**Core Concept**
Pheochromocytoma is a rare, usually benign, tumor of the adrenal gland that secretes excessive amounts of catecholamines, such as epinephrine and norepinephrine. The clinical presentation of pheochromocytoma is primarily due to the effects of these hormones on the body's sympathetic nervous system.

**Why the Correct Answer is Right**
The predominant symptom of pheochromocytoma is episodic hypertension, which occurs due to the sudden release of catecholamines from the tumor. This leads to a transient increase in blood pressure, often accompanied by symptoms such as palpitations, headache, and sweating. The episodic nature of the hypertension is due to the intermittent secretion of catecholamines, which can be triggered by various factors such as stress, exercise, or changes in posture.

**Why Each Wrong Option is Incorrect**
**Option A:** Sweating is a common symptom of pheochromocytoma, but it is not the predominant symptom. Sweating occurs due to the activation of the sympathetic nervous system by catecholamines, but it is usually accompanied by other symptoms such as hypertension and palpitations.
**Option B:** Weight loss is not a typical symptom of pheochromocytoma. In fact, some patients may experience weight gain due to the increased appetite and metabolic rate caused by excess catecholamines.
**Option C:** Orthostatic hypotension is not a characteristic symptom of pheochromocytoma. While some patients may experience orthostatic hypotension due to the autonomic nervous system dysfunction caused by catecholamine excess, it is not a common feature of the disease.

**Clinical Pearl / High-Yield Fact**
The classic triad of symptoms associated with pheochromocytoma is episodic hypertension, palpitations, and sweating. However, not all patients will exhibit all three symptoms, and the diagnosis often requires a high index of suspicion and supportive laboratory findings.

**✓ Correct Answer: D. Episodic hypertension**