Introduction
Hypothyroidism is the second most frequent endocrine problem for older people and mainly women. Many of the signs and symptoms of hypothyroidism in older persons and women are blunted in their presentation, or the presentation is atypical, or the presentation may be dismissed as a normal reaction to aging. Although laboratory tests are remarkably improved in reliability, they still can pose difficulties in reaching a firm diagnosis. According to statistical results, about 15 million Americans suffer from hypothyroidism (American Medical Women’s Association 2007). Hypothyroidism is more often among women than men because of histological and biological differences.
Prevalence
The prevalence of hypothyroidism varies depending on ethnicity, the iodine content of the diet, and the criteria used to define the diagnosis. In the United States prevalence of hypothyroidism, as determined by elevated thyroid-stimulating hormone (TSH), varies from 4.4% to 7.3% in healthy adults above 55 years of age. High TSH is more prevalent in Caucasians than African-Americans (8.8% vs. 5.8%), in women than men (5.95 % to 8.5% vs. 2.3% to 4.4%), and in subjects older than 75 years of age. In America, 1 out of 5 women 75 years + have Hashimoto’s thyroiditis which can cause hypothyroidism (Mead, 2004; American Medical Women’s Association 2007).
Causes
Hypothyroidism is a systemic disorder that results in the decreased secretion of thyroid hormones because of loss of functional cells and metabolic changes. Signs and symptoms of this disorder vary with the severity of the disease. These include lethargy, weakness, dry atrophic skin, poor memory, constipation, and intolerance to cold (Renner, 2003). The first subtle presentation of Hypothyroidism in elderly women may be mild psychic disturbances such as withdrawal, depression, and mild forms of dementia (Blount et al 2006). Other atypical signs and symptoms such as fecal impaction, elevations in plasma, cholesterol, or triglycerides, macrocytic anemia, and congestive heart failure may be clinical indications of Hypothyroidism in the older adult. The aged adult may also develop incontinence, decreased mobility, and falls.
There are a number of causes of hypothyroidism, but the most common is the idiopathic atrophy of the gland. This thyroid gland failure is found more frequently in patients above the age of 50 years and deserves special consideration. At present, idiopathic atrophy is poorly understood. Significant decline in triiodothyronine (T 3 ) occurs with age, which is thought to reflect the reduced conversion of T 4 to T 3 in extrathyroidal locations. Collective signs, such as a slowed basal metabolic rate, thinning of the hair, and dry skin are characteristic of hypothyroidism in the young but are normal manifestations in the aged who have no history of thyroid deficiencies (Brown, 2003; Scinicariello et al 2995). According to Renner (2003): “thyroid hormone receptors, in the absence of thyroid hormone, repress gene expression. In the presence of thyroid hormone, the receptors activate gene expression. When there are no receptors, the genes are expressed at an intermediate baseline level” (p. 25).
Some of the aged do develop hypothyroidism and should be evaluated. This is one instance in which it is difficult, on the surface, to establish the presence or absence of disease. Pregnancy is the main risk factor for women. During this period, iodine requirements are high, and thus may lead to iodine deficiency. Also, pregnancy causes significant changes in reproductive hormones which may lead to hypothyroidism (Mead, 2004). “Many women go undiagnosed for long periods of time so that they lack the energy they need to function well in everyday life during their child’s early years when the demands placed on them are greatest” (Mead 2004, p. 612). Another problem is that menopause and hypothyroidism have similar manifestations, and for this reason, hypothyroidism can be undiagnosed. Collective signs, such as a slowed basal metabolic rate, thinning of the hair, and dry skin are characteristic of hypothyroidism in the young but are normal manifestations in the aged who have no history of thyroid deficiencies. Following Brown (2003): “Extreme maternal hypothyroidism leads to neurological cretinism, which can include spastic diplegia (a form of cerebral palsy), deafness, and severe mental retardation” (p. 642). Some of the aged do develop hypothyroidism and should be evaluated. This is one instance in which it is difficult, on the surface, to establish the presence or absence of disease (Crump and Gibbs 2005).
Diagnosis
The best test for diagnosis of primary hypothyroidism is the serum TSH concentration. When serum thyroid hormone concentrations decrease below an individual’s threshold for thyroid hormone sufficiency, serum TSH concentration increases. Serum TSH levels will be elevated in subclinical and overt hypothyroidism. Free T 4 should be measured when the TSH level is high. If the free T 4 level is normal, TSH levels should be repeated in 4 to 6 weeks, since they may be transiently elevated during the recovery phase of nonthyroid illness. The American Thyroid Association (2007) recommends the measurement of both TSH and free T 4 as initial tests in women with suspected hypothyroidism. Also, they recommend a total T 4, free thyroxine index (T 4 I), or sensitive TSH as the best initial test in women with suspected hypothyroidism. Isolated elevated TSH levels should be repeated in 4 to 6 weeks. Many sick and even normal elderly women may have abnormal levels of TSH. Furthermore, nonspecific illnesses, drugs, and decreased food intake may depress triiodothyronine (T 3 ) both in young and old women. TSH may show minor elevation during recovery from an illness, and T 4 can be affected by multiple factors (The American Thyroid Association 2007).
Treatment
Thyroid hormone replacement therapy is the treatment of overt hypothyroidism. The goal should be a full physiologic replacement. The preferred agent is levothyroxine (Synthroid) because of its long half-life and its conversion to T 3. Brand-name products are preferred over generic ones because they vary less in bioavailability from batch to batch. Levothyroxine requirements decrease with age (The American Thyroid Association 2007). Levothyroxine therapy for hypothyroid elderly women with or without overt heart disease should start at 25 μg/day. The dose is increased in increments of 25 μg at 8-week intervals until the serum TSH level returns to normal. In a study of postmenopausal women, it was found that long-term levothyroxine therapy was associated with the decreased bone density of the spine and hip. If women have low TSH levels, doctors suggest supraphysiologic levothyroxine treatment. To protect women from bone loss, the dosage of levothyroxine should not suppress the TSH below normal even if T 4 levels are normal (Scinicariello et al 2005).
The signs and symptoms of hypothyroidism often develop insidiously for women. As many as 70% of elderly people hypothyroid patients show typical symptoms and signs of hypothyroidism. For this reason, clinicians need to be aware that many older women and family members may mistake the signs of hypothyroidism and consider that these are only signs of aging. Hypothyroidism is a cause of reversible dementia; and even subclinical hypothyroidism may be associated with cognitive dysfunction, mood disturbance, and diminished response to standard psychiatric treatments.
References
American Medical Women’s Association (2007). Web.
The American Thyroid Association (2007). Web.
Blount, B., Pirkle, J., Osterloh, D. et al. (2006). Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States. Environmental Health Perspectives 114 (18), 1265.
Brown, V. (2003). Disrupting a Delicate Balance: Environmental Effects on the Thyroid. Environmental Health Perspectives 111 (1), 642.
Crump, K.S., Gibbs, J.P. (2005). Benchmark Calculations for Perchlorate from Three Human Cohorts. Environmental Health Perspectives 113 (8), 1001.
Mead, N. (2004). Mother’s Thyroid, Baby’s Health. Environmental Health Perspectives 112 (11), 612.
Renner, R. (2003). New Thyroid Theory: How Maternal Hormone Affects Developing Brains. Environmental Health Perspectives 111 (1), 25.
Scinicariello, F., Murray, L., Wilbur, S., Fowler, B.A. (2005). Genetic Factors That Might Lead to Different Responses in Individuals Exposed to Perchlorate. Environmental Health Perspectives 113 (11), 1479.