The clinical signs of a patient with thyrotrophin deficiency are the same as a patient with hypothyroidism of primary thyroidal origin (see thyroid section). Thyrotrophin is very rarely deficient by itself and is usually associated with a deficiency in other adenohypophysial hormones.
The main aim in the diagnosis of thyrotrophin deficiency is to distinguish it from the hypothyroidism of primary thyroidal origin. The key to the diagnosis is that in hypothyroidism of primary thyroidal origin, the low plasma T4/T3 levels are associated with high levels of TSH. In thyrotrophin deficiency, the low T3/T4 levels are associated with low levels of TSH.
The aim of the treatment is to treat the hypothyroidism with thyroxine. There is one exception to this rule:
In patients who have concurrent thyrotrophin and corticotrophin deficiency, thyroxine must not be given without cortisol as it may precipitate a 'pituitary crisis'.