A 55-year-old man comes to the office due to intermittent shortness of breath, cough, and chest tightness over the past 3 months. The patient had asthma as a child that improved in adolescence, and he has not required inhalers or steroids since. He feels that his current symptoms are similar to his prior asthma symptoms. The patient was recently diagnosed with essential tremor, which has improved with medical therapy; he has no other chronic medical conditions. He is a lifetime nonsmoker and does not use alcohol or illicit drugs. Blood pressure is 125/75 mm Hg, pulse is 58/min, and respirations are 16/min. Physical examination reveals bilateral scattered expiratory wheezes. Heart sounds are normal and there is no extremity edema. This patient's symptom recurrence is most likely attributable to a medication that affects which of the following steps?

Question

A 55-year-old man comes to the office due to intermittent shortness of breath, cough, and chest tightness over the past 3 months.  The patient had asthma as a child that improved in adolescence, and he has not required inhalers or steroids since.  He feels that his current symptoms are similar to his prior asthma symptoms.  The patient was recently diagnosed with essential tremor, which has improved with medical therapy; he has no other chronic medical conditions.  He is a lifetime nonsmoker and does not use alcohol or illicit drugs.  Blood pressure is 125/75 mm Hg, pulse is 58/min, and respirations are 16/min.  Physical examination reveals bilateral scattered expiratory wheezes.  Heart sounds are normal and there is no extremity edema.  This patient's symptom recurrence is most likely attributable to a medication that affects which of the following steps?

Quizplus · Accepted Answer

11ec160b_3c0b_7daa_9249_f310703b0579_MD0001_00 This patient has developed symptoms of intermittent asthma (eg, cough, wheeze, dyspnea) associated with a new medication for his essential tremor (ET). ET is a common movement disorder, and beta blockers are often used as first-line therapy for debilitating or distressful symptoms. Beta blockers prevent the interaction of epinephrine and norepinephrine with receptors at adrenergic synapses; in ET, this is thought to help dampen the sensitivity of muscle spindles, which improves tremor symptoms by smoothing out the force of contraction. Propranolol, the most commonly used medication for treatment of ET, is a nonselective beta blocker (ie, inhibits both beta-1 and beta-2 receptors). In patients with reactive airway diseases (eg, asthma, chronic obstructive pulmonary disease), inhibition of beta-2 receptors can cause bronchoconstriction with resultant asthma symptoms. Selective beta-1 blockers are often better tolerated in patients with asthma; however, selectivity is dose-dependent and patients can develop bronchoconstriction at high doses. (Choice A) Tyrosine is transported into the cell by the large neutral amino acid transporter. (Choice B) The conversion of tyrosine to dihydroxyphenylalanine (DOPA) by tyrosine hydroxylase is the rate-limiting step in catecholamine biosynthesis. This enzyme was previously inhibited by drugs used to treat pheochromocytoma, but these are no longer used due to a poor side effect profile. (Choice C) The medication reserpine inhibits vesicular monoamine transporter, thereby inhibiting dopamine entry into presynaptic vesicles and essentially causing a chemical sympathectomy. Reserpine is occasionally used as an antipsychotic. It may cause wheezing in some patients but is not indicated in the treatment of ET. (Choice D) Adrenergic neuron blockers such as guanethidine inhibit norepinephrine release, lowering blood pressure and heart rate. Guanethidine is occasionally used for chronic pain syndrome but does not cause bronchoconstriction; it is not used in management of ET. (Choice E) Tricyclic antidepressants and cocaine work by inhibiting norepinephrine reuptake by presynaptic neurons. These agents can worsen symptoms in ET. Educational objective: Beta blockers are used in the treatment of essential tremor. Propranolol, a nonselective beta blocker, is the most commonly used therapy and prevents the interaction of epinephrine and norepinephrine with beta-1 and beta-2 receptors to relieve tremor symptoms. However, inhibition of pulmonary beta-2 receptors in patients with underlying reactive airway disease can cause bronchoconstriction, leading to cough, wheeze, and dyspnea.

A 55-Year-Old Man Comes to the Office Due to Intermittent