A 34-year-old man with no previous medical history comes to the clinic due to worsening headaches and dizziness. The headaches tend to occur during periods of stress and are sometimes associated with blurry vision and nausea. The patient does not use tobacco, alcohol, or illicit drugs. Blood pressure is 170/100 mm Hg supine and 150/90 mm Hg standing 2 minutes, and pulse is 90/min and regular. BMI is 24 kg/m². The remainder of the physical examination is unremarkable. Fasting laboratory results are as follows: Which of the following investigations should be ordered next?

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11ec25c8_d21f_d0b1_bc81_c7c57674f924_MD0003_00 This patient's hypertension, episodic headaches, and unexplained hyperglycemia should raise suspicion for pheochromocytoma. Pheochromocytomas are rare neuroendocrine tumors that arise from chromaffin cells and release excess catecholamines (ie, dopamine, epinephrine, norepinephrine) into the bloodstream, resulting in characteristic manifestations. Headaches are often episodic and present in 90% of patients. Paroxysmal hypertension occurs in approximately half of patients and may be associated with orthostasis (possibly reflecting low plasma volume). Vision changes, coinciding with episodes of headache and hypertension, can also occur. Because catecholamines inhibit insulin secretion, hyperglycemia is also common. Therefore, pheochromocytoma should be considered in patients who develop hyperglycemia that is atypical for both type 1 (ie, usually presents with diabetic ketoacidosis) and type 2 (ie, rarely occurs in patients age <35 with normal BMI, as in this patient) diabetes mellitus, especially when accompanied by other suggestive features, such as onset of hypertension (particularly at a young age). Other indications for screening include: the classic triad of headache, sweating, and tachycardia; resistant hypertension; or a familial syndrome (eg, multiple endocrine neoplasia type 2). The initial step in evaluation for pheochromocytoma involves testing for urine or plasma levels of metanephrines, which are products of catecholamine breakdown. Normal levels typically rule out the disease; elevated levels are nonspecific and warrant additional testing, such as CT scan of the abdomen (Choice A), to confirm the presence and localization of the suspected pheochromocytoma (usually on one or both adrenal glands). (Choice B) CT scan of the head is typically indicated for headaches only when red-flag features (eg, focal neurologic deficits, fever, new-onset headache in patient age >50) are present. (Choice C) Dexamethasone suppression testing is indicated for suspected hypercortisolism (ie, Cushing syndrome). Although hypertension and hyperglycemia are common, patients are usually overweight and have characteristic findings on physical examination (eg, purple abdominal striae, fat pad on the upper back). (Choice E) Renal vascular imaging may help diagnose fibromuscular dysplasia, which typically presents with headaches and can cause hypertension. However, fibromuscular dysplasia usually occurs in women and would not explain this patient's hyperglycemia. (Choice F) A serum glucagon level is indicated for suspected glucagonoma. Although a glucagonoma would cause hyperglycemia, it would not explain hypertension, episodic headaches, and vision changes. Educational objective: Pheochromocytoma commonly presents with episodic headaches and hypertension and can cause unexplained hyperglycemia. Measurement of urine or plasma metanephrines is the initial step in diagnostic evaluation. References: Prevalence of clinically unsuspected pheochromocytoma. Review of a 50-year autopsy series. (http://www.ncbi.nlm.nih.gov/pubmed/6453259)

A 34-Year-Old Man with No Previous Medical History Comes to the Clinic