Differentials
Coronavirus disease 2019 (COVID-19)
SIGNS / SYMPTOMS
Residence in/travel history to an area with ongoing transmission, or close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.
Differentiating bacterial pneumonia from COVID-19 is not usually possible from signs and symptoms. However, patients with bacterial pneumonia are more likely to have rapid development of symptoms and purulent sputum. They are less likely to have myalgia, anosmia, or pleuritic pain.[39]
Bacterial co-infection occurs in less than 8% of patients with COVID-19, and infection rates may be lower in people in hospital with COVID-19. The risk of hospital-acquired pneumonia increases with length of hospital stay and with immunosuppression.[45]
This topic covers pneumonia caused by COVID-19 as a differential diagnosis only. For more detail on the diagnosis and management of hospital-acquired pneumonia caused by COVID-19, seeCoronavirus disease 2019 (COVID-19).
INVESTIGATIONS
Real-time reverse transcription polymerase chain reaction (RT-PCR): positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA.
It is not possible to differentiate COVID-19 from other causes of pneumonia on chest imaging.
Cardiogenic pulmonary oedema
SIGNS / SYMPTOMS
Heart failure symptoms include dyspnoea, jugular venous distension, an S3 gallop, and oedema.
The concomitant presentation of HAP with an effusion or oedema makes diagnosis complicated.
INVESTIGATIONS
Chest x-ray may show cardiomegaly, upper lobe diversion, fluid in the fissures, pleural effusion, and diffuse interstitial or alveolar shadowing.
ECG may give clues as to the cause: for example, MI, ischaemia, or ventricular hypertrophy.
Echocardiography can be diagnostic. B-type natriuretic peptide (BNP) may be elevated.
ARDS
SIGNS / SYMPTOMS
Dyspnoea and tachypnoea are common before intubation. If ARDS is secondary to an infection, a fever will be present. Furthermore, fever is a feature of fibroproliferative ARDS.
INVESTIGATIONS
The ratio of FiO2 to PaO2 <200 supports ARDS in the context of a diffuse opacity.
Patients are typically intubated and sedated and therefore a common method of diagnosis is generalised pulmonary opacity seen on chest x-ray.
Pleural effusion
SIGNS / SYMPTOMS
Cough may be severe; pleurisy may be present.
INVESTIGATIONS
A CT scan distinguishes fluid from atelectatic lung because the fluid is confined to the compartment of the pleural space, typically creating a well-defined line on imaging.
Pulmonary embolus
SIGNS / SYMPTOMS
More-acute onset of SOB, possible hypoxia, and hypocapnia.
INVESTIGATIONS
Spiral CT scan positive; newer scans are better at detecting peripheral emboli.
Atelectasis
SIGNS / SYMPTOMS
Usually not hypoxic or febrile, although a low-grade fever may be present.
INVESTIGATIONS
Leukocytosis and sputum production may or may not be present.
Opacities on a chest x-ray tend to be more linear than lobar shaped.
Pulmonary haemorrhage
SIGNS / SYMPTOMS
Haemoptysis with acute haemodynamic instability. Other non-specific pulmonary symptoms include cough, dyspnoea, and chest pain.
There may be a history of Goodpasture's syndrome.
INVESTIGATIONS
Chest x-ray would show diffuse alveolar filling in a perihilar or basilar distribution. However, this is difficult to distinguish from pulmonary oedema or a diffuse infectious process. A CT would better differentiate between infiltrate and fluid. Patient may be anaemic.
Lung cancer
SIGNS / SYMPTOMS
Similar symptoms, but differentiating factor is that symptoms may have been present for many weeks.
INVESTIGATIONS
A CT scan would be more likely to show neoplasm as a different morphology (nodular) with possible metastatic involvement of other tissue (bone).
Aspiration pneumonia
SIGNS / SYMPTOMS
No difference in signs and symptoms. More common in older people in hospitals and nursing homes, especially those with dysphagia, impaired mental status, neurological diseases (including cognitive impairment), or mechanical impairment of the digestive tract.
INVESTIGATIONS
Sputum or tracheal Gram stain reveals mixed flora.
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