory disease. Radioactive iodine treatment should not be given to a seriously thyrotoxic patient. BETA-ADRENOCEPTOR-BLOCKING DRUGS Usually PROPRANOLOL HYDROCHLORIDE: useful for symptomatic treatment during the ?rst 4–8 weeks until the longer-term drugs have reduced thyroid activity.
Hypothyroidism A condition resulting from underactivity of the thyroid gland. One form, in which the skin and subcutaneous tissues thicken and result in a coarse appearance, is called myxoedema. The thyroid gland secretes two hormones – thyroxine and triiodothyronine – and these hormones are responsible for the metabolic activity of the body. Hypothyroidism may result from developmental abnormalities of the gland, or from a de?ciency of the enzymes necessary for the synthesis of the hormones. It may be a feature of endemic goitre and retarded development, but the most common cause of hypothyroidism is the autoimmune destruction of the thyroid known as chronic thyroiditis. It may also occur as a result of radio-iodine treatment of thyroid overactivity (see above) and is occasionally secondary to pituitary disease in which inadequate TSH production occurs. It is a common disorder, occurring in 14 per 1,000 females and one per 1,000 males. Most patients present between the age of 30 and 60 years.
Symptoms As thyroid hormones are responsible for the metabolic rate of the body, hypothyroidism usually presents with a general sluggishness: this affects both physical and mental activities. The intellectual functions become slow, the speech deliberate and the formation of ideas and the answers to questions take longer than in healthy people. Physical energy is reduced and patients frequently complain of lethargy and generalised muscle aches and pains. Patients become intolerant of the cold and the skin becomes dry and swollen. The LARYNX also becomes swollen and gives rise to a hoarseness of the voice. Most patients gain weight and develop constipation. The skin becomes dry and yellow due to the presence of increased carotene. Hair becomes thinned and brittle and even baldness may develop. Swelling of the soft tissues may give rise to a CARPAL TUNNEL SYNDROME and middle-ear deafness. The diagnosis is con?rmed by measuring the levels of thyroid hormones in the blood, which are low, and of the pituitary TSH which is raised in primary hypothyroidism.
Treatment consists of the administration of thyroxine. Although tri-iodothyronine is the metabolically active hormone, thyroxine is converted to tri-iodothyronine by the tissues of the body. Treatment should be started cautiously and slowly increased to 0·2 mg daily – the equivalent of the maximum output of the thyroid gland. If too large a dose is given initially, palpitations and tachycardia are likely to result; in the elderly, heart failure may be precipitated.
Congenital hypothyroidism Babies may be born hypothyroid as a result of having little or no functioning thyroid-gland tissue. In the developed world the condition is diagnosed by screening, all newborn babies having a blood test to analyse TSH levels. Those found positive have a repeat test and, if the diagnosis is con?rmed, start on thyroid replacement therapy within a few weeks of birth. As a result most of the ill-effects of cretinism can be avoided and the children lead normal lives.
Thyroiditis In?ammation of the thyroid gland. The acute form is usually caused by a bacterial infection elsewhere in the body: treatment with antibiotics is needed. Occasionally a virus may be the infectious agent. Hashimoto’s thyroiditis is an autoimmune disorder causing hypothyroidism (reduced activity of the gland). Subacute thyroiditis is in?ammation of unknown cause in which the gland becomes painful and the patient suffers fever, weight loss and malaise. It sometimes lasts for several months but is usually self-limiting.
Thyrotoxic adenoma A variety of thyrotoxicosis (see hyperthyroidism above) in which one of the nodules of a multinodular goitre becomes autonomous and secretes excess thyroid hormone. The symptoms that result are similar to those of thyrotoxicosis, but there are minor di?erences.
Treatment The ?rst line of treatment is to render the patient euthyroid by treatment with antithyroid drugs. Then the nodule should be removed surgically or destroyed using radioactive iodine.
Thyrotoxicosis A disorder of the thyroid gland in which excessive amounts of thyroid hormones are secreted into the bloodstream. Resultant symptoms are tachycardia, tremor, anxiety, sweating, increased appetite, weight loss and dislike of heat. (See hyperthyroidism above.)... goitre
thyroid gland. (See THYROID GLAND, DISEASES OF.)... liothyronine acid
A genetic disorder may impair the thyroid’s ability to secrete hormones and goitre may result. Thyroid infection is uncommon and leads to thyroiditis. Viral infection can cause extreme pain and temporary hyperthyroidism. Hormonal changes during puberty or pregnancy may cause a degree of goitre temporarily. Hyperthyroidism due to excessive production of by the pituitary gland is rare but can occur as a result of a pituitary tumour.
Because iodine is necessary for the production of thyroid hormone, its deficiency may lead to goitre. Severe iodine deficiency in children may cause myxoedema. (See also thyroid cancer.)
thyroid hormones The 3 hormones produced by the thyroid gland are thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, and calcitonin, which helps to regulate calcium levels in the body.... thyroid gland, disorders of
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T3 see triiodothyronine.
T4 see thyroxine.... systolic pressure
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