Hypothyroidism is essentially a deficiency of thyroid hormones, due to primary thyroid causes, secondary or tertiary (central).
Hypothyroidism is a condition of thyroid hormone deficiency, the causes of which can be primary, secondary, and tertiary (central). The most common cause of hypothyroidism is Hashimoto’s autoimmune thyroiditis. Symptoms are often implicit and slow to develop over time. Strict control of hypothyroidism before and during pregnancy, as well as in young women of childbearing age, is extremely important.
Hypothyroidism is insufficient production of thyroid hormones by the thyroid gland, the most common cause of which is compromised thyroid gland production. According to its etiology, hypothyroidism can be divided into congenital, primary (autoimmune genesis, iodine deficiency, overexposure with thyrostatic agents, resection of the thyroid gland, radiation therapy, etc.); and secondary (associated with hypothalamic-pituitary causes, very rarely).
The clinical picture of hypothyroidism is often implicit, slowly developing over time – weakened physical and mental potential, chronic fatigue and drowsiness, apathy and depression, chills, chronic constipation, cold, pale and dry skin, swelling (especially in the malar area and limbs, but also diffuse), weight gain, dysmenorrhea, sterility, hypotension, bradycardia, weakened tendon reflexes, etc.
In advanced, severe forms, pericardial effusions, ventricular pseudohypertrophy (due to interstitial edema), myxedema coma, etc. can be observed.
Laboratory tests often show hypercholesterolemia and normochromic anemia. In addition to the specified specific cardiac manifestations, low-voltage QRS complexes, as well as negative T waves in V1-V3 leads, are often observed on the ECG. Of course, this is not a specific criterion for the diagnosis and can be observed even with ischemia, as well as with a juvenile type of ECG (more often young women), but it is an interesting finding.
The most common cause of primary hypothyroidism is Hashimoto’s autoimmune thyroiditis. The etiology of the disease is insufficiently understood – both genetic and hereditary factors play a role (the female sex is more prone to the disease, and if there is a family history, annual screening is required after the age of 12), and external environmental factors (infections – viral EBV, herpes zoster, etc.; emotional stress, etc.).
Pathogenetically, lymphocyte infiltration is observed. Screening is sufficient to establish adequate TSH values to rule out the diagnosis. High TSH values (negative feedback) are associated with decreased serum levels of thyroid hormones, and their quantitative study is also necessary. Normal values of thyroid hormones and an increase in TSH are indicative of latent hypothyroidism, which requires follow-up and timely treatment. To confirm the autoimmune genesis of hypothyroidism, a study of MAT and TAT antibodies is necessary. Ultrasound examination of the thyroid gland is also of central importance in establishing the diagnosis and monitoring the course of the disease – atrophy of the thyroid gland, fibrous changes, etc. are observed.
In the presence of thyroid deficiency (reduced peripheral levels of ft3 and ft4), replacement treatment with L-thyroxine is necessary, the dose being titrated, depending on the severity of the deficiency. This is extremely important in pregnant and young women of childbearing age, as in this group of patients, as well as before a planned pregnancy, it is necessary to maintain TSH values around and below 2.5 mU/l.
During pregnancy itself, strict control and titration of the dose monthly is necessary, since thyroid deficiency is associated with higher neonatal mortality, high frequency of spontaneous abortions, premature birth, respiratory distress syndrome, and general delayed development of the child. During the first trimester of pregnancy, the fetus’s thyroid gland is not functioning and it draws entirely on thyroid hormones from the mother. That is why the needs suddenly jump 3-5 times and a timely titration of the mother’s dose is necessary. In the first trimester, the desired TSH values are below 2.5 mU/l, even below 2. In the second and third trimesters, values up to 3 can be tolerated.
Other causes of hypothyroidism are idiopathic hypothyroidism (with unclear etiopathogenesis, non-autoimmune), resections of the thyroid gland and operative interventions in the area, radiation therapy, and overdose with hydrostatics. A rare cause is Riedel‘s fibrosing thyroiditis.
A less common cause of hypothyroidism is secondary hypothalamic-pituitary hypothyroidism, in which due to reduced production of TRH and TSH, thyroid deficiency is observed (central hypothyroidism). Etiologically, the causes of central hypothyroidism are different – resections of the pituitary gland and operative interventions in the area; tumors (primary, central – macroadenomas, craniopharyngiomas, meningiomas, etc.; metastatic lesions – in lung and breast cancer, etc.), aneurysms, hemorrhages, pituitary apoplexy, infectious causes (abscesses, syphilis, tuberculosis, etc.) , iatrogenic causes (glucocorticoids, somatostatin, growth hormone, etc.), genetic causes (TRH deficiency, inactive forms of TSH, inactivating mutations in TRH receptors. Usually, the diagnosis of central hypothyroidism is delayed due to decreased or normal TSH values.
Making the diagnosis is complex – laboratory, low or normal values of TSH and reduced values of ft3 and ft4 are indicative. The so-called TRH test, in which synthetic TRH is administered intravenously to the patient, and TSH values are examined at 20 and 60 minutes. A normal response is the presence of higher TLC values at 20 minutes. In central hypothyroidism, there is a “plateau” type response or higher TSH values at 60 minutes. The central causes of hypothyroidism are much rarer but should be considered in the differential diagnosis when establishing low TSH values.
In conclusion, hypothyroidism is a chronic disease with a slow course and an implicit picture. The prognosis is good and life expectancy is unchanged with good control. Strict control during and several months before pregnancy is extremely important in women with hypothyroidism, as well as in those of young childbearing age.
