Hypothyroidism is the most common thyroid dysfunction. In most countries, particularly in Russia, hypothyroidism is due to iodine deficiency. The prevalence of hypothyroidism in the world is 5%.
The inability of the thyroid gland to produce enough hormones (T4 and T3) is the most common cause of hypothyroidism, called primary hypothyroidism . Secondary hypothyroidism is much less common. A significant part of cases of hypothyroidism is caused by the so-called autoimmune diseases of the thyroid gland – chronic lymphocytic thyroiditis and primary idiopathic hypothyroidism. (In the first case, there is goiter, in the second – atrophy of the thyroid gland.) Like other autoimmune diseases, they affect women much more often than men (8: 1).
Treatment of thyrotoxicosis is another common cause of hypothyroidism. Untreated congenital hypothyroidism leads to multiple developmental disorders known as cretinism.
Transient hypothyroidism is, by definition, the only reversible form of hypothyroidism. The frequency of postpartum thyroiditis , which occurs 1-6 months after birth, reaches 20%.
Manifestations of all forms of hypothyroidism are similar.
Common complaints include: rough skin, cold skin, pallor, sparse hair (hair loss), swelling around the eyes ( periorbital edema), low voice, goiter, swelling of the legs (this is the so-called mucous edema – it does not leave pits when pressed).
More rare complaints: slow speech, sleep apnea (respiratory arrest), low body temperature (hypothermia), hypertension, tongue enlargement ( macroglossia ), muscle pain (myopathy).
Complaints develop gradually, so hypothyroidism can last for years without a diagnosis. Since the disease affects many organ systems, most complaints are nonspecific. In addition, the severity of symptoms does not always correspond to the severity of the disease. Even in patients with laboratory signs of hypothyroidism, complaints may be absent. Weakness, drowsiness, constipation, dry skin, hair loss – these are the most common non-specific symptoms of hypothyroidism. Specific signs of hypothyroidism include chilliness, puffiness of the face, coarsening and a decrease in the timbre of the voice.
Some manifestations of hypothyroidism are age dependent. In children, this is growth retardation, in women of childbearing age – menstrual irregularities, in the elderly – dementia. The most characteristic feature of hypothyroidism is an extension of the relaxation phase of tendon reflexes, primarily of the Achilles reflex (often a neurologist may suspect hypothyroidism). Often there is a pleural or pericardial effusion, sometimes significant.
Since 95% of patients have primary hypothyroidism, it is best to start by determining thyroid stimulating hormone (TSH). Elevated TSH in the blood is the most sensitive indicator of hypothyroidism. A moderate increase in TSH (usually within 15 mIU / L) is often observed against the background of normal T4 levels; in such cases, they speak of latent hypothyroidism. There is currently no single point of view regarding the treatment of practically healthy people with latent hypothyroidism.
Since the main symptom of hypothyroidism is a decrease in thyroid hormone levels, a measurement of T4 level is indicated. The measurement of total T3 in the diagnosis of hypothyroidism is insensitive and almost never used. In the vast majority of cases, the diagnosis of hypothyroidism can be established by the clinical picture, T 4 and TSH. Determination of antithyroid antibodies helps to establish the cause of hypothyroidism, as well as to identify individuals who are at increased risk of converting latent hypothyroidism into a clinically expressed one. Thyroid scintigraphy is almost never needed. It is used only to confirm abnormalities in the development of the thyroid gland and to study nodular goiter.
Synthetic T4 – levothyroxine (L-thyroxine, Eutirox ) – the main drug in the treatment of hypothyroidism. The content of levothyroxine in drugs of different companies is standardized, however, experience suggests that the patient should use the same drug (due to small differences in the content of the active substance in drugs of different manufacturers). The usual replacement dose is 75-150 mcg per day. The correct selection of the dose is controlled by the level of TSH. After changing the dose of the drug, a new stationary state is established no earlier than after 4-6 weeks. Until this time, measuring TTG does not make sense. The goal of levothyroxine replacement therapy is to achieve a normal TSH level, since an overdose of levothyroxine and, therefore, a drop in TSH levels below normal lead to a decrease in bone density. When a normal TSH level is reached, to assess the correctness of the replacement therapy with levothyroxine, it is sufficient to determine the TSH every 6-12 months.