necessary to stimulate the pituitary, is diseased
There is a tumor, cyst or other abnormal structure between the hypothalamus and pituitary gland that prevents the pituitary from receiving its stimulus to secrete TSH.
Usually patients with TSH deficiency also have deficient secretion of growth hormone, and may have deficient secretion of the gonadotropins, called LH and FSH, which stimulate puberty and reproduction, and ACTH, which is necessary for cortisol and hydrocortisone secretion by the adrenal gland.
Often the only sign of hypothyroidism during childhood is an abnormal rate of linear growth. Actually the child may not be short compared to other children of the same age if he or she were above average in height before the disease occurred. Therefore, the most important feature of hypothyroidism is a decrease in the rate or velocity of growth in height. If the disease is recognized early and adequately treated, the child will grow at an accelerated rate until reaching the same growth percentile where the child measured prior to the onset of hypothyroidism. Hypothyroidism progresses very slowly and insidiously, making the diagnosis difficult for physicians. In the more advanced and long-standing the child may have other general symptoms of hypothyroidism, such as easy fatigability, mild weight gain in association with a reduction in appetite, constipation, an intolerance of cold weather, dry skin, and either delayed (usual) or early (rare) onset of sexual development at adolescence.
The treatment of hypothyroidism, regardless of the cause, is easy and inexpensive. One or two tablets of the major thyroid hormone, thyroxine (trade names in the US are Levothroid, Levoxyl and Synthroid) once a day provides normal thyroid function and growth. The dose, depending upon the child's age, ranges between 50 ug (0.05mg) and 200 ug (0.2mg) although some infants require slightly lower doses. The blood levels of T4 and TSH should be monitored annually to assure that the dose remains adequate as the child grows. In most instances the treatment must be continued for life since the diseases that cause hypothyroidism are permanent rather than transient.
Every child that has a decrease in the rate of growth in height during childhood and adolescence should have blood tests to measure T4, free T4 and TSH in order to determine if the growth problem is caused by hypothyroidism.
Contributing Medical Specialist
Thomas P. Foley, Jr., M.D.
Professor of Pediatrics, University of Pittsburgh Children's Hospital
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