A 28-year-old man comes to the emergency department because of a severe headache, palpitations, excessive sweating, chest pain, visual disturbances, dyspnea. paresthesias, constipation, and a sense of impending doom over the past 2 weeks. These symptoms occur primarily at night. His blood pressure is 130/80 mmHg while supine and 90/60 mmHg while standing; his blood sugar is 240 mg/dL. Which of the following is the most likely diagnosis?

**Core Concept**
The patient's symptoms and blood pressure response suggest a diagnosis related to autonomic nervous system dysfunction, specifically a condition characterized by excessive sympathetic nervous system activity, particularly at night.

**Why the Correct Answer is Right**
The patient's presentation is classic for a pheochromocytoma, a rare tumor of the adrenal gland that secretes excess catecholamines (epinephrine and norepinephrine). These hormones stimulate the sympathetic nervous system, causing symptoms such as palpitations, excessive sweating, chest pain, visual disturbances, and a sense of impending doom. The nocturnal predominance of symptoms is a key feature of pheochromocytoma, as catecholamine levels typically rise at night due to the normal circadian rhythm of the adrenal gland. The blood pressure response to standing is also characteristic, as the patient's blood pressure drops due to vasodilation caused by excess catecholamines.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the patient's symptoms and blood pressure response. The patient's symptoms are not consistent with a diagnosis of acute coronary syndrome, which would typically present with chest pain, but not the other symptoms described.

**Option B:** This option is incorrect because the patient's blood sugar level is elevated, but the symptoms described are not typical of diabetes mellitus. The patient's symptoms are more consistent with a diagnosis of pheochromocytoma, which can cause hyperglycemia due to catecholamine-induced glycogenolysis.

**Option C:** This option is incorrect because the patient's symptoms are not consistent with a diagnosis of hypothyroidism. The patient's symptoms are more consistent with a diagnosis of pheochromocytoma, which can cause symptoms such as palpitations, excessive sweating, and chest pain.

**Option D:** This option is incorrect because the patient's symptoms are not consistent with a diagnosis of anxiety disorder. While the patient's symptoms may include a sense of impending doom, the presence of other symptoms such as palpitations, excessive sweating, and chest pain makes a diagnosis of pheochromocytoma more likely.

**Clinical Pearl / High-Yield Fact**
Pheochromocytomas are often associated with genetic syndromes such as multiple endocrine neoplasia (MEN) type 2 and von Hippel-Lindau disease. A family history of pheochromocytoma or other endocrine tumors should raise suspicion for a genetic syndrome.

**Correct Answer: D. Pheochromocytoma**

✓ Correct Answer: D. Pheochromocytoma