Hypothyroidism Overt hypothyroidism occurs in 2% of women, and at least an additional 5% develop sub-clinical hypothyroidism. This is another disease that disproportionally impacts women five-to eightfold more commonly than men. This is especially true in the elderly, in whom many of the signs and symptoms are subtle. The principal cause of hypothyroidism is autoimmune thyroiditis (Hashimoto’s thyroiditis). A familial predisposition is observed in many cases, but the specific genetic or environmental trigger is unknown. The incidence of autoimmune thyroiditis increases with age, affecting up to 15% of women older than 65 years. Many have subclinical hypothyroidism, which is defined as an elevated serum TSH concentration with a normal serum free T4 level. It is uncertain whether treatment will improve quality of life in otherwise healthy patients who have subclinical hypothyroidism (41,42). Chronic autoimmune thyroiditis (Hashimoto’s) is the more common cause of hypothyroidism in countries without iodine deficiency. In this process one has both cellular and antibody-mediated destruction of the thyroid, which can result in either a goiter or atrophic thyroid. Autoimmune thyroiditis may be associated with other endocrine (e.g., type 1 diabetes, primary ovarian failure, adrenal insufficiency, and hypoparathyroidism) and nonendocrine (e.g., vitiligo and pernicious anemia) disorders (43). When autoimmune diseases are present, there should be a high degree of suspicion for concurrent thyroid disorders. With postpartum thyroiditis there will be a hyperthyroid phase followed by a hypothyroid phase that can last for months. Iatrogenic causes of hypothyroidism occur after surgical removal or radioactive iodine therapy for hyperthyroidism (Graves) or thyroid cancer. Radiation was used to treat acne and other dermatologic disorders 45 years ago; patients undergoing such treatment have an increased risk of thyroid cancer and require close monitoring. Although worldwide iodine deficiency goiter is the most common form of hypothyroidism, this is uncommon in North America given the iodine supplementation in salt as well as other dietary sources. Hypothyroidism rarely occurs secondary to pituitary or hypothalamic diseases from TSH or TRH deficiency, but this must be considered if symptoms occur after neurosurgical procedures.
Clinical Features Manifestations of hypothyroidism include a broad range of signs and symptoms: fatigue, lethargy, cold intolerance, nightmares, dry skin, hair loss, constipation, periorbital carotene deposition (causing a yellow discoloration), carpal tunnel syndrome, weight gain (usually less than 5–10 kg), depression, irritability, hyperlipidemia, and impaired memory. Menstrual dysfunction is common, either as menorrhagia or amenorrhea. Infertility may arise from anovulation, but exogenous thyroid hormone is not useful for anovulatory euthyroid women. The finding of hyperlipidemia may be the first indication of hypothyroidism, especially the presence of high triglycerides. Empirical use of thyroid extract should be discouraged.
Hypothyroidism is not a cause of premenstrual syndrome (PMS), but worsening PMS may be a subtle manifestation of hypothyroidism (44). Hypothyroidism may cause precocious or delayed puberty. Hyperprolactinemia and galactorrhea are unusual manifestations of hypothyroidism; however, assessment of thyroid function should be considered. To distinguish primary hypothyroidism from a prolactin-secreting pituitary adenoma, TSH levels should be assessed in women who have amenorrhea, galactorrhea, and hyperprolactinemia.