Step-by-step diagnostic approach of dyspnea.Clinical historyCareful history-taking is the most useful first step in elucidating the aetiology of dyspnoea. Several factors need to be addressed in the clinical history when constructing the initial differential diagnosis. Time course Acute dyspnoea appears suddenly or in a matter of minutes. It typically indicates acute and severe conditions that may be life-threatening. Examples of conditions causing sudden-onset dyspnoea include acute pulmonary embolism, myocardial infarction, acute heart valve insufficiency, pneumothorax, anaphylaxis, foreign body aspiration, pulmonary oedema, or cardiac tamponade. 16 Subacute dyspnoea develops over hours to days. Common causes include acute asthma, exacerbation of COPD, or pulmonary oedema. Less common causes include myocarditis, superior vena cava syndrome, acute eosinophilic pneumonia, or cardiac tamponade. 16 17 18 Chronic dyspnoea develops over weeks to months. It is associated with chronic pathology, such as congestive heart failure, COPD, cardiomyopathy, idiopathic pulmonary fibrosis, pulmonary vascular disease, pulmonary hypertension, valvular heart disease, or anaemia. 19 Less common causes include muscular dystrophies, kyphoscoliosis, amyotrophic lateral sclerosis, pulmonary alveolar proteinosis, chronic eosinophilic pneumonia, uraemia, or constrictive pericarditis. 18 20 21 22 23 Recurrent dyspnoea may indicate paroxysmal tachycardias or intermittent complete heart block.Severity There is no universally agreed measure of dyspnoea; several scales are available in both research and clinical practice. 24 Dyspnoea is highly subjective, and, for a given level of functional impairment, severity varies widely. Severe dyspnoea is typically accompanied by associated symptoms and is more likely to be life-threatening. It may be associated with acute asthma, tension pneumothorax, acute upper airway obstruction, massive pulmonary embolism, or myocardial infarction. Mild dyspnoea may be a sole symptom and may indicate a benign aetiology. It may be caused by stable COPD, deconditioning, non-critical airway obstruction, or normal ageing. Associated symptoms Dyspnoea often occurs with other symptoms, and their co-existence may help to localise the origin of dyspnoea to the involved organ system and help to narrow the differential diagnosis. Fever manifests with dyspnoea in many infectious and inflammatory conditions, including pneumonia, bronchitis, laryngitis, viral syndromes (e.g., Hantavirus pulmonary syndrome and severe acute respiratory syndrome SARS), vasculitides, and sepsis. 25 26 Dyspnoea plus fever and cough may indicate community-acquired pneumonia or opportunistic infection in immunocompromised hosts. A CXR is necessary to exclude pneumonia. Post-obstructive pneumonia is possible in patients with foreign body aspiration or a chest malignancy. Central chest pain may suggest coronary artery disease, pulmonary embolism, pneumothorax, pneumomediastinum, or foreign body aspiration. 27 Pleuritic chest pain may indicate pneumonia, pneumothorax, pulmonary embolism, a solitary fibrous tumour of the pleura, or pleuritis. 28 Pericardial constriction and effusions are characterised by typical pericardial pain that is referred to the scapular region, worsened by position and changes in intrathoracic pressure, and relieved by leaning forwards. Palpitations may be present in paroxysmal tachyarrhythmias, pulmonary embolism, valvular heart disease, or anxiety attacks. Syncope may accompany dyspnoea associated with tachyarrhythmias or pulmonary embolism. 29 Wheezing may indicate asthma, COPD, pulmonary oedema, bronchiolitis, or aspiration of a foreign body. Cough may be present in bronchitis, acute infectious pneumonia, acute eosinophilic pneumonia, interstitial lung disease, COPD, asthma, bronchiectasis, or chronic pneumonitis. 18 Chronic sputum production may indicate COPD or bronchiectasis, while large amounts of clear secretions may be present in bronchoalveolar carcinoma. 30 Change in the pitch of the voice may accompany dyspnoea associated with pneumomediastinum, gastro-oesophageal reflux, retropharyngeal haematoma, aortic aneurysm, or lung cancer. 31 Haemoptysis may accompany dyspnoea in patients with bronchitis, exacerbation of bronchiectasis, chest malignancies, vasculitides, acute infectious pneumonia, cryptogenic organising pneumonia, pulmonary embolism, cocaine toxicity, tuberculosis, or diffuse alveolar haemorrhage. 32 33 34 35 36 37 Dysphagia or odynophagia may be present in a dyspnoeic patient with granulomatous laryngitis, pneumomediastinum, foreign body aspiration, tetanus, and epiglottitis. 38 39 40 In epiglottitis, dyspnoea may be additionally accompanied by drooling. Vomiting and diarrhoea may accompany dyspnoea in thyrotoxicosis or botulism. 41 42 Heartburn may be present in gastro-oesop