Asthma differential diagnosis

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Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [1]; Philip Marcus, M.D., M.P.H. [2]

Overview

Asthma must be clinically differentiated from other pulmonary conditions with similar symptoms such as chronic obstructive pulmonary disease and pulmonary aspiration.

Differentiating Asthma from other Diseases

• Before diagnosing someone as asthmatic, alternative possibilities should be considered. A clinician taking a history should check whether the patient is using any known bronchoconstrictors; these substances cause narrowing of the airways, e.g., certain anti-inflammatory agents or beta-blockers and can mimic asthmatic symptoms.
• Chronic obstructive pulmonary disease, which closely resembles asthmatic symptoms, is correlated with:

• More exposure to cigarette smoke
• An older patient
• Less symptom reversibility after bronchodilator administration (as measured by spirometry)
• Decreased likelihood of family history of atopy

• Pulmonary aspiration, whether direct due to dysphagia (swallowing disorder) or indirect (due to acid reflux), can show similar symptoms to asthma. However, with aspiration, fevers might also indicate aspiration pneumonia. Direct aspiration (dysphagia) can be diagnosed by performing a Modified Barium Swallow test and treated with feeding therapy by a qualified speech therapist. If the aspiration is indirect (from acid reflux) then treatment directed at this is indicated.
• A majority of children who are asthma sufferers have an identifiable allergy trigger. Specifically, in a 2004 study, 71% had positive test results for more than 1 allergen, and 42% had positive test results for more than 3 allergens.
• The majority of these triggers can often be identified from the history; for instance, asthmatics with hay fever or pollen allergy will have seasonal symptoms, those with allergies to pets may experience an abatement of symptoms when away from home, and those with occupational asthma may improve during leave from work. Occasionally, allergy tests are warranted and, if positive, may help in identifying avoidable symptom triggers.
• After a pulmonary function test has been carried out, radiological tests, such as a chest X-ray or CT scan, may be required to exclude the possibility of other lung diseases.
• In some people, asthma may be triggered by gastroesophageal reflux disease, which can be treated with suitable antacids. Very occasionally, specialized tests after inhalation of methacholine — or, even less commonly, histamine — may be performed.
• Asthma is categorized by the United States National Heart, Lung and Blood Institute as falling into one of four categories:

• Intermittent
• Mild persistent
• Moderate persistent
• Severe persistent

• The diagnosis of "severe persistent asthma" occurs when symptoms are continual with frequent exacerbations and frequent nighttime symptoms, result in limited physical activity and when lung function as measured by PEV or FEV₁ tests is less than 60% predicted with PEF variability greater than 30%.