Thyrotropic insufficiency

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Thyrotropic insufficiency, also known as thyrotrophic insufficiency or thyrotropic deficiency, is partial insufficiency of the anterior pituitary or the respective component of total hypopituitarism, where deficient thyrotropin secretion leads to anderstimulation of the thyroid gland with consecutive secondary hypothyroidism.

Contents 1 Classification 2 Etiology 3 Diagnosis 4 Therapy

Classification

Depending from severity the following types are differentiated:

• partial thyrotropic insufficiency with residual pituitary function:
  • Type 1 (Early phase: TSH reduced, FT4 normal)
  • Type 2 (Later phase: TSH normal, FT4 reduced)
• complete thyrotropic insufficiency (TSH and FT4 reduced).

Etiology

Thyrotropic insufficiency may be caused by the following disorders:

• Pituitary apoplexy
• Pituitary adenoma
• Pickardt-Fahlbusch syndrome
• Hypothalamic damage (with consecutive tertiary hypothyroidism)
• Craniocerebral injury
• Hypophysitis

Diagnosis

Thyrotropic insufficiency is diagnosed by TRH test or by calculating Jostel's TSH index.

Therapy

Treatment relies on substitution with thyroxine. However, the substitution dose is adjusted in dependence from FT4 levels and not (as usual in primary hypothyroidism) from TSH levels.