Improvement of hypothyroidism after glucocorticoid replacement in isolated adrenocorticotropin deficiency

We report a 50-year-old female who suffered from reversible hypothyroidism accompanied by isolated ACTH deficiency. There were no findings indicating a complication of autoimmune thyroiditis. Replacement of maintenance dose of glucocorticoid not only led to improvement of thyroid function, but also caused a transient decrease in T 3 and an increase in reverse T 3 , suggesting that chronic cortisol deficiency may impair thyroid function, and that the maintenance dose, as well as pharmacological doses of glucocorticoids may influence T 4 deiodination. The findings of this case suggest that thyroid function should be re-evaluated to avoid unnecessary replacement of thyroid hormone, a few months after glucocorticoid replacement.