Resistance syndromes
Resistance( insensitivity) syndromes to thyroid hormones are quite rare, transmitted by an autosomal dominant type of inheritance. Normally, with an increase in the number of thyroid hormones in the human blood, the formation of thyroid-stimulating hormone of the pituitary gland( the gland of the brain) decreases. This hormone, acting on the thyroid gland, causes an increase in the formation of its hormones. Thus, in principle, the principle of feedback: the increase in one decreases the amount of another hormone and vice versa. Due to this principle, the level of hormones in the human blood serum is maintained at approximately constant level. When syndromes of resistance to thyroid hormones, a paradoxical combination of high levels of thyroid hormones with an inadequately elevated level of thyroid-stimulating hormone is determined, that is, a violation of the feedback principle occurs. In addition, with these syndromes there are no typical symptoms of thyrotoxicosis. The development of syndromes of thyroid resistance is a violation of the sensitivity of various tissues to the hormones of the thyroid gland. By the end of the 1990s.a little more than 200 different variants of these syndromes are described in the world.
General( generalized) insensitivity to thyroid hormones includes central and peripheral resistance. Central resistance is that when the level of free hormones of the thymus gland does not adequately reduce the level of thyroid-stimulating hormone of the pituitary( TSH), its serum concentration in the blood serum remains within the normal range or may be slightly increased. Peripheral resistance is a violation of the sensitivity of peripheral tissues of the body to the action of thyroid hormones.
At present, most of the cases detected refer to the generalized form of the disease. Those people who have not received any treatment often determine the normal state of metabolism, which arises from the high level of circulating free thyroid hormones in the blood. Stability of the pituitary gland to thyroid hormones is the less common variant of the syndrome. He has elevated levels of free thyroid hormones( thyroxine and triiodothyronine), as well as normal( with respect to this case inadequately high) thyroid-stimulating hormone level. This syndrome is manifested by all signs of thyrotoxicosis( see above).Thus, for pituitary thyroid resistance, in contrast to generalized, the symptoms of thyrotoxicosis are characteristic. With insensitivity of the peripheral tissues of the body to thyroid hormones against the background of a normal level of thyroid-stimulating hormone and thyroid hormones, there are signs of hypothyroidism, that is, a reduced amount of thyroid hormones in the blood serum. The manifestations of hypothyroidism include: a gradual increase in body weight, dryness, thickening of the skin, a change in its color( "waxy", "peach" and "icteric" skin color), coarse facial features, shoe size increase, speech fuzziness. Periodically, especially after exercise, pain in the right upper quadrant, constipation, pain in the chest, dyspnea on walking may appear. In women, menstrual function is often impaired. You can note a significant decrease in intelligence.
The diagnosis of generalized resistance to thyroid hormones is made in the presence of three characteristic symptoms( triad): an increase in the content of thyroid hormone in the blood serum, normal or elevated thyroid-stimulating hormone, peripheral euthyroidism( normal thyroid hormone level in the blood) or hypothyroidismthyroid gland in the blood).People with this disease do not have such signs of thyrotoxicosis as weight loss, poor heat tolerance, trembling of the hands, irritability. Due to the compensatory increase in the level of thyroid hormones, people do not make complaints typical of hypothyroidism, since a high level of circulating thyroid hormones in the blood compensates for generalized insensitivity in most tissues of the body, thereby creating an euthyroid condition.
In persons with insensitivity to the pituitary gland( gland of the brain), the same disorders are noted in the blood, as in the generalized variant. The difference is that with this type of disease, they have signs and symptoms typical of thyrotoxicosis, such as weight loss, hand tremors, increased nervous excitability, increased heart rate, insomnia, poor heat tolerance. With the stability of the pituitary, its sensitivity to thyroid hormones decreases, and in normal peripheral tissues normal hormonal reactions are most often maintained.
Antenatal diagnosis of generalized resistance to thyroid hormones is based on the detection of mutations by the study of amniotic fluid.
Treatment. The vast majority of people with generalized resistance to thymus hormones have a normal or slightly elevated level of thyroid-stimulating hormone in the blood and significantly increased levels of thyroid hormones. Such people should not receive any treatment aimed at reducing the level of thyroid-stimulating hormone.
The drug of choice for pituitary resistance is triiodothyroacetic acid. The drug is taken in divided doses to achieve a permanent suppression of the secretion of thyroid-stimulating hormone. However, despite the suppression of its formation, the symptoms of thyrotoxicosis are partly preserved in the treatment with triiodothyroacetic acid.
The treatment and diagnostics of peripheral resistance( resistance) to thyroid hormones are the most difficult in connection with the actual absence of laboratory criteria, with the help of which it is possible to evaluate the adequacy of therapy with thyroxine( thyroid hormone).