Lhypothyroïdie

Hypothyroïdie, in English hypothyroidism and in French l’hypothyroïdie, is a medical condition in which the thyroid gland does not produce enough thyroid hormones. The deficiency of thyroxine (T4) and triiodothyronine (T3) slows many body processes. Primary hypothyroidism is the most common form; secondary or tertiary hypothyroidism results from pituitary or hypothalamic disease. The condition is more common in women and often develops with age or after thyroid surgery, radioactive iodine treatment, or autoimmune disease.

Symptoms include fatigue, weight gain, cold intolerance, dry skin and hair, constipation, slowed heart rate, menstrual irregularities, memory problems, and depression. Some people have few symptoms early on, making diagnosis based on blood tests.

Diagnosis relies on blood tests showing elevated thyroid-stimulating hormone (TSH) and low free thyroxine (free T4). Anti-thyroid antibodies may be present in autoimmune thyroiditis (Hashimoto’s). In secondary hypothyroidism TSH can be low or normal.

Treatment is lifelong thyroid hormone replacement with levothyroxine. The dose is individualized to restore TSH to the reference range and is often adjusted after starting therapy or during pregnancy. Dosing considerations include timing on an empty stomach and avoidance of certain supplements.

Monitoring involves measuring TSH 6–8 weeks after dose changes, then every 6–12 months once stable. Subclinical hypothyroidism features elevated TSH with normal free T4 and may be observed or treated depending on risk factors.

Pregnant people require higher doses; treated hypothyroidism improves fetal development and outcomes. In newborns, screening detects congenital hypothyroidism early. Untreated hypothyroidism can lead to cardiovascular problems, lipid abnormalities, infertility, and, in severe cases, myxedema coma.