Situation: A 49-year-old man with acromegaly from a growth hormone–secreting pituitary adenoma undergoes transsphenoidal removal of the tumor. He returns to the surgical ward with nasal packing and an indwelling urinary catheter. On the third postoperative day, his morning serum cortisol and free thyroxine (T4) are both low, consistent with new hypopituitarism. He is alert, and his blood pressure is 104/66 mmHg. The provider plans to replace both hormones. Which plan is BEST?

When both the cortisol and thyroid axes are deficient, glucocorticoid is replaced first. Thyroid hormone speeds cortisol clearance and raises metabolic demand, so starting it first in a client with untreated adrenal insufficiency can precipitate adrenal crisis.

Core physiologic principle
When both the adrenal axis and the thyroid axis fail together, the replacement sequence is not interchangeable. Cortisol deficiency slows the hepatic and renal clearance of thyroxine, while thyroid hormone accelerates cortisol breakdown and raises tissue demand for glucocorticoid. If levothyroxine is started first in a patient with untreated secondary adrenal insufficiency, the resulting increase in cortisol metabolism can unmask or precipitate adrenal crisis, which may present as refractory hypotension, hypoglycemia, or cardiovascular collapse. Therefore, glucocorticoid replacement must be established before thyroid hormone is introduced.

Why this patient is at risk
This 49-year-old man underwent transsphenoidal removal of a growth hormone–secreting pituitary adenoma. On postoperative day 3, his morning serum cortisol and free T4 are both low, indicating new-onset hypopituitarism involving at least the corticotroph and thyrotroph axes. His blood pressure of 104/66 mmHg is still within an acceptable range, and he is alert, but this does not rule out clinically significant adrenal insufficiency. Early postoperative hormone deficiencies are a recognized complication of pituitary surgery, and the immediate postoperative window is the highest-risk period for decompensation.

Replacement sequence in combined deficiency
The safest plan is to start hydrocortisone now and add levothyroxine later, once glucocorticoid coverage is stable. Hydrocortisone provides both glucocorticoid and some mineralocorticoid activity, which helps maintain vascular tone and blood pressure. After cortisol replacement is underway, levothyroxine can be introduced at a low dose and titrated gradually, with monitoring of free T4 and clinical status. This sequence prevents the thyroid hormone from acutely increasing cortisol clearance before adequate exogenous cortisol is available.

Option	Problem	Physiologic consequence
1 Levothyroxine alone, recheck cortisol in 6 weeks	Thyroid hormone started first in untreated adrenal insufficiency	Accelerated cortisol clearance; risk of adrenal crisis
2 Hydrocortisone now; add levothyroxine later	Correct sequence	Establishes cortisol coverage before thyroid replacement
3 Delay both hormones until repeat pituitary scan	Unnecessary delay in hormone replacement	Prolonged exposure to cortisol and thyroid deficiency
4 Levothyroxine now; add hydrocortisone if hypotensive	Reactive rather than preventive approach	Hypotension may be a late sign of adrenal crisis

Clinical monitoring and timing
In the early postoperative period, cortisol and free T4 should be checked promptly, as was done here. The finding of low values on day 3 supports the diagnosis of new hypopituitarism rather than a transient perioperative suppression alone. Hydrocortisone is typically given in divided doses to mimic the normal diurnal rhythm, with a higher morning dose. Levothyroxine is added after the patient is clinically stable on glucocorticoids, usually within days to a few weeks, and the dose is adjusted based on free T4 levels and clinical response. Watch out! A normal blood pressure does not exclude adrenal insufficiency; hypotension is a late and unreliable indicator. Key point! In combined ACTH and TSH deficiency, glucocorticoid replacement always precedes thyroid hormone replacement.