Primary Hypothyroidism Primary hypothyroidism in adults results mainly from autoimmune thyroiditis, it is more common in women than in men, and occurs between the ages of 40 and 60 years. In these patients, clinical features of hypothyroidism may be accompanied by the typical goitre of Hashimoto’s thyroiditis. When present, the goitre is usually firm in consistency, generally moderate in size, and often lobulated; well- defined nodules are unusual. Both lobes are enlarged, but the gland may be asymmetrical. Adjacent structures, such as the trachea, oesophagus, and recurrent laryngeal nerves may be com pressed but this is a rare occurrence. Goitre develops gradually over many years. Rarely, the thyroid enlarges rapidly and may be accompanied by pain and tenderness. In other cases of hypothyroidism due to autoimmune thyroiditis the gland is atrophied. Infiltrative ophthalmopathy similar to that of Graves’ disease occurs in a small proportion of patients.

Other organ- specific autoimmune diseases such as insulin- de pendent diabetes mellitus, Addison’s disease, premature ovarian failure, hypoparathyroidism, myasthenia gravis, and coeliac disease may coexist. Patients with primary hypothyroidism may also complain of vitiligo and alopecia. Primary autoimmune hypothyroidism may be present as a component of either the type I or type II polyglandular autoimmune syndrome. The specific association of primary hypothyroidism and primary adrenal cortical insufficiency is known as Schmidt’s syndrome. The type I syndrome consists of at least two of the triad of Addison’s disease, hypoparathyroidism, and chronic mucocutaneous candidiasis; other autoimmune dis orders, such as alopecia, chronic autoimmune thyroiditis, and mal absorption syndrome, may also be present. Autoimmune thyroid disease is reported in 10– 12% of these patients. Type I polyglandular autoimmune syndrome generally presents in childhood, whereas the type II syndrome is more common and usually presents in adult life. Addison’s disease, Hashimoto’s thyroiditis, and type 1 diabetes are the most common endocrine deficiencies found in these patients, although gonadal failure, pernicious anaemia, and vitiligo are observed in a significant percentage.

Rarely a combination of primary and pituitary hypothyroidism with or without ACTH deficiency occurs, presumably also on an autoimmune basis. Thus, other glands may be affected with increased frequency in patients with autoimmune hypothyroidism.

Postablative Hypothyroidism

 A common cause of hypothyroidism in adults is the type following total thyroidectomy for thyroid carcinoma or near- total thyroidectomy for euthyroid or toxic multinodular goitre or Graves’ disease. Hypothyroidism following radioiodine treatment for Graves’ hyperthyroidism is also frequent, and is currently regarded as a common outcome of 131 I treatment rather than a complication.

Overt hypothyroidism in patients who have received 131 I is often preceded by subclinical hypothyroidism, which may become ap parent within 2– 4 months after 131 I therapy. The early onset of hypothyroidism may cause distinct symptoms in the previously thyrotoxic patient who received 131 I or surgery. These patients may develop muscle cramps, often in large muscle groups (trapezius, latissimus dorsi, or the proximal muscles of the extremities).

Central Hypothyroidism

 The clinical picture of central hypothyroidism varies depending on the severity of thyroid failure, the extent of the associated hormone deficiencies, the age of the patients, and the nature of the underlying lesion. Central hypothyroidism is due to TSH deficiency caused by either hypothalamic or pituitary disease. The differentiation of secondary from primary hypothyroidism is important for the institution of the proper therapy. The clinical features of central hypothyroidism are similar to those of primary hypothyroidism, although generally less pronounced. The skin is pale and cool, but not as coarse and dry as in primary hypothyroidism. Periorbital and peripheral oedema are uncommon in patients with central hypothyroidism. Loss of axillary, pubic, and facial hair and thinning of the lateral eyebrows are more pronounced. The tongue is not enlarged, and hoarseness of the voice is not prominent as in primary hypothyroidism. The heart tends to be small, and blood pressure is low. Atrophic breasts and amenorrhoea are found in women.

Body weight is more likely to be reduced than increased. Defects in growth hormone and gonadotropin secretion usually precede TSH insufficiency, and in most cases ACTH secretion is the last to be affected. Growth failure with delayed skeletal maturation results from growth hormone deficiency in children. Hypoglycaemia may occur. Gonadotropin insufficiency results in impotence, loss of libido, di minished beard growth, amenorrhoea, infertility, and atrophy of the breasts in women. ACTH deficiency leads to weakness, postural hypotension, and depigmentation of the areole and of other normally pigmented areas of the skin. Symptoms and signs that arise directly from the hypothalamic or pituitary lesion may precede, accompany, and even obscure manifestations of pituitary failure. The manifestations of a sellar mass include headache and symptoms secondary to compression of adjacent structures with visual field disturbances and ophthalmoplegia.

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