Patterns of Hypothyroidism: Subclinical and Clinical
Hypothyroidism can be divided into two types: sub-clinical with mild symptoms and ‘normal’ or borderline normal lab tests and clinical or overt hypothyroidism, where symptoms are obvious and lab tests confirmatory. Combined evaluation of thyroid stimulating hormone (TSH) and free-thyroxine can detect overt hypothyroidism (high TSH with low free-thyroxine levels) and subclinical hypothyroidism (high TSH with normal free-thyroxine levels). With subclinical hypothyroidism in particular, many women present with normal labs. See Normal Labs with Symptoms of Hypothyroidism.
For more information about how the thyroid gland works see the Thyroid Gland: Where it is and What it Does.
Thyroid Function and the Aging Woman
Several changes in thyroid hormone concentrations occur with aging. The Whickham Survey undertaken in Britain provided data showing that thyroid stimulating hormone (TSH) levels did not vary with age among males, but increased markedly among females after the age of 45 years.
More recent data from the National Health and Nutrition Survey confirmed that both TSH levels and the presence of anti-thyroid antibodies are greater in women, increase with age, and are not only gender and age, but also race-related, being more common in whites than in blacks. The low serum concentrations of TSH result in clear, age-dependent declines in serum total and free-thyroxine levels, whereas the reduction of both total thyroxine secretion and peripheral T4 degradation of thyroxine results in no change in serum total and free thyroxine concentrations.
To Test or Not To Test
There is quite a bit of disagreement regarding whether or not to regularly test for thyroid dysfunction. The American Thyroid Association recommends screening both women and men at 35 years of age, and every 5 years thereafter. The American College of Pathologists recommends evaluations for women aged over 50 years with one or more general symptoms that could be caused by thyroid disease. In 2004, an independent panel sponsored by three major professional societies – the American Thyroid Association, the American Association of Clinical Endocrinologists, and the Endocrine Society – recommended such screening. In contrast, some organizations, e.g. US Preventive Services Task Force, decided to not recommend screening for adults or for the elderly. (It should be noted that there is similar controversy regarding whether or not to test pregnant women for thyroid dysfunction.)
Current Treatments for Hypothyroidism in the Elderly
Overt hypothyroidism. Typical treatment of overt hypothyroidism includes the use of Levothyroxine or L-thyroxine, for elderly patients. Research suggests that elderly individuals with high TSH levels commonly have a prolonged life span. Low serum free thyroxine levels are also associated with longer survival possibly due to adaptive mechanism that prevents excessive catabolism. Synthetic levothyroxine is frequently prescribed to be peripherally converted to free triiodothyronine, the active form of thyroid hormone. After stabilization, TSH levels can be monitored yearly. The most frequent complications of treatment in older people are myocardial ischemia and arrhythmias, especially atrial fibrillation, although these still occur at a low rate.
Subclinical hypothyroidism. Symptoms of subclinical hypothydroidsim may be treated to avoid progression to overt disease. There is no doubt about the indication for treatment of overt disease; however, the same is not true for subclinical disease. Some data indicate that treatment of subclinical disease results in lipid profile improvement, but there is no evidence that this improvement is associated with a decrease in cardiovascular or all-cause mortality in elderly patients. Indeed a recent study evaluating thyroid function in elderly patients found that higher TSH, which is associated with clinical and subclinical hypothyroidism was associated with lower mortality while higher free-thyroxine was associated with increased mortality. Moreover, none of the 599 patients (aged 85 years) who participated in the study, progressed from subclinical to overt hypothyroidism over the course of the three-year study.
Close monitoring of thyroid function could be the best option for patients at risk of hypothyroidism.