Central hypothyroidism: consequences in adult life

Central hypothyroidism (CH) is a rare cause of hypothyroidism, generally due to either pituitary or hypothalamic defects. On the basis of its etiology, it is possible to distinguish acquired and hereditary forms. Hereditary CH can be isolated or associated with combined pituitary hormone deficiency (CPHD). In the former case, alterations of only two genes, TSHbeta and the TRH receptor, have so far been described as responsible for the disorder. In hereditary CH associated with CPHD, inactivating mutations of different pituitary transcription factors (HESX1, PROP-1, POU1F1) have been found involved in the pathogenesis of the disease. Finally, an association between CH and severe obesity has been described in patients with leptin receptor (Leptin-R) mutations. The clinical consequences of CH in adult life vary greatly depending on the etiology, the severity of the thyroid impairment, the extent of the associated hormone deficiencies, and the age of the patient at the time of the onset of the disease. In general, acquired CH is less severe than the congenital form because of the constitutive activity of the wild-type TSH-receptor. Symptoms and signs of thyroid insufficiency are usually milder than those of primary hypothyroidism, and goiter is always absent. In CPHD, most patients have other endocrine manifestations of the disease (growth failure, delayed puberty, adrenal insufficiency, diabetes insipidus) that lead them to seek medical attention before the hypothyroidism becomes severe. Early diagnosis of the congenital form by neonatal screening for hypothyroidism is strongly recommended in order to avoid cretinism. Replacement therapy with L-thyroxine administration has to be established as soon as possible.