Differentials
Coronavirus disease 2019 (COVID-19)
SIGNS / SYMPTOMS
Important to consider the current COVID-19 epidemiologic situation and any recent outbreaks. May give history of COVID-19 exposure or unwell contacts.
Differentiating bacterial pneumonia from COVID-19 is not usually possible from signs and symptoms. However, patients with COVID-19 are less likely to have rapid development of symptoms and a productive cough with purulent sputum. They are more likely to have myalgia or pleuritic pain.[63] The presence of anosmia or ageusia (loss of smell or taste) may be useful as a red flag for the presence of COVID‐19.[64]
INVESTIGATIONS
Real-time reverse transcription polymerase chain reaction (RT-PCR): positive for SARS-CoV-2 RNA. Rapid antigen tests may also be used.
Chest imaging alone is unreliable in differentiating COVID-19 from other causes of pneumonia due to the inconsistency with which COVID-19 results in imaging findings. No single feature on chest x-ray is considered diagnostic for COVID-19. Imaging may be used to support the diagnosis, especially in cases where suspicion is high but other diagnostic testing has come back negative for COVID-19. The most common findings are ground-glass opacities and/or consolidation, with distribution commonly being bilateral and peripheral with basal zone predominance. Pleural effusion, cavitations, and pneumothorax are rarely seen.[65]
Cardiogenic pulmonary edema
SIGNS / SYMPTOMS
Heart failure symptoms include dyspnea, jugular venous distention, an S3 gallop, and edema.
The concomitant presentation of HAP with an effusion or edema 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, myocardial infarction, ischemia, or ventricular hypertrophy.
Echocardiography can be diagnostic. B-type natriuretic peptide may be elevated.
Acute respiratory distress syndrome
SIGNS / SYMPTOMS
Dyspnea and tachypnea are common before intubation. If acute respiratory distress syndrome (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 generalized 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 shortness of breath, possible hypoxia, and hypocapnia.
INVESTIGATIONS
Computed tomographic pulmonary angiography (CTPA) will show direct visualization of thrombus in a pulmonary artery.
Elevation of D-dimer (may also be raised in pneumonia).[66]
ECG may show evidence of right ventricular dysfunction; however, ECG cannot definitively establish or eliminate pulmonary embolism as a diagnosis.[67][68][69]
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 hemorrhage
SIGNS / SYMPTOMS
Hemoptysis with acute hemodynamic instability. Other nonspecific pulmonary symptoms include cough, dyspnea, and chest pain.
There may be a history of Goodpasture syndrome.
INVESTIGATIONS
Chest x-ray would show diffuse alveolar filling in a perihilar or basilar distribution. However, this is difficult to distinguish from pulmonary edema or a diffuse infectious process. A CT would better differentiate between infiltrate and fluid. Patient may be anemic.
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).
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