Before you begin reading about hypothyroidism, please read a description of the thyroid gland for a basic understanding of its structure and function.
Hypothyroidism (underactive thyroid) is a condition in which the thyroid gland does not make enough thyroid hormone. There are several types of hypothyroidism in children:
Congenital hypothyroidism (CH) occurs when the thyroid gland does not develop or function normally prior to birth. It is a very common problem, affecting about 1 in every 2,500 to 3,000 babies. In the United States, all states test for CH as part of their routine newborn screening programs.
Many factors, including your family history, the physical exam, the degree of hypothyroidism in your baby at the time of diagnosis, and the course of treatment over the first two to three years of life, will help your physician determine if the cause is hereditary (runs in your family), and if life-long therapy is required. In general, there is little benefit from pursuing extensive laboratory or radiologic testing, but these options can be discussed with your physician.
Acquired hypothyroidism includes autoimmune hypothyroidism and iatrogenic hypothyroidism.
Acquired hypothyroidism is most frequently caused by an autoimmune disorder called chronic lymphocytic thyroiditis (CLT). In this disorder your child’s immune system attacks the thyroid gland, leading to damage and decreased function. The disorder was originally described by a Japanese physician and thus is often referred to by his name: Hashimoto’s thyroiditis. CLT is more common in girls than in boys, and in adolescents than pre-adolescents. Patients with other forms of autoimmune disease, most commonly insulin-dependent diabetes, are at increased risk of developing CLT. Overall, about 20 to 30 percent of diabetics will develop CLT and, because of this, annual screening for CLT is a routine part of diabetic care. The opposite is much less common, but can occur: to have CLT and then subsequently develop insulin-dependent diabetes.
Diagnosis of CLT may include:
Iatrogenic hypothyroidism is a form of acquired hypothyroidism that occurs in people who have had their thyroid gland medically ablated (destroyed) or surgically removed. By removing the thyroid gland, the body no longer produces thyroid hormone, leading to iatrogenic hypothyroidism.
Severe hypothyroidism can lead to decreased metabolism and decreased use of calories. However, hypothyroidism is very rarely the cause of being overweight and obese. Despite this reality, medical providers often order thyroid function tests as part of the routine screening in overweight patients. This is a reasonable practice. Thyroid function testing should be ordered at the same time as testing for elevated cholesterol, as hypothyroidism is associated with elevated LDL levels (“bad” cholesterol) due to decreased metabolism or clearance of LDL and, subsequently, elevated total cholesterol.
Being overweight is associated with mild elevations in TSH that are not a reflection of thyroid disease, but an association with excess weight. In other words, it is more common for excess weight to lead to a mild increase in TSH rather than a mild increase in TSH to result in a significant increase in weight. In order to confirm the relationship between excess weight and a mild increase in TSH, your child's doctor should review the linear growth (gain in height) to determine if the increase in weight is accompanied by normal or increased height, as opposed to decreased linear growth, which is more frequently associated with hypothyroidism. He may also order laboratory testing for Hashimoto’s thyroiditis (described above) or elevated LDL and total cholesterol to determine whether the hypothyroidism should be treated.
Hypothyroidism is a common condition which can go undetected if symptoms are mild. Symptoms of hypothyroidism are usually very subtle and gradual, and may include:
The symptoms of hypothyroidism may resemble those of other conditions or medical problems. Always consult your physician for a diagnosis.
Screening for hypothyroidism involves a blood test, called thyroid function screening, that measures thyroid hormone (thyroxine or T4) and serum TSH (thyroid-stimulating hormone) levels. Hypothyroidism is diagnosed when the TSH levels are above normal and T4 levels are below normal. A less severe or earlier form of hypothyroidism is reflected by an elevated TSH and a low-normal T4, a condition called "compensated" or "subclinical" hypothyroidism.
In general, patients with hypothyroidism will be evaluated and cared for in the Division of Endocrinology and Diabetes and referred to the Pediatric Thyroid Center if needed.
Hypothyroidism is generally treated with thyroid hormone replacement pills in people of all ages, from newborn to adult. In newborns, parents or caregivers can crush the tablet and give with breast milk or formula via a teaspoon. Older children can swallow or chew the medicine. Food can decrease the absorption, but in general, it is more important to remember to take the pill at about the same time every day (morning or night) than to be overly concerned about taking it on an empty stomach. You should avoid taking the pill at the same time as iron or calcium.