Sub-clinical Hypothyroidism...To Treat Or Not?

Medical Author: Ruchi Mathur, M.D.
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

In my office last week, I saw a woman who was referred to me by a colleague. The patient was in good health, 48 years old and had no prior medical history of significance except an uncomplicated pregnancy and gallbladder surgery years ago.

While she was under the care of my colleague, a generalist, she had a routine annual physical. As part of that physical, she had a thyroid panel (this includes a screen for thyroid stimulating hormone [TSH] and for the circulating thyroid hormones T3 and T4). As it turns out, all of her evaluation was completely normal except for her thyroid panel. Her blood work revealed a normal T4 and T3 level, but an increased TSH. She was referred to me for assessment.

Her case is an example of a common condition called "sub-clinical hypothyroidism." Basically, with this condition, the pituitary gland, which is in charge of regulating the thyroid gland, produces extra amounts of TSH to stimulate the thyroid to maintain a normal circulating level of thyroid hormones. While this patient is not hypothyroid (her thyroid hormone levels are normal), her pituitary is working hard at keeping her thyroid hormone levels within the normal range. In a significant number of patients, the TSH levels must climb in order to continue to stimulate the thyroid gland. Eventually, over the course of months to years, the thyroid gland no longer responds. At this point, "sub-clinical hypothyroidism" turns into overt hypothyroidism.