What is the most likely diagnosis for a 23-year-old woman with secondary amenorrhea, dark neck pigmentation, severe acne, and low potassium?

The symptoms presented in this case—the combination of secondary amenorrhea, dark neck pigmentation, severe acne, and low potassium—strongly suggest Cushing's syndrome as the most likely diagnosis.

Cushing's syndrome is characterized by excess cortisol, which can be caused by various factors, such as a pituitary adenoma (Cushing's disease), adrenal tumors, or ectopic ACTH production. One of the hallmark features of Cushing's syndrome is the distinctive physical changes it causes, including the development of hirsutism and severe acne due to androgen excess, which aligns with this patient’s presentation.

The dark neck pigmentation can indicate a condition known as hyperpigmentation, which is sometimes seen in Cushing’s syndrome due to cortisol's interaction with the skin. The presence of low potassium is particularly telling, as hypokalemia can arise from the mineralocorticoid effects of excess cortisol, which leads to increased sodium retention and potassium secretion.

Given these clinical signs, the diagnosis of Cushing's syndrome fits best with the combination of secondary amenorrhea, severe acne, and low potassium levels, distinguishing it effectively from the other conditions listed. For instance, acquired hypothyroidism typically presents with symptoms like fatigue, weight gain, and cold