Thyroid hormone replacement in hypopituitarism

For patients with hypothyroidism secondary to hypopituitarism, the thyroid hormone thyroxine (T₄) is replaced rather than the pituitary hormone, thyroid stimulating hormone (TSH). Lifelong thyroid replacement therapy is needed for patients with TSH deficiency.

Do not start thyroid replacement therapy before excluding or correcting coexisting glucocorticoid deficiency—levothyroxine increases the clearance of cortisol, and can precipitate adrenal crisis in a patient with low glucocorticoid reserve.

Note: To avoid adrenal crisis, do not start thyroxine replacement therapy in hypopituitarism before correcting coexisting glucocorticoid deficiency.

The principles of initial replacement of T₄ are the same as those in primary hypothyroidism, but the dose of levothyroxine must be adjusted based on clinical features and serum T₄ concentration, not serum TSH concentration. A low serum TSH concentration is an expected finding in hypothyroidism secondary to hypopituitarism, and is not a basis for reducing the levothyroxine dose. Aim for a serum T₄ concentration in the upper half of the reference range. For doses and information about starting thyroxine replacement therapy in adults, see here, and for children, see here.