A 35-year-old woman presents to the urgent care clinic for evaluation of headache and episodes of heart palpitations which began 4 months ago. These symptoms are accompanied by sweating. Her medical history is significant for a copper intrauterine device (IUD) implanted 2 years ago. She does not smoke cigarettes and drinks 6-7 glasses of wine per month. Her blood pressure in the clinic is 190/135 mmHg, pulse is 117 beats/minute. Physical examination is significant for tachycardia, generalized skin pallor, and no abdominal bruits.
Which of the following plasma values is most likely elevated in this patient?
- A) Direct (unconjugated) bilirubin
- B) Homocysteine
- C) Homovanillic acid
- D) Orexin
- E) 14-3-3 protein
C) Homovanillic acid
This patient is likely presenting with a pheochromocytoma, the most common adult adrenal medullary tumor. Pheochromocytomas secrete the catecholamines dopamine, norepinephrine, and epinephrine, leading to episodically and severely elevated blood pressure. The breakdown products of these substances include metanephrines, vanillylmandelic acid, and homovanillic acid.
Answer choice A: Direct (unconjugated) bilirubin, is incorrect. Direct (unconjugated) bilirubin is a water insoluble heme breakdown product. It is elevated when red blood cell (RBC) destruction exceeds the body’s conjugating capacity, such as in disseminated intravascular coagulation, Crigler-Najjar syndrome, and HELLP syndrome (hemolysis, elevated liver enzymes, low platelets). It would not be expected to increase blood pressure.
Answer choice B: Homocysteine, is incorrect. Homocysteine is an amino acid used in the synthesis of methionine and cystathionine. It is elevated in deficiencies of cystathionine synthase, methionine synthase, and vitamin B6. Patients with these deficiencies are more likely to present with osteoporosis, Marfanoid habitus, lens subluxation, and cardiovascular pathology such as atherosclerosis.
Answer choice D: Orexin, is incorrect. Orexin, also know as hypocretin-1, is secreted by the lateral hypothalamus and is responsible for stimulating and maintaining wakefulness and appetite. A pheochromocytoma would not be expected to elevate orexin.
Answer choice E: 14-3-3 protein, is incorrect. 14-3-3 protein is elevated in the cerebrospinal fluid of patients with Creutzfeld-Jakob disease. These patients typically present with progressive dementia, myoclonus, and ataxia over the course of weeks to months.
Key Learning Point
Pheochromocytomas release catecholamines and typically present with episodic headaches and heart palpitations. Breakdown products include metanephrines, homovanillic acid, and vanillylmandelic acid.