Causes and Incidence
The cause of some hypothyroidism is unknown but is thought to be autoimmune in origin. Other hypothyroidism is caused by destruction of thyroid or pituitary tissue by underlying disease, surgery, or radiation treatment. Hypothyroidism is a common disorder that affects all age groups. Women between 30 and 60 years of age are most often affected. It also occurs in approximately 1 of every 4,500 live births. The incidence is rising in the elderly population.
When the supply of thyroid hormone is inadequate, a general depression of most cellular enzyme systems and oxidative processes results, reducing the metabolic activity of the cells. This in turn reduces oxygen consumption, decreases energy production, and lessens body heat. Tissues are infiltrated by mucopolysaccharides, carotene is deposited in epidermal layers, adrenergic stimulation is decreased, protein effusion collects in the pericardial and pleural sacs, and proteinaceous ground substances are deposited in tissues.
Signs and symptoms are often insidious in onset. They include fatigue and lethargy; mild weight gain; cold, pale, dry, rough hands and feet; reduced attention span with memory impairment, slowed speech, and loss of initiative; swelling in extremities and around the eyes, eyelids, and face; menstrual irregularities; muscle aches and weakness; joint aches and stiffness; clumsiness; hyperstiff reflexes; decreased pulse; decreased blood pressure; agitation; depression; and paranoia.
Myxedema coma is a life-threatening complication of hypothyroidism that requires immediate treatment. Other complications include ischemic heart disease, congestive failure, pleural and pericardial effusion, deafness, psychosis, and anemia.
Serum and serum-free triiodothyronine and thyroxine are decreased; serum thyroid-stimulating hormone is increased in primary hypothyroidism and decreased in secondary hypothyroidism.
Oral replacement thyroid hormone; IV form is used for myxedemic coma.
Lifelong monitoring; instruction about lifelong thyroid hormone replacement therapy and the importance of consistent and timely use.