**Core Concept**
Adrenal hyperfunction, particularly Cushing's syndrome, is characterized by excessive production of cortisol from the adrenal glands. This leads to a range of systemic effects, including weight gain, abnormal menstrual cycles, and skin changes such as purplish striae.

**Why the Correct Answer is Right**
The elevated cortisol secretion in this patient is likely due to an adrenal tumor or hyperplasia, leading to autonomous cortisol production. This can result in a variety of clinical manifestations, including **hypokalemia**. Cortisol promotes the excretion of potassium in the urine, leading to decreased serum potassium levels. Additionally, cortisol can cause sodium retention, further contributing to hypokalemia.

**Why Each Wrong Option is Incorrect**
**Option A:** Osteoporosis - While Cushing's syndrome can lead to bone loss, it is not a direct consequence of adrenal hyperfunction.
**Option B:** Hypokalemia - This is the correct answer, as explained above.
**Option C:** Hypothyroidism - There is no evidence to suggest thyroid dysfunction in this patient, as TSH and thyroid hormone levels are normal.

**Clinical Pearl / High-Yield Fact**
Cushing's syndrome can be remembered as "moon face, buffalo hump, and purple striae" - a classic clinical triad of weight gain, skin changes, and purplish striae.

**Correct Answer:** B. Hypokalemia.