Diagnosis and Management of Hypothyroidism in Adults

Abstract

Hypothyroidism is one of the most common endocrine disorders, defined as deficient production of thyroid hormones. In primary hypothyroidism, there is a thyroidal defect in the thyroid gland and decrease in thyroid hormones leads to an increased TSH secretion; in central hypothyroidism, there is either an insufficient thyroid stimulation by TSH (secondary hypothyroidism = pituitary causes) or an insufficient hypothalamic TRH release (tertiary hypothyroidism = hypothalamic causes). The disease is more frequent in women than in men; it affects all ages, but is more frequent in middle-age patients. Incidence varies between 0.6/1000/year in men and up to 4.1/1000/year in women. Primary hypothyroidism is the most frequent, caused by chronic autoimmune thyroiditis, thyroid surgery and radioiodine (¹³¹I) ablation, external radiotherapy, thyroid dysgenesis, defects in thyroid hormones biosynthesis, release and action, and drugs. Symptoms include: fatigue, cold intolerance, weight gain, dry skin, constipation, muscle weakness, impaired memory, etc. Signs include: dry skin, carotenemia, puffy facies and loss of eyebrows, edema, bradycardia, diastolic hypertension, bradylalia, bradykinesia, etc. For diagnosis, TSH and free thyroxine (FT₄) are mandatory. TSH is the screening and first-line diagnostic test for primary hypothyroidism; FT₄ is necessary for diagnosis of central hypothyroidism and for diagnosis of overt versus subclinical primary hypothyroidism. Treatment consists in administration of levothyroxine (LT₄), orally, once daily, aiming to normalize serum TSH, to restore patients’ physical and psychological well-being, and to avoid overtreatment. In first-term pregnant women, TSH should be kept <2.5 mIU/L; in second and third trimesters of pregnancy, TSH should be <3 mIU/L.