Hypothyroidism, a state of low serum thyroid hormone, results from hypothalamic, pituitary, or thyroid insufficiency.
The disorder can progress to life-threatening myxoedema coma. It results from scanty production of thyroid hormone typically because of dysfunction of the thyroid gland due to surgery, irradiation therapy, inflammation, or chronic autoimmune thyroiditis. It may also result from pituitary failure to yield thyroid-stimulating hormone (TSH), hypothalamic failure to yield thyrotropin-releasing hormone, inborn errors of thyroid hormone synthesis, and the incapacity to synthesise thyroid hormone because of iodine deficiency or the use of antithyroid medication. The initial clinical features of hypothyroidism are unclear:
- menstrual changes
- fatigue
- forgetfulness
- hypercholesterolemia
- unexplained weight gain
- sensitivity to cold
- constipation
As the disorder progresses, characteristic myxedematous signs and symptoms appear: dry, flaky, inelastic skin, decreasing mental stability, puffy face, hands, and feet, hoarseness, upper eyelid droop, periorbital oedema, dry, sparse hair, and thick, brittle nails. Cardiovascular involvement leads to decreased cardiac output, slow pulse rate, signs of poor peripheral circulation and, occasionally, an enlarged heart.
Other common effects include;
- anorexia
- abdominal distention
- menorrhagia
- decreased libido
- infertility
- ataxia
- intention tremor
- nystagmus
Reflexes show delayed relaxation time, especially in the Achilles tendon. Radioimmunoassay confirms hypothyroidism with low triodothyronine (T3) and thyroxin (T4) levels. Supportive laboratory findings include increased TSH levels when hypothyroidism is due to thyroid insufficiency, decreased TSH level when hypothyroidism is due to hypothalamic or pituitary insufficiency.
Bibliography
- Barnes, Broda O., and Lawrence Galton.Hypothyroidism: the unsuspected illness. New York: Crowell, 1976.
- Pratt, Maureen. Hypothyroidism: an essential guide for the newly diagnosed. New York, N.Y.: Marlowe and Co., 2003.
- Professional guide to diseases. 9th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2009.
