Abstract
A three-month-old boy presented congenital hypopituitarism in which the hypothyroid state masked ACTH deficiency. Multiple anterior pituitary hormone deficiencies, including ACTH, were finally confirmed. High basal serum cortisol levels (up to 45.1μg/dl) were observed during a stressful episode before L-thyroxine replacement therapy was started. Decreased morning serum cortisol levels (5.0μg/dl or below) were observed on the sixth day of L-thyroxin replacement therapy despite mild hypoglycemia (lowest serum glucose level of 50mg/dl). ACTH deficiency was then confirmed by insulin-induced hypoglycemia test (peak serum cortisol level of 4.9μg/dl). The present findings showed that serum cortisol levels can be high during a stressful episode in an infant with ACTH deficiency and a coexisting hypothyroid state. Thus, the diagnostic evaluation of adrenal function soon after L-thyroxine replacement therapy is important in order to verify a possible subclinical ACTH deficiency, even in the presence of high serum cortisol levels before L-thyroxine replacement therapy.
