DEFINITION
Hypothyroidism is a morbid condition caused by a lack of thyroid hormones (T3 and T4) or a lack of their effect on target tissues (TH resistance).
The disease definition according to a specific consensus conference or to The Diseases Database based on the Unified Medical Language System (NLM)
EPIDEMIOLOGY
The hypothyroidism is commonly in the elderly. The increased frequency is observed in women. Prevalence over 60 years is the 1.5-2%.
It may already be present at birth and determine, if not promptly treated, serious problems of intellectual and physical development (cretinism sporadic), now easily preventable through the tests that are found all the babies to see if their thyroid is well developed during the pregnancy and especially function normally at birth (neonatal screening of hypothyroidism)
Thanks to improved social conditions and health, a diet richer and more balanced - even with the use of iodized salt (iodine prophylaxis) - Neonatal screening and advances in the diagnosis and treatment of thyroid diseases, today these serious forms of hypothyroidism in early childhood onset are actually missing.
Remains very frequently hypothyroidism in:
- children of school age
- adolescents
- adults
In these cases the hormonal deficiency appears in a body already more or less fully developed, particularly in the brain, and therefore does not give cretinism. Are present goiter other disorders more or less severe. If not properly treated, hypothyroidism can impair the efficiency of the whole body.
The disease is found:
- Europe
- North America
- Nepal
- New Guinea
- Zaire
In some countries, including Italy, hypothyroidism from lack of iodine in the diet is still quite common, even in children and adolescents. Over 10 million Italians are suffering because of goiter endemic iodine deficiency. One problem not yet solved, so that was recently approved by Parliament a law to encourage the consumption of iodized salt in place of common table salt. The use of salt enriched with iodine in the preparation and storage of foods is an effective form of prophylaxis of endemic goiter.
SYMPTOMS
Symptoms affect all the organs because they are all
sensitive to hormone (Symptoms)
In some ways the most serious one has the so-called facies myxedematosa, resulting in swelling of the face and is due mainly to an increase of interstitial fluid in skin tissue.
The myxedema is a hard swelling which can affect:
- mouth (swelling)
- vocal cords (deterioration of the voice becomes throaty)
- skin and appendages (hair loss, dry skin)
- yellowing of the skin (palms of the hands and soles of the feet).
- goitre may be present, if the cause is due to an altered synthesis of thyroid hormones, for example, to lack of iodine. In some patients the goitre disorders may give local compression, especially if you have retrostenal extension. In this case you can have compression and displacement of the trachea or esophagus, the patient complains of difficulty swallowing solid foods.
Myxedema coma
It’s a serious medical condition that appears rarely, is exceptionally the final stage of hypothyroidism, occurs most often after prolonged exposure to cold, infections and trauma, or following ingestion of sedative drugs.
Symptoms:
- slowed heart rate
- hypothermia (body temperature below 34 ° C)
- somnolence gradually until coma.
- cardiomegaly
- bradycardia
- abnormalities of the genital tract, with decreased libido in men and women, and abnormal menstrual cycle
- muscle fatigue
- alterations of the skeleton (hypothyroidism occurs during childhood)
DIAGNOSIS
The symptoms are not sufficient to make diagnosis, but must be used at a dose of thyroid hormones.
Laboratory tests:
- thyroid hormone dosing: FT3 and FT4 (reduced); thyrotropin, TSH (increased)
In patients where there is evidence of low FT4 and normal or low TSH, you should seek a secondary hypothyroidism with interest then of hypothalamus and pituitary. In this case the tests are made more complicated, one of which is the Test to TRH
- antithyroid antibodies: antithyreoglobulin and antiperoxidase to search for an autoimmune involvement, as in thyroiditis.
- complete blood count:hypercholesterolemy, anaemia (reduction of hemoglobin values)
PATIENT RISK FACTORS
Vascular
Genetic
Acquired
Hormonal
Genetic
Acquired
TISSUE SPECIFIC RISK FACTORS
anatomical (due its structure)
vascular (due to the local circulation)
physiopathological (due to tissue function and activity)
PATHOGENESIS
The system includes hypothalamus -> pituitary -> thyroid -> liver -> receptors
tissue (muscle, liver, heart etc) any alteration in one of these points induces different disease:
- hypothalamus and pituitary
- mutated gene for the hypothalamic receptor -> thyroid hormones act through negative feedback on hypothalamus and pituitary tying a subtype of THRB that could be mutated
- levels of thyroid hormones slightly subnormal -> increase secretion of TSH from the pituitary gland
- lesion -> hormone insufficient respectively TRH and TSH hormone, resulting in reduced incentives for the production of thyroid hormones (secondary hypothyroidism)
- thyroid
- development of congenital deficiency of thyroid gland -> at birth there is a reduced mass of thyroid tissue; during fetal life and neonatal deficiency of thyroid hormones causes a developmental delay of the central nervous system
- autoimmune processes -> body due to an infection of the thyroid (Hashimoto thyroiditis) produces antibodies against its own thyroid tissue. The thyroid gland becomes fibrotic and has a low volume, the synthesis function is impaired.
- post-treatment -> reduction of thyroid tissue due to thyroid surgery or radiation therapy with radio-iodine, used in hyperthyroidism; also use of drugs antithyroid
- iodine deficiency, or intake of high amounts of iodine in the form of drugs (it's content, for example, in the cough syrups) or dietary supplements.
- selenium deficiency
- changes in the proteins necessary for synthesis of biochemical processes of thyroid hormones
- lack of conversion of T4 to T3 in the liver, but is not documented in humans or animals. Low T3 with normal T4 values are often due to concomitant disease (euthyroid syndrome) or administration of drugs:
- amiodarone
- lithium
- propranolol
- corticosteroids
- contrast media iodates
TREATMENT
Thyroid Hormone Replacement Therapy
Laura Piredda e Marzia Pera