Hypothyroidism in Adults

What is Hypothyroidism in Adults ?

In hypothyroidism in adults, metabolic processes slow down because of a deficiency of the thyroid hormones triiodothyronine (T3) or thyroxine (T4).

Hypothyroidism is classified as primary or secondary. Primary hypothyroidism stems from a disorder of the thyroid gland itself. Secondary hypothyroidism is caused by a failure to stimulate normal thyroid function or by a failure of target tissues to respond to normal blood levels of thyroid hormones. Either type may progress to myxedema, which is clinically much more severe and considered a medical emergency.

The disorder is most prevalent in women; in the United States, incidence is increasing Significantly in people ages 40 to 50.

Causes of Hypothyroidism in Adults

Hypothyroidism results from a variety of abnormalities that lead to insufficient synthesis of thyroid hormones. Common causes of hypothyroidism include thyroid gland surgery (thyroidectomy), irradiation therapy inflammation, chronic autoimmune thyroiditis (Hashimoto's disease), or inflammatory conditions, such as amyloidosis and sarcoidosis.

The disorder may also result from pituitary failure to produce thyroid-stimulating hormone (TSH), hypothalamic failure to produce thyrotropin-releasing hormone, inborn errors of thyroid hormone synthesis, inability to synthesize thyroid hormones because of iodine deficiency (usually dietary), or the use of antithyroid medications such as propylthiouracil.

Signs & Symptoms of Hypothyroidism in Adults

Signs and symptoms, including:

• Dry puffy skin, especially on the face.
• Hair loss, especially thinning of the outer 1/3 of the eyebrows.
• Slowed speech and a hoarse, breaking voice.
• Impaired memory
• A slow heart rate with ECG changes including low voltage Signals. Diminished cardiac output and decreased contractility.
• Choking sensation or difficulty swallowing.
• Shortness of breath with a shallow and slow respiratory pattern.
• Impaired ventilatory responses to hypercapnia and hypoxia.

Diagnostic tests

Hypothyroidism is confirmed when radioimmunoassay with radioactive iodine (¹³¹I) shows low serum levels of T3 and T4. Supportive laboratory findings include the following:

• Serum TSH levels are used to determine the primary or secondary nature of the disorder. An increased serum TSH level with hypothyroidism is due to thyroid insufficiency; a decreased TSH level is due to hypothalamic or pituitary insufficiency.
• Serum cholesterol, alkaline phosphatase, and triglycerides levels are elevated.
• Normocytic neurochronic anemia is present.
• In myexedema coma, laboratory tests also show low serum sodium levels, decreased pH, and increased Pco2, indicating respiratory acidosis.
• Radioisotope scanning of the thyroid tissue identifies ectopic thyroid tissue.
• Skull X-ray, computed tomography scanning, and magnetic resonance imaging help to locate pituitary or hypothalamic lesions that may be the underlying cause of hypothyroidism.

Assessment Tip-Screening of newborns and the elderly is a prevention measure to detect hypothyroidism. The elderly, especially women, often attribute Signs and symptoms of hypothyroidism to effects of aging, and the diagnosis is overlooked.

Treatment

In hypothyroidism, recommended treatment consists of gradual thyroid hormone replacement with the synthetic hormone levothyroxine (T4) and, occasionally, liothyronine (T3). Treatment begins slowly, particularly in elderly patients, to avoid adverse cardiovascular effects; the dosage increases every 2 to 3 weeks until the desired response is obtained.

Rapid treatment may be necessary for patients with myxedema coma and those about to undergo emergency surgery (because of sensitivity to centra1 nervous system depression). In these patients, both I. V. administration of levothyroxine and hydrocortisone therapy is warranted.

Cultural Tip-In the United States, soil in the Great Lakes area is iodine deficient and therefore food grown in it is also deficient. Use of iodized salt provides sufficient amounts. In underdeveloped areas, prophylactic iodine supplements have successfully decreased the incidence of iodine-deficient goiter.

Prevention Tips

There is no way to prevent hypothyroidism.