Hypothyroidism in adults
Hypothyroidism in adults: Excerpt from Handbook of Diseases
Hypothyroidism, a state of low serum thyroid hormone, results from hypothalamic, pituitary, or thyroid insufficiency. The disorder can progress to life-threatening myxedema coma. Hypothyroidism is more prevalent in women than in men; in the United States, incidence is rising significantly in people ages 40 to 50.
Causes
Hypothyroidism results from inadequate production of thyroid hormone, usually because of dysfunction of the thyroid gland due to surgery (thyroidectomy), radiation therapy (particularly with 131I), inflammation, chronic autoimmune thyroiditis (Hashimoto’s disease) or, rarely, conditions such as amyloidosis and sarcoidosis. It 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 hormone because of iodine deficiency (usually dietary), or the use of antithyroid medications such as propylthiouracil.
In patients with hypothyroidism, infection, exposure to cold, and sedatives may precipitate myxedema coma.
Signs and symptoms
Typically, the early clinical features of hypothyroidism are vague and may include fatigue, forgetfulness, sensitivity to cold, unexplained weight gain, and constipation. As the disorder progresses, characteristic myxedematous signs and symptoms appear, such as decreasing mental stability; dry, flaky, inelastic skin; puffy face, hands, and feet; hoarseness; periorbital edema; upper eyelid droop; 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, and nystagmus. Reflexes show delayed relaxation time (especially in the Achilles tendon).
Progression to myxedema coma is usually gradual, but when stress aggravates severe or prolonged hypothyroidism, coma may develop abruptly. Clinical effects include progressive stupor, hypoventilation, hypoglycemia, hyponatremia, hypotension, and hypothermia.
Diagnosis
Radioimmunoassay confirms hypothyroidism with low triiodothyronine (T3) and thyroxine (T4) levels.
Supportive laboratory findings include:
❑ increased TSH level when hypothyroidism is due to thyroid insufficiency; decreased TSH level when hypothyroidism is due to hypothalamic or pituitary insufficiency
❑ elevated levels of serum cholesterol, alkaline phosphatase, and triglycerides
❑ normocytic, normochromic anemia.
In myxedema coma, laboratory tests may also show low serum sodium levels as well as decreased pH and increased partial pressure of carbon dioxide, indicating respiratory acidosis.
Treatment
Therapy for hypothyroidism consists of gradual thyroid hormone replacement with levothyroxine and, occasionally, liothyronine.
Clinical tip The TSH level is the most reliable marker to follow in primary hypothyroidism. It should be kept within the normal range.
During myxedema coma, effective treatment supports vital functions while restoring euthyroidism. To support blood pressure and pulse rate, treatment includes I.V. administration of levothyroxine and hydrocortisone to correct possible pituitary or adrenal insufficiency. Hypoventilation requires oxygenation and respiratory support.
Other supportive measures include fluid replacement and antibiotics for infection.
Special considerations
To manage the hypothyroid patient:
❑ Provide a high-bulk, low-calorie diet, and encourage activity to combat constipation and promote weight loss. Administer cathartics and stool softeners as needed.
❑ After thyroid replacement therapy begins, watch for symptoms of hyperthyroidism, such as restlessness, sweating, and excessive weight loss.
❑ Tell the patient to report signs of aggravated cardiovascular disease, such as chest pain and tachycardia.
❑ To prevent myxedema coma, tell the patient to continue his course of thyroid medication even if his symptoms subside.
❑ Warn the patient to report infection immediately and to make sure any physician who prescribes drugs for him knows about the underlying hypothyroidism.
Treatment of myxedema coma requires supportive care:
❑ Check frequently for signs of decreasing cardiac output (such as falling urine output).
❑ Monitor temperature until stable. Provide extra blankets and clothing and a warm room to compensate for hypothermia. Rapid rewarming may cause vasodilation and vascular collapse.
❑ Record intake and output and daily weight. As treatment begins, urine output should increase and body weight should decrease.
❑ Turn the edematous bedridden patient every 2 hours, and provide skin care, particularly around bony prominences, at least once a shift.
❑ Avoid sedation when possible or reduce the dose because hypothyroidism delays metabolism of many drugs.
❑ Maintain a patent I.V. line. Monitor serum electrolyte levels carefully when administering I.V. fluids.
❑ Monitor vital signs carefully when administering levothyroxine because rapid correction of hypothyroidism can cause adverse cardiac effects. Report chest pain or tachycardia immediately. Watch for hypertension and heart failure in the elderly patient.
❑ Check arterial blood gas values for indications of hypoxia and respiratory acidosis to determine whether the patient needs ventilatory assistance.
❑ Because myxedema coma may have been precipitated by an infection, check possible sources of infection, such as blood or urine, and obtain sputum cultures.
Book Source Details
- Book Title: Handbook of Diseases
- Author(s): Springhouse
- Year of Publication: 2003
- Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.
More About Hypothyroidism
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Medical Books Excerpts
- Hypothyroidism
- "The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter" (2000)
- [ read ]
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Handbook of Diseases
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2003
ISBN: 1-58255-266-5
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