A 38-year-old man is being evaluated due to shortness of breath, cough, and chest tightness. He reports that his breathing "gets noisy" sometimes. The symptoms appeared 3 months ago, last throughout most of the day, and have gradually become more severe. The patient started working as a research laboratory technician 2 years ago, spending most of his day maintaining rodent colonies. He is unsure whether the respiratory symptoms are related to his arrival at or departure from the animal facility. The patient's breathing improved when he attended a weeklong conference in another city. He reports no fevers, night sweats, weight loss, or unusual fatigue. Vital signs are within normal limits. Nasal and pharyngeal mucosae are normal. Pulmonary examination shows normal lung sounds. Chest x-ray is normal. Baseline spirometry demonstrates mild airflow obstruction that is reversed after the administration of albuterol. Which of the following diagnostic tests will be most useful for establishing the diagnosis?
Occupational asthma | |
Pathogenesis |
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Clinical |
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Management |
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BHR = bronchial hyperresponsiveness; PEFR = peak expiratory flow rate. | |
This patient has respiratory symptoms and reversible airflow obstruction on spirometry at baseline, findings consistent with asthma. Symptoms improve on sustained absence from the workplace (ie, weeklong conference). This key history element is suggestive of occupational asthma, defined as asthma specifically driven by workplace antigen exposure.
Classic occupational antigens include animal proteins (eg, laboratory rodent workers), isocyanates (eg, painters), and metals (eg, welders). Because of the long latency period required for immune sensitization, occupational asthma may not manifest for months to years. Initially, patients may link symptoms closely to the workplace. Eventually, when airway inflammation becomes established, symptoms may persist even at home throughout the week and subside only after prolonged absence (eg, vacations).
Therefore, diagnosis requires a detailed occupational history, careful symptom timeline, and 2-step confirmatory testing:
First, asthma must be confirmed (eg, reversible obstruction on spirometry). For patients with normal baseline spirometry, bronchoprovocation (eg, methacholine) is performed to confirm bronchial hyperresponsiveness.
Next, an occupational relationship is established by confirming workplace-specific worsening of airflow obstruction (Choice C). This can be accomplished with serial peak expiratory flow rate (PEFR) measurements using a portable peak flow meter.
Patients record their PEFR at home and at work (along with their symptoms): a PEFR decline by ≥20% at the workplace relative to at home is consistent with occupational asthma.
(Choice A) Occupational hypersensitivity pneumonitis can present with respiratory symptoms waxing and waning with workplace exposure. However, chest CT demonstrates ground-glass opacities (reflecting alveolitis), spirometry shows restriction or a mixed pattern, and constitutional symptoms are common.
(Choice B) Vocal cord dysfunction (ie, paradoxic inspiratory adduction) can present with dyspnea and noisy breathing (stridor). However, it tends to affect young women, attacks occur in discrete episodes (instead of lasting the day), and spirometric flow-volume loop abnormalities would be expected.
(Choice E) Occupational allergic rhinitis can be relieved with intranasal steroids. The condition can cause postnasal drip, producing chronic cough with no obvious physiologic abnormalities. However, nasal and sinus symptoms would be expected, and signs of upper airway allergy would be seen on physical examination (eg, turbinate hypertrophy, pharyngeal cobblestoning).
Educational objective:
Occupational asthma is induced by workplace antigen exposure (eg, animal proteins, isocyanates). Chronic occupational asthma may produce persistent airway inflammation and bronchoconstriction that subside only after prolonged absence from work. Once asthma is diagnosed (eg, baseline spirometry), occupational asthma is confirmed by demonstrating workplace-specific worsening of airflow obstruction (eg, fall in peak expiratory flow).