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Impairment in Driving May Be a Consequence of Hypothyroidism

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What is Hypothyroidism?

Hypothyroidism is a medical condition which is caused by a deficiency of the thyroid hormone. It is marked by clinical characteristics such as its typical facies, hoarse slow speech, and dry skin and by low levels of thyroid hormones. This condition can occur at any age yet it is more common among the elderly. It is more common among women who are aged 65 and above.


Hypothyroidism may either be primary or secondary. Primary hypothyroidism is caused by disease in the thyroid while secondary hypothyroidism is caused by diseases in the hypothalamus or pituitary. Primary hypothyroidism may be due to diseases that originate from thyroid gland. In these conditions, the thyroid-stimulating hormone (TSH) is increased. Primary hypothyroidism is commonly autoimmune such as in the case of Hashimoto thyroiditis; it may also be associated with a firm goiter or a shrunken fibrotic thyroid with little or no function. The second most common cause it post-therapeutic hypothyroidism, especially after radioactive iodine therapy or surgery for hyperthyroidism or goiter. Primary hypothyroidism may also be due to overtreatment with propylthiouracil, methimazole, and iodide; the hormone levels go normal when treatment is stopped. Iodine deficiency may also cause congenital hypothyroidism which is a major cause of intellectual disability. Primary hypothyroidism may also be due to rare inherited enzymatic defects which can alter the synthesis of thyroid hormone and cause goitrous hypothyroidism. Another cause is lithium intake lithium inhibits hormone release by the thyroid; amiodarone or other iodine-containing drugs and interferon-alfa may also cause primary hypothyroidism.

Secondary hypothyroidism, on the other hand, occurs when the hypothalamus produces insufficient thyrotropin-releasing hormone (TRH) or the pituitary produces insufficient TSH.

Hypothyroidism can bring about insidious signs and symptoms such as include cold intolerance, constipation, forgetfulness, and personality changes. There may also be modest weight gain which may be due to fluid retention and decreased metabolism. There may also be numbness and tingling of the hands and the feet which may be due to to carpal-tarsal tunnel syndrome caused by deposition of proteinaceous ground substance in the ligaments around the wrist and ankle. Women with hypothyroidism may experience menstrual problems.

The face may appear with a dull expression while the voice may be hoarse and the speech may be slow. There may also be puffiness of the face and swelling of the area around the eyes due to infiltration with the mucopolysaccharides hyaluronic acid and chondroitin sulphate. The eyelids may appear drooping because of decreased adrenergic drive while the hair may become coarse and dry and sparse. The skin is often scaly, coarse, dry and thick. There may be slowing of tendon reflexes, hypothermia, dementia and even psychosis.

 Impairment in Driving May Be a Consequence of Hypothyroidism

A recent study shows that those who have significant hypothyroidism can experience impaired driving similar to those who are driving when intoxicated by alcohol. This study, done by researchers from Kentucky and the Veterans Affairs Medical Center in Lexington, KY, found that hypothyroid patients being tested on a driving simulator had a similar performance to that of drivers with a blood alcohol level above the legal limit in the U.S. The researchers studied thirty-two patients with thyroid cancer, who were undergoing preparation for radioactive iodine scanning by stopping thyroid hormone. These patients were evaluated with neurological and psychological tests, as well as testing on a driving simulator. They were studied when they were taking thyroid hormone, again when they were off of thyroid hormone, and then finally when they were back on thyroid hormone therapy. Hypothyroid patients had depression and also showed declines in neurological function that resulted in increased automobile braking times.

More medical breakthroughs are discussed in our other articles on this site.