In medicine, hypothyroidism is "a syndrome that results from abnormally low secretion of thyroid hormones from the thyroid gland, leading to a decrease in basal metabolic rate. In its most severe form, there is accumulation of mucopolysaccharides in the skin and edema, known as myxedema."
Thyroid stimulating hormone levels of less than 10 may not be important.
Because the manifestations of hypothyroidism in the typical patient do no present the physician with a specific set of signs and symptoms, diagnosis of the disease usually requires laboratory tests.
If the initiating pathological process greatly affects the thyroid gland as its primary target, the thyroid hormone, thyroxin (T4), will show abnormally low concentrations in blood, while the pituitary hormone, thyrotropin (TSH), which normally stimulates the thyroid gland to secrete thyroid hormones, shows abnormally high concentrations in the blood, due to lack of the normal physiological feedback inhibition of TSH secretion by T4. In a sense, the pituitary gland, through excess TSH secretion 'tries' to compensate for the the low blood T4 concentrations by excess stimulation of the diseased thyroid gland.
If the elevated TSH concentration can maintain a normal or near normal T4 concentration, the diagnosis is subclinical hypothyroidism.
in some cases of hypothyroidism, referred to as central hypothyroidism, the hypothalamus, which normally produces a hormone, thyrotropin-releasing hormone (TRH), that stimulates the pituitary gland to secrete TSH, is abnormal, in which case the laboratory results will show and abnormally low T4 concentration in the blood without an appropriate compensatory increase in TSH concentration. In other cases of so-called central hypothyroidism, the primary problem may reside in the pituitary gland itself, also giving on laboratory testing a low T4 concentration and an inappropriately high TSH concentration.
Canaris and colleagues studied more than 25,000 participants of a state health fair in Colorado, and reported the following:
Results: The prevalence of elevated TSH levels (normal range, 0.3-5.1 mIU/L) in this population was 9.5%, and the prevalence of decreased TSH levels was 2.2%. Forty percent of patients taking thyroid medications had abnormal TSH levels. Lipid levels increased in a graded fashion as thyroid function declined. Also, the mean total cholesterol and low-density lipoprotein cholesterol levels of subjects with TSH values between 5.1 and 10 mIU/L were significantly greater than the corresponding mean lipid levels in euthyroid subjects. Symptoms were reported more often in hypothyroid vs euthyroid individuals, but individual symptom sensitivities were low.
Conclusions: The prevalence of abnormal biochemical thyroid function reported here is substantial and confirms previous reports in smaller populations. Among patients taking thyroid medication, only 60% were within the normal range of TSH. Modest elevations of TSH corresponded to changes in lipid levels that may affect cardiovascular health. Individual symptoms were not very sensitive, but patients who report multiple thyroid symptoms warrant serum thyroid testing. These results confirm that thyroid dysfunction is common, may often go undetected, and may be associated with adverse health outcomes that can be avoided by serum TSH measurement.
Causes of primary hypothyroidism
Taking replacement hormone at night may be better.
- Anonymous (2015), Hypothyroidism (English). Medical Subject Headings. U.S. National Library of Medicine.
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