[Thyrotropic deficiency]

Central hypothyroidism (thyrotropic deficiency) is due to a defect in TSH secretion by thyrotrophs (or alternatively to an altered bioactivity of TSH). Central hypothyroidism is rare and is often associated with other pituitary deficiencies as it is generally encountered in case of hypothalamo-pituitary tumoral process. Clinical symptoms are milder than those of primary thyroid failure. Diagnosis is based on free T4 measurement whose level is decreased while TSH concentration is normal or minimally increased, reflecting an alteration in the bioactivity of TSH. Replacement therapy is monitored by T4 level measurement: the objective is to obtain normal T4 levels. TSH concentration must not be taken into account for the adjustment of the thyroxine doses.