Hypothyreose

Hypothyroidism is one of the most frequent endocrine disorders affecting 4.6% of the adult population. 90% of the cases represent subclinical hypothyroidism, defined by increased serum TSH but normal free thyroxine (fT4) values. General screening for hypothyroidism is not recommended because of lack of benefits for the patients. Search for hypothyroidism should therefore focus on patients with symptoms and signs and/or those presenting risk factors for development of hypothyroidism (e.g., autoimmune disorders, thyroid injury, post partum state). Because of the lack of specificity of sings and symptoms of this frequent disorder the diagnosis is based on measurement of TSH or TSH and fT4 in case of conditions that may affect TSH values such as non-thyroidal illness, or medications. Whereas primary hypothyroidism is due to lack of function of the thyroid itself and easy recognized by increased serum TSH, mild forms of secondary hypothyroidism may be difficult to detect because of the lack of function of the pituitary and thus absence of the best indicator of thyroid function. Here measurement of fT4 and a clinical assessment are the cornerstones for diagnosis of secondary hypothyroidism and monitoring of its treatment. In case of subclinical hypothyroidism defined as increased TSH but fT4 still within the normal laboratory range a TSH value above 10 mU/l is regarded as indication for treatment. For values between 4 and 10 mU/l an individualized pragmatic treatment approach based on the presence of clinical sings of hypothyroidism may be justified. Some patients however should be treated regardless of their clinical symptoms including women in childbearing age who want to become pregnant, patients with goitre, and patients with history of Graves disease. Treatment of hypothyroidism is best done with thyroxine (T4) alone; combination therapy of thyroxine with the active compound T3 does not have any advantage. The required L-T4 dose for optimal substitution (TSH between 0.5 and 2.5 mU/l) is in the range of 1.6 µg/kg body weight per day. In young subjects the starting dose should be close to the required dose i.e., 75 to 100 µg, elder patients and those with ischemic heart disease should start with lower doses (25 - 50µg). Pregnant women under L-T4 substitution should increase the dose by 25 % as soon as pregnancy is diagnosed.