When your thyroid function is low, you may feel tired, weak, and depressed, and you may gain weight. Hypothyroidism is the term for too little production of thyroid hormone, while hyperthyroidism is the term for too much. Dr. Jesper Karmisholt and colleagues at Aahus University Hospital in Denmark provided a review of subclinical hypothyroidism, a mild form that is very common and sometimes temporary.
There are two standard blood tests for hypothyroidism: thyroid stimulating hormone (TSH) and thyroxine (T4). When thyroid function is too low, the TSH value is too high, because it is the body's signal to the thyroid to produce more metabolism regulating hormones, including T4. Karmisholt defined subclinical hypothyroidism as a condition with TSH above the normal range, but T4 in the normal range. Approximately 5 to 8 percent of patients with subclinical hypothyroidism progress per year to standard hypothyroidism, with both TSH and T4 out of range.
Patients with standard hypothyroidism are treated with replacement levothyroxine. Those with subclinical hypothyroidism may be monitored without treatment. “It has been, and still is, much debated whether the abnormality should be treated with levothyroxine (L-T4) or not,” Karmisholt reported.
Karmisholt recommended the following schedule for monitoring persistent subclinical hypothyroidism:
1. Evaluation of TSH, T4, and symptoms every 6 months for the first 2 years.
2. Evaluation every year after 2 years.
3. After 3 years, monitoring can be stopped for patients with no symptoms, goiter, or signs of autoimmune disease.
4. Monitoring should be restarted if the patient gets pregnant, develops hypothyroid symptoms, or presents for general health evaluation.
The National Institutes of Health's PubMed web site gives possible causes of hypothyroidism:
1. Autoimmune damage, also known as Hashimoto's thyroiditis.
2. Viral thyroiditis.
3. Sheehan syndrome, a condition that may occur in a woman who bleeds excessively during pregnancy or childbirth.
4. Congenital defects.
5. Treatment for hyperthyroidism, including radioactive iodine, surgery, and drugs.
6. Radiation treatment for neck cancers.
7. Drugs used to treat other conditions, including lithium (for bipolar disorder) and amiodarone (for heart ventricular arrhythmias).
Women have more hypothyroidism than men, and age greater than 50 years is also a risk factor. Karmisholt reported that the causes of subclinical hypothyroidism resemble the causes of standard hypothyroidism, with autoimmune thyroiditis as the most frequent.
References:
1. PubMed Health. Hypothyroidism. Web. August 28, 2011.
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001393/
2. Karmisholt J et al, “Variation in thyroid function in subclinical hypothyroidism: importance of clinical follow-up and therapy”, European Journal of Endocrinology 2011; 164: 317-23. http://www.ncbi.nlm.nih.gov/pubmed/21208994
Reviewed August 31, 2011
by Michele Blacksberg R.N.
Edited by Jody Smith