Hypothyroidism – The Hidden Challenge
When thyroid function is normal, the actions of thyroid hormone are transparent to the clinical observer. When there is thyroid dysfunction, in which either excessive or insufficient amounts of thyroid hormone are produced, the effect can be dramatic and may be seen in diverse organ systems including the cardiovascular, central nervous and reproductive systems. So important are the actions of thyroid hormone that even when the thyroid function is mildly abnormal, the end-organ impact on overall health can be significant, even if the symptoms and science are imperceptible to the patient.
Unfortunately, thyroid dysfunction, particularly hypothyroidism, frequently is not suspected as the underlying reason for patient visits unless obvious symptoms and signs, such as goiter, fatigue, unexplained weight gain, menstrual irregularity and cold intolerance are found.
Patients and physicians often attribute complaints that may be a consequence of thyroid dysfunction to other causes. Patients with thyroid dysfunction may be seen numerous times by a physician before a serum TSH (thyroid stimulating hormone) level is measured and the correct diagnosis made.
Patients may be treated for other conditions while the underlying thyroid deficiency remains undiagnosed. The prolonged time before an accurate diagnosis is made not only may result in inappropriate utilization of health care resources in terms of both cost and physician time, but also can lead to protracted suffering for the patient.
More common than overt hypothyroidism but less frequently diagnosed is mild thyroid failure. Patients with mild thyroid failure, also called sub-clinical hypothyroidism, may have few or no clinical symptoms or signs recognized as arising from hormone deficiency. However, ever mild thyroid failure can be associated with such abnormalities as hypercholesterolemia and depression. A high index of suspicion is useful in recognizing this common problem, especially in high risk individuals such as women, particularly elderly women, and patients with family or personal history of thyroid dysfunction.
Within the last decade, the development of sensitive TSH assays has permitted accurate diagnosis of mild thyroid failure, even when symptoms and signs are absent. An elevated serum TSH level, even in the presence of a normal free thyroxine (FT4) value, strongly suggests mild thyroid failure. The assay is widely available. Thus compared with the potential clinical and economic costs of failing to diagnose thyroid failure correctly and to treat it appropriately, it may be cost effective to obtain TSH measurement in patients at risk.
Are certain patients at greater risk for developing thyroid failure?
Individuals at higher risk for hypothyroidism include:
- In a follow up to the landmark Whickham study, hypothyroidism was found to occur in 9.3% of women, compared with 1.3% of men.
- Individuals as they age
- Patients who have positive antithyroid antibodies
- Patients with a history of diabetes or other endocrinopathies.
- Persons with autoimmune disease.
- Patients taking certain medication, such as lithium carbonate and amiodarone.
- Patients who have hypercholesterolemia.
It is also important to note that a high percentage of patients with mild thyroid failure progress to overt hypothyroidism. With even minimal elevations in serum TSH values carry an increased risk of progressing to overt hypothyroidism, and higher the TSH value, higher the risk. If the TSH elevation is accompanied by positive antithyroid antibodies, the risk of progression becomes higher yet.
Is it cost–effective to screen for thyroid failure?
In the study published in JAMA 1996, the investigators compared the cost–effectiveness of screening the general population for thyroid dysfunction with that of other screening strategies, such as for hypertension, hypercholesterolemia, and even breast cancer and found the cost effectiveness of TSH screening to be comparable or perhaps less. Additional research on the cost-effectiveness of screening thyroid dysfunction and the factors most likely to affect cost-effectiveness would be helpful.
Why should patients with mild thyroid failure be treated?
To avert the progression of mild thyroid failure to overt hypothyroidism.
To reduce elevated cholesterol levels, thereby reducing cardiovascular risk.
To reverse the effects of mild thyroid deficiency on many organ systems and relieve subtle symptoms and signs caused by thyroid hormone deficiency, thus improving patients quality of life.
These symptoms may drive patients to seek repeated physician visits vague complaints not easily recognizable as related thyroid failure.
As Cooper and colleagues have shown, patients with mild thyroid hormone replacement experience relief from a host of symptoms, while the symptoms of untreated patients worsen.
The multidisciplinary panel concluded that overt hypothyroidism and mild thyroid failure are common, reversible medical problems that, left untreated, are associated with significant long term health consequences that can affect many organ systems. The system of over hypothyroidism and mild thyroid failure often mimic those of other common disorders such as depression, and an incorrect diagnosis may lead to inappropriate treatment. A definitive diagnosis may be made using a TSH assay. Screening for thyroid hormone deficiency using the TSH assay is cost-effective compared with other common interventions, such as for hypertension, hyperlipidemias, and breast cancer. Thyroid failure can be easily treated with thyroid hormone replacement therapy (L-thyroxine). Treatment can reverse the signs and symptoms of mild thyroid failure and can often result in the normalization of lipids. Treatment can prevent progression to more serious thyroid disease.
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- Danese MD, Powe NR, Sawin CY, Ladenson PW. Screening of mild thyroid failure at the periodic health examination: a decision and cost effective analysis. JAMA. 1996;276:285-292.
- Cooper DS, HalpermR, WoodLC, LevinAA, Ridgway EC. L thyroxine therapy in sub-clinical hypothyroidism: a double blind, placebo controlled trial. Ann Intern Med. 1984:101:18-24.