Hypothyroidism is a condition characterized by low levels of thyroid hormones. The underproduction of thyroid hormones can result from an abnormality either in the thyroid gland itself, the pituitary gland, or the hypothalamus. Congenital hypothyroidism is not common. This paper will discuss the etiology, pathophysiology, signs and symptoms, treatment, and preventive measures of hypothyroidism.
Hypothyroidism caused by thyroid abnormalities is known as primary hypothyroidism. Primary hypothyroidism can be caused either by autoimmune destruction of the thyroid gland (Hashimoto thyroiditis) or iodine deficiency. Hashimoto thyroiditis is an autoimmune disease in which anti-thyroid peroxidase and anti-thyroglobulin antibodies are produced. Iodine deficiency is the commonest cause of hypothyroid states in the world. It is common in geographical areas with little or no iodine in the soil. Secondary hypothyroidism is caused by insufficient stimulation of the thyroid gland by the pituitary gland (insufficient TSH production). Tertiary hypothyroidism is caused by inadequate stimulation of the pituitary gland by the hypothalamus (insufficient production of TRH). Thyroidectomy and radioactivity can also cause the condition.
Thyroid hormones (thyroxine (T4) and triiodothyronine (T3)) have several effects on different organs and body systems. T3 is more active than T4. T3 modifies many metabolic functions in the body. The metabolic effects of T3 include stimulation of oxygen consumption in most metabolically active tissues, enhanced absorption of carbohydrates, and regulation of lipid metabolism. In hypothyroid states, these functions are either diminished or absent. Several body systems cease to function properly. The most affected systems are the nervous system, cardiovascular system, musculoskeletal system, and respiratory system. Signs and symptoms of hypothyroidism are a reflection of these derangements.
Signs and symptoms of the condition include malaise, weight gain (fluid retention), dry hair, dry skin, alopecia, cold intolerance, muscle cramps and aches, abdominal problems like constipation, cognitive problems like memory loss and poor concentration, diminished libido, depression, thyroid hypertrophy (goiter), and irritability. The most serious effects of thyroid hormone deficiency are myxedema coma and cretinism. Cretinism causes mental retardation in children.
Diagnosis of hypothyroidism relies heavily on clinical findings. A comprehensive history, physical examination findings, and other subjective information may be used to make a clinical diagnosis. A definitive diagnosis is made in the laboratory using serum assays of TSH. In hypothyroidism, serum TSH levels are markedly elevated.
Thyroid hormone replacement is the most preferred mode of treatment (Hueston, 2001). In hormone replacement therapy, synthetic T4 is administered. T3 and combined T3 and T4 have also been tested. T4 is available in a preparation called levothyroxine. The adult dose is 1.5 micrograms per kilogram. However, higher doses are recommended when treating infants and children. Immunosuppressants may be used to manage Hashimoto thyroiditis. Serious adverse events have been reported in elderly patients (Griffin, 1990; Turner et al., 2011).
Non-pharmacological management of the condition revolves around iodine intake. Patients suffering from iodine deficiency hypothyroidism can be managed using iodine supplementation. Fortification of food is an effective way of increasing intake. Table salt usually contains iodine. In some cases, thyroidectomy may be performed by a surgeon.
Control measures include increasing dietary intake of iodine and introduction of iodine into deficient soil. Incorporation of iodine into soil ensures that crops contain enough iodine. Salt is the only food additive fortified with iodine.
Hypothyroidism is a state characterized by low levels of T3 and T4. It is caused by abnormalities of thyroid hormone metabolism. The abnormalities could either be situated in the thyroid gland, the pituitary gland, or the hypothalamus. Primary hypothyroidism is caused by iodine deficiency. Hormone replacement therapy is the preferred mode of treatment.
References
Griffin, J. (1990). Hypothyroidism in the elderly. Am J Med Sci., 299,334-345.
Hueston, W. (2001). Treatment of Hypothyroidism. Am Fam Physician, 64(10), 1717-25.
Turner et al. (2011). Levothyroxine dose and risk of fractures in older adults: nested case-control study. BMJ, 342(d2238).