Differential Diagnosis for Asthma

1.Cystic fibrosis

Differential symptoms/signs:

Chronic, sometimes productive cough with a possible family history of CF. Nasal polyposis at or before age 12 and symptoms related to other organ involvement, such as diarrhoea, malabsorption or failure to thrive.

Test:

Sweat chloride testing: level of sweat chloride >67.

Consider repeat testing.

2.Tracheomalacia

Differential signs/symptoms:

Symptoms are usually positionally dependent and occur within the first weeks or months of life.

Expiratory stridor and a barking brassy cough, wheezing respiratory distress with additional breath sound at the end of expiration (the bagpipe sign) are accompanied by the occasional extension of the neck with breathing, inspiratory stridor, episodes of holding of breath, anoxia, recurrent respiratory infections, retraction of intercostal and subcostal muscles, failure to thrive and respiratory and cardiac arrest.

Test:

The sensitivity of plain radiographs is 62%, using microlaryngoscopy and bronchoscopy as the reference standards.

In addition to CXR, barium oesophagography is useful for evaluating associated disease processes, such as tracheo-oesophageal fistula and reflux disease.

3.Vascular ring

Differential signs/symptoms:

Wheezing, shortness of breath, occasional stridor.

Test:

CT chest with contrast: double aortic arch, abnormal take-off of the innominate artery, anomaly of left pulmonary artery, right aortic arch, aberrant right subclavian, enlarged pulmonary veins.

4.Foreign body aspiration

Differential signs/symptoms:

Wheezing, shortness of breath, occasional stridor are common.

If the foreign body is in the peripheral airway, localised one-sided wheezing or collapse of the distal lung tissue is found.

Test:

CXR, CT chest or bronchoscopy shows the foreign body.

5.Vocal cord dysfunction

Differential Signs/symptoms:

Inspiratory and expiratory wheezing is often difficult to differentiate. Should be considered in steroid-resistant asthma patients.

Test:
Direct visualisation of the vocal cords with rhinolaryngoscopy during a spell. Inspiratory flow volume loop is helpful when abnormal (flattened).

6.Alpha-1 antitrypsin deficiency

Differential signs/symptoms:

Wheezing, resistant to management. May have family history of parents or grandparents dying of lung disease.

Test:
Testing for the alpha-1 antitrypsin phenotype.

7.COPD

Differential signs/symptoms:

Dyspnoea occurs with or without wheezing and coughing.

Examination may show barrel chest, hyper-resonance to percussion and distant breath sounds.

Test:
PFTs with residual volume (RV), total lung capacity (TLC) and a flow volume loop with bronchodilator showing an obstructive pattern with an increase in TLC and RV and a reduction in forced expiratory flow at one second (FEV1), FEV1/forced vital capacity (FVC) ratio with no response to bronchodilator.

CXR showing hyper-inflation of the lungs.

8.Bronchiectasis

Differential signs/symptoms:

Dyspnoea, cough and wheezing and, if severe, recurrent pulmonary infections.

Test:
High resolution CT chest: dilated airways, bronchial wall thickening.

Can occasionally be seen on CXR.

9.Pulmonary embolism

Differential signs/symptoms:

Patients have a wide variety of presentations but most common is shortness of breath and pleuritic pain.

Test:
Pulmonary angiogram is the preferred test, but carries risks. An acceptable alternate test is CT angiogram of the lung, which, if not available, can be replaced with the less sensitive V/Q scan.

10.Congestive heart failure

Differential signs/symptoms:

History of CAD or uncontrolled HTN; examination showing dependent oedema, elevated jugular venous pressure, and basal pulmonary crepitations.

Test:
CXR may show increased alveolar markings, fluid in fissures and pleural effusions.

Echocardiogram: reduced left ventricular ejection fraction.

11.Common variable immunodeficiency

Differential sign/symptoms:

History of recurrent, usually sinopulmonary, infections.

Test:
Serum IgG level below 5g/L (500 mg/dL).