Hypothyroidism
Thyroid deficiency affects all body functions and ranges from mild, subclinical disease to advanced forms. It results from suboptimal thyroid hormone levels and commonly follows prior treatment with radioiodine, antithyroid medications, or thyroidectomy. Myxedema is the accumulation of mucopolysaccharides in subcutaneous and other interstitial tissues.
Classification
Hypothyroidism is classified by cause. Central hypothyroidism is failure of the pituitary, the hypothalamus, or both to stimulate thyroid hormone production. Secondary (pituitary) hypothyroidism is caused entirely by a pituitary disorder. Tertiary (hypothalamic) hypothyroidism stems from a hypothalamic disorder that drops TSH through reduced TRH stimulation. In cretinism the thyroid disorder is present at birth.
Statistics and Epidemiology
Hypothyroidism occurs most often in older women. Thyroid cancer incidence is increased in men who underwent radiation therapy for head and neck cancer. More than 95% of patients with hypothyroidism have primary, or thyroidal, hypothyroidism.
Causes
The most common cause is inflammation that damages the gland's cells. In adults the leading cause is autoimmune thyroiditis (Hashimoto's disease), in which the immune system attacks the thyroid. The gland also atrophies and shrinks with aging. Treatments for hyperthyroidism, including radioactive iodine and thyroidectomy, can produce it, as can lithium, iodine compounds, and antithyroid medications that reduce TSH production. Both iodine deficiency and excess affect the gland. Some women develop hypothyroidism after pregnancy (postpartum thyroiditis).
Clinical Manifestations
Extreme fatigue makes a full day's work or usual activity difficult. Menstrual disturbances such as menorrhagia or amenorrhea occur. The patient gains weight without eating more and feels cold even in a warm room. Skin thickens from mucopolysaccharide accumulation in the subcutaneous tissue.
Prevention
Adequate iodine intake is the foremost prevention strategy. Thyroid testing after thyroid surgery or therapy allows early detection and prompt treatment.
Complications
Myxedema coma is the decompensated state of severe hypothyroidism in which the patient is hypothermic and unconscious. It is life-threatening.
Assessment and Diagnostic Findings
Inspect and palpate the thyroid routinely. Serum TSH is the single best screening test because of its high sensitivity, the position taken by the AACE and American Thyroid Association guidelines. Total T3 and T4 measure protein-bound and free hormone produced in response to TSH. Antithyroid antibody testing by immunoassay is positive in Hashimoto's thyroiditis (100%).
Medical Management
The objective is to restore a normal metabolic state by replacing the missing hormone. Synthetic levothyroxine is the preferred preparation for treating hypothyroidism and suppressing nontoxic goiters. Because subnormal metabolism means tissues need little oxygen, reduced blood supply is tolerated without overt coronary symptoms, so restore hormone carefully to protect the heart. Supportive care: monitor oxygen saturation, give fluids cautiously, avoid applying external heat, and continue oral thyroid hormone therapy.
Nursing Management
Nursing Assessment
Assess the thyroid from an anterior or posterior position. Auscultate the lobes with the diaphragm if abnormalities are palpated, and assess for firmness (Hashimoto's) or tenderness (thyroiditis).
Diagnosis
Common diagnoses include activity intolerance related to fatigue and depressed cognition, risk for imbalanced body temperature related to cold intolerance, constipation related to depressed GI function, ineffective breathing pattern related to depressed ventilation, and disturbed thought processes related to depressed metabolism and altered cardiovascular and respiratory status.
Planning & Goals
Goals: increased activity and independence, normal body temperature, return of normal bowel function, improved respiratory status and breathing pattern, and improved thought processes.
Nursing Interventions
Space activities to balance rest and tolerated exercise. Protect against cold with an extra layer of clothing or a blanket, and avoid external heat sources. Monitor body temperature. Encourage increased fluid intake within any fluid restriction and provide high-fiber foods. Monitor respiratory depth, rate, pattern, pulse oximetry, and ABG, and encourage deep breathing, coughing, and incentive spirometry. Orient the patient to time, place, date, and surrounding events.
Evaluation
Expected outcomes: increased participation and independence, maintained normal body temperature, return of normal bowel function, improved respiratory status and breathing pattern, and improved thought processes.
Discharge and Home Care Guidelines
Teach that medication compliance is lifelong. Have the patient avoid extreme cold until stable, keep regular followup visits, and use strategies for weight reduction and constipation prevention such as high-fiber, low-calorie intake and adequate fluids.
Documentation Guidelines
Document activity level; vital signs before, during, and after activity; core temperature initially and as needed; lab and diagnostic results; usual and current bowel pattern with duration and contributing factors; stool characteristics; respiratory pattern, breath sounds, and accessory muscle use; the plan and teaching plan; response to interventions; progress toward outcomes; modifications to the plan; and long-term needs.
Frequently Asked Questions
What is the most common cause of hypothyroidism? In adults the leading cause is Hashimoto's disease, an autoimmune thyroiditis in which the immune system attacks the thyroid, per NIDDK. Prior treatment for hyperthyroidism, such as radioactive iodine or thyroidectomy, is another common cause.
Which lab test best screens for hypothyroidism? Serum TSH is the single most sensitive screening test and the one the AACE and American Thyroid Association recommend for the vast majority of patients. T3 and T4 and antithyroid antibody testing add detail when needed.
How is hypothyroidism treated? Synthetic levothyroxine replaces the missing hormone and is the preferred preparation. Restore the hormone carefully in patients with cardiac risk, since raising metabolism too fast increases the heart's oxygen demand.
Is treatment lifelong? For most patients, yes. Teach that levothyroxine adherence is lifelong and that regular followup visits keep the dose correct.
What is myxedema coma? It is the decompensated state of severe hypothyroidism, with hypothermia and altered consciousness. It is life-threatening and the emergency never to miss.
Why do hypothyroid patients feel cold and gain weight? Low thyroid hormone slows metabolism across every system, which reduces heat production and energy use, so patients feel cold, fatigue easily, and gain weight without eating more.