Cushing's disease causes hypertension, hypokalemia, and alkalosis.
Am sure you are aware that ACTH has no control on zona glomerulosa and so no control on mineralocorticoids.
So Why?
Physiology did not answer this question with a solid evidence yet!
Some theories;
- Cushing's causes increased corticosterone and deoxy corticosterone seen in the aldosterone pathway and they have mineralocorticoid activity. That was suggested because they found that aldosterone receptor anatogonist did not ameliorate the hypertension seen in Cushing's.
- ACTH inhibits 11 Beta hydroxlase so in Cushing's this inhibition is lost (due to low ACTH), however, this theory was abandoned because hypokalemia was observed in Cushing's disease also (ectopic ACTH).
However, the most plausible and agreed upon explanation is that cortisol itself has some mineralocorticoid effects (that's why we see hypernatremia and hypokalemia in steroid therapy). Use this logic in answering your USMLE questions.