Differentials
Work-exacerbated asthma
SIGNS / SYMPTOMS
Nonspecific worsening of preexisting or coincidental asthma due to workplace irritants such as dust and fumes, or common allergens that may be present in the workplace.[70]
Usually a history of preceding asthma before current employment, which is associated with worsening asthma symptoms.
INVESTIGATIONS
Negative specific inhalation challenge (when the correct agent is identified) and lack of change in serial nonspecific bronchial hyper-responsiveness (NSBHR) testing are suggestive of work-exacerbated asthma.
However, lack of change in airway responsiveness away from the suspected work agent does not exclude occupational asthma (OA). Advanced or longstanding sensitizer-induced OA may be associated with less temporal variability in symptoms and lung function with workplace exposure.
Occupational eosinophilic bronchitis
Coincidental nonoccupational asthma
SIGNS / SYMPTOMS
Asthma is a common condition that frequently will present initially, or recur in adult life.
The clinician should take a history of the home environment to identify other potential allergens such as cats or dust. Unrelated asthma should be considered if no features of irritant-induced occupational asthma (OA), a workplace sensitizer, or objective evidence of worsening at the workplace to suggest sensitizer-induced OA are identified.[38][86]
INVESTIGATIONS
Clinical diagnosis: lack of features to suggest irritant-induced OA, or lack of changes in symptoms, treatment needs, pulmonary function, or bronchial hyper-responsiveness associated with workplace exposures that suggest sensitizer-induced OA make the presence of nonoccupational asthma more likely.
Hypersensitivity pneumonitis
SIGNS / SYMPTOMS
Many substances that cause occupational asthma may also cause hypersensitivity pneumonitis (HP), including diisocyanate exposure.
In HP, wheezing does not tend to be a prominent feature, and patients with the acute form may experience fevers and chills.
INVESTIGATIONS
Absence of (or mild) nonspecific bronchial hyper-responsiveness (NSBHR).
Other pulmonary function abnormalities associated with HP include a restrictive ventilatory defect and impairment in gas transfer.
Chest x-ray shows patchy, nodular infiltrates in acute and subacute HP; fibrosis in chronic HP.
High-resolution CT chest in chronic HP shows ground-glass shadowing/attenuation and poorly defined micronodules. There is extensive honeycombing in late stages.
Chronic bronchitis/COPD
SIGNS / SYMPTOMS
Dyspnea may occur with or without wheezing, cough, or sputum. Examination may show barrel chest, hyper-resonance to percussion, and distant breath sounds.
It is estimated that approximately 15% of COPD may be work-related from exposure to factors such as mineral and organic dusts.[87] COPD should especially be considered if there is a history of tobacco use and less day-to-day variability in symptoms.
INVESTIGATIONS
Lack of significant variability in airflow obstruction and an absence of, or only mild, nonspecific bronchial hyper-responsiveness (NSBHR; although COPD and asthma may coexist).
Vocal cord dysfunction
SIGNS / SYMPTOMS
Upper airway disorders commonly mimic asthma.[88]
Asthma may be present in addition to vocal cord dysfunction.
INVESTIGATIONS
Pulmonary function testing may suggest extrathoracic airflow limitation caused by paradoxical vocal cord movement by the presence of a flattened inspiratory flow volume loop.[89]
Lack of objective airflow obstruction or nonspecific bronchial hyper-responsiveness (NSBHR) is supportive of the diagnosis; however, assessment by an otolaryngologist and speech therapist experienced in the field is recommended.[88]
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