Patient Presentation: BE is a 45-year-old woman who presents with concerns about sudden (paroxysmal), intense, brief episodes of headache, sweating (diaphoresis), and a racing heart (palpitations).
Focused History: BE reports that the attacks started ~3 weeks ago. They last from 2 to 10 minutes, during which time she feels quite anxious. During the attacks, it feels as though her heart is skipping beats (arrhythmia). At first, she thought the attacks were related to recent stress at work and maybe even menopause. The last time it happened, she was in a pharmacy and had her blood pressure taken. She was told it was 165/110 mm Hg. BE notes that she has lost weight (~8 lbs) in this period even though her appetite has been good.
Pertinent Findings: The physical examination was remarkable for BE’s thin, pale appearance. Blood pressure was elevated (150/100 mm Hg), as was the heart rate (110–120 beats/minute). Based on BE’s history, blood levels of normetanephrine and metanephrine were ordered. They were found to be elevated.
Diagnosis: BE has a pheochromocytoma, a rare catecholamine-secreting tumor of the adrenal medulla.
Treatment: Imaging studies of the abdomen were done to locate the tumor. Surgical resection of the tumor was performed. The tumor was found to be nonmalignant. Follow-up measurement of plasma metanephrines was performed 2 weeks later and was in the normal range.
Prognosis: The 5-year survival rate for nonmalignant pheochromocytomas is >95%.
Case-Related Questions: Choose the ONE best answer.
Q1. Pheochromocytomas secrete norepinephrine (NE) and epinephrine. Which of the following statements concerning the synthesis and degradation of these two biogenic amines is correct?
A. The substrate for their synthesis is tryptophan, which is hydroxylated to 3,4-dihydroxyphenylalanine (DOPA) by tetrahydrobiopterin-requiring tryptophan hydroxylase.
B. The conversion of DOPA to dopamine utilizes a pyridoxal phosphate– requiring carboxylase.
C. The conversion of NE to epinephrine requires vitamin C.
D. Degradation involves methylation by catechol-O-methyltransferase and produces normetanephrine from NE and metanephrine from epinephrine.
E. Normetanephrine and metanephrine are oxidatively deaminated to homovanillic acid by monoamine oxidase.
Q2. Which of the following statements concerning the actions of epinephrine and/or NE are correct?
A. NE functions as a neurotransmitter and a hormone.
B. They are initiated by autophosphorylation of select tyrosine residues in their receptors.
C. They are mediated by binding to adrenergic receptors, which are a class of nuclear receptors.
D. They result in the activation of glycogen and triacylglycerol synthesis.
Q3. NE bound to certain receptors causes vasoconstriction and an increase in blood pressure. Why might NE be used clinically in the treatment of septic shock?
Case 5: Sun Sensitivity
Patient Presentation: AZ is a 6-year-old boy who is being evaluated for freckle-like areas of hyperpigmentation on his face, neck, forearms, and lower legs.
Focused History: AZ’s father reports that the boy has always been quite sensitive to the sun. His skin turns red (erythema) and his eyes hurt (photophobia) if he is exposed to the sun for any period of time.