Primary Hypothyroidism

Name Synonyms Chronic thyroiditis, Hashimoto's thyroiditis, atrophic thyroiditis

General
description Deficiency of thyroid hormone production causing symptoms such as weakness, lethargy, sleepiness and fatigue, slow speech, slow thought, cold intolerance, menstrual irregularity, depression, and weight gain.


Is it common? prevalence is 0.8% Differentiating
features This diagnosis is suspected based on signs and symptoms. It is a "great mimicker" of other diseases and if there are unexplainable signs and symptoms such as these, a TSH level should be checked. A high TSH level and low serum T4 and free T4 are diagnostic. Other features Memory impairment, constipation, hoarseness, deafness, shortness of breath, muscle and joint aches, tingling, chest pain, dry, coarse, cold skin, eye swelling, thin hair, decreased reflexes, hypertension, and slow heart rate Cause Hashimoto's thyroiditis and idiopathic myxedema
Iatrogenic: iodine 131 therapy for hyperthyroidism and subtotal thyroidectomy
Drug-induced: Iodide deficiency or excess, lithium, amiodarone, anti-thyroid drugs
Congenital: Synthetic enzyme defects and thyroid dysgenesis or agenesis Unnecessary
studies Serum T3 is of no value Natural history
untreated If children are untreated, this results in cretinism (mental and motor retardation, growth retardation and delayed puberty.
Untreated adults may be mild or severe. Mild would just have the above symptoms for life. If severe, myxedema may occur resulting in above symptoms being severe in nature with additional findings of scaling of the skin, doughy feeling skin, yellow-orange appearance to skin, variable degrees of heart block, enlarged heart, and congestive heart failure, until a fatal coma ensues. Goals of
therapy (Rx) To bring free T4 (L-thyroxine) and TSH levels into normal range and improve symptoms. 1st choice therapy L-thyroxine Other therapies used Patients with myxedema with resulting adrenal insufficiency may require glucocorticoids. Treatments to
avoid This syndrome may be caused by amiodarone (Cordarone®, an anti arrhythmic drug), lithium, and excessive iodine. Reason for Rx
choices Improve symptoms and prevent CNS problems. References Cecil's Essentials of Medicine, W.B.Saunders Company, 1993. Other resources Thyroid Disease at Gland Central on the Web