17th January 2024

Differential diagnoses

Pulmonary oedema

Cardiogenic pulmonary oedema is the most important differential for ARDS, and when severe, can have an almost identical appearance on chest x-ray. Whilst both can be associated with progressive shortness of breath and worsening oxygen requirement, certain signs on examination can help differentiate the two. A raised JVP, presence of a third heart sound and peripheral oedema are all present in pulmonary oedema but not in ARDS. There also may be clues in the history, such as a recent acute coronary syndrome or known pre-existing valvular disease. It is important to distinguish the two, as pulmonary oedema can respond well to the timely initiation of IV diuretics.

Pulmonary haemorrhage

Diffuse alveolar haemorrhage can have a similar radiological appearance to ARDS. Clinically, remain clinically suspicious of pulmonary haemorrhage with any patient presenting with haemoptysis or a very acute onset breathlessness.

Pulmonary vasculitis

Conditions such as granulomatosis with polyangiitis (GPA) and eosinophilic granulomatosis with polyangiitis (EGPA) can present with bilateral infiltrates on chest x-ray and a similar symptom profile to ARDS. However, patients can also have evidence of multi-system involvement, such as vasculitic skin rash and renal impairment. Differentiate this patient group by sending off an autoimmune screen, including ANA, ANCA and double-stranded DNA (dsDNA).

Lymphangitic carcinomatosis

In patients with disseminated malignancy presenting with unexplained worsening shortness of breath and dry cough suspect pulmonary lymphangitis, where the lymphatic channels in the lungs are infiltrated by malignant cells. Presentation is often too indolent here to meet the diagnostic criteria for ARDS (3).