A 45-year-old man comes to the office for evaluation of intermittent episodes of cough and dyspnea for 2 months. The episodes usually occur after exposure to the cold air outside during jogging. The patient gets some relief after expectorating white sputum. Medical history is significant for myasthenia gravis. Four months ago, the patient was intubated for 5 days due to a myasthenic crisis triggered by a viral upper respiratory infection. He takes pyridostigmine and does not use tobacco, alcohol, or illicit drugs. Temperature is 37 C (98.6 F), blood pressure is 128/78 mm Hg, pulse is 78/min, and respirations are 16/min. Pulse oximetry on room air is 98%. Examination shows occasional wheezes on the posterior aspect of both lungs upon forceful exhalation. Heart sounds are normal. Muscle strength is 5/5 in all extremities, cranial nerve function is normal, and deep tendon reflexes are normal. The remainder of the examination shows no abnormalities. Which of the following is the most likely cause of this patient's symptoms?

Question

A 45-year-old man comes to the office for evaluation of intermittent episodes of cough and dyspnea for 2 months.  The episodes usually occur after exposure to the cold air outside during jogging.  The patient gets some relief after expectorating white sputum.  Medical history is significant for myasthenia gravis.  Four months ago, the patient was intubated for 5 days due to a myasthenic crisis triggered by a viral upper respiratory infection.  He takes pyridostigmine and does not use tobacco, alcohol, or illicit drugs.  Temperature is 37 C (98.6 F), blood pressure is 128/78 mm Hg, pulse is 78/min, and respirations are 16/min.  Pulse oximetry on room air is 98%.  Examination shows occasional wheezes on the posterior aspect of both lungs upon forceful exhalation.  Heart sounds are normal.  Muscle strength is 5/5 in all extremities, cranial nerve function is normal, and deep tendon reflexes are normal.  The remainder of the examination shows no abnormalities.  Which of the following is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d4a7_17db_bc81_2deb11a870f6_MD0003_00 This patient who was previously intubated due to a myasthenic crisis now has intermittent episodes of cough and dyspnea. Several features of his presentation suggest intermittent asthma. Important thermomechanical asthma triggers include exercise (eg, jogging) and extremes of temperature and humidity (eg, cold, dry air; hot, humid air). The mechanism likely involves local changes in blood flow and neural input that stimulate inflammatory cell (eg, mast cell, eosinophil) activation and mediator release by leukocytes in the bronchial wall. Key inflammatory mediators include histamine and leukotrienes, which exert paracrine effects on adjacent cells in the airway wall: Smooth muscle cells depolarize, leading to bronchoconstriction. Goblet cells are activated to promote mucus hypersecretion. These responses account for the cardinal symptoms of an asthma attack: episodic dyspnea, cough, and wheezing due to airway inflammation and obstruction. Bronchial edema and hypersecretion may lead to expectoration of nonpurulent (eg, whitish or clear) mucus. Mobilization of these secretions alleviates airway plugging, resulting in partial symptom relief (as seen in this patient). In patients with intermittent asthma, lung sounds may be normal during calm tidal breathing in intermittent asthma, although wheezing can sometimes be elicited by forceful exhalation, reflecting residual airway inflammation and spasticity. Although asthma typically presents in childhood, adult-onset disease is also prevalent and can be triggered by upper respiratory infections (eg, this patient's recent myasthenic crisis), irritants (eg, air pollution), and allergens (eg, mold). (Choice A) Excessive (rather than insufficient) dosage of pyridostigmine, an acetylcholinesterase inhibitor, may cause a cholinergic toxidrome of increased respiratory secretions (ie, bronchorrhea) and bronchospasm. However, gastrointestinal symptoms (eg, nausea, abdominal cramping, secretory diarrhea) usually predominate. (Choice C) Acute hypersensitivity pneumonitis causes non-caseating granulomatous lung disease with subacute episodes of dyspnea in relation to organic antigens (eg, birds, molds). Intermittent and quickly reversible dyspnea and cough with exercise are more suggestive of asthma. (Choice D) Vocal cord dysfunction (ie, paradoxical closure during inspiration) can present with intermittent dyspnea and noisy breathing (ie, inspiratory stridor) triggered by exercise or psychosocial stress. However, it is more common in young women, not typically exacerbated by cold air, and unlikely to cause sputum production. (Choice E) Tracheal stenosis (ie, rigid narrowing) or tracheomalacia (ie, weakness and collapsibility) are complications of prolonged endotracheal intubation, and can cause dyspnea and noisy breathing. Tracheal stenosis is associated with prolonged (>2 weeks) mechanical ventilation, presents with slowly progressive (rather than episodic) dyspnea, and is potentially accompanied by stridor (rather than wheezing). Educational objective: Intermittent asthma is caused by leukocyte-induced acute and reversible bronchoconstriction.

A 45-Year-Old Man Comes to the Office for Evaluation of Intermittent