Remember that prolactin is inhibited by dopamine!
In panhypopituitaryism, the anterior pituitary hormones are more commonly affected than the posterior pituitary hormones and there is a spectrum for how much of the HPA axis is still preserved depending on the etiology of the panhypopituitaryism.
The hormones that need replacement in adults are T4 and cortisol. Testosterone can be replaced if needed in men. Estrogen and progesterone can be replaced in pre-menopausal women who do not want fertility at that time or in post-menopausal women to relieve post-menopausal symptoms. If a woman desires fertility and has enough HPA axis preserved then patients can get pulsatile GnRH to stimulate FSH and LH production to induce ovulation.
To screen for adrenal insufficiency, check a morning cortisol at 8am.
- Cortisol < 3 = likelihood high – check ACTH to determine primary versus secondary adrenal insufficiency
- Cortisol 3-18 = indeterminate – do further stimulation testing
- Cortisol > 18 = likelihood low – pursue other diagnosis
- Cosyntropin test – give cosyntropin (synthetic ACTH) and then measure cortisol level 1 hour later – normal is cortisol level > 18; if less than that, then likely primary adrenal insufficiency
- Insulin induced hyperglycemia test – give 0.1U/kg of insulin and check glucose at 15, 30, 60, 90, 120 minutes. Once glucose reaches < 50 then cortisol should be > 18
- Metyrapone testing – blocks 11B hydroxylase which leads to a drop in cortisol and increase in ACTH and increase in 11-deoxycortisol
- Insufficient dosing of steroids
- Failure to increase dosage of steroids with acute illness
- Persistent vomiting or diarrhea causing malabsorption of steroids
- Can commonly see isolated ACTH presentation in panhypopituitaryism
- Dexamethasone if adrenal insufficiency not yet diagnosed because it does not interfere with cortisol testing
- Hydrocortisone if pre-existing diagnosis
Remember – if you suspect adrenal insufficiency, give stress dose steroids immediately without waiting for further testing!