Differentials
Aspiration pneumonitis
SIGNS / SYMPTOMS
Results from aspiration of sterile gastric contents (often witnessed), leading to acute lung injury from acidic and particulate gastric material.
Occurs immediately after the precipitating event.
Typically occurs in young people, and the main risk factor is a markedly depressed level of consciousness.[8]
Clinically difficult to distinguish. Symptoms persist beyond the initial 24 hours. Similar pulmonary signs are seen such as coughing, wheezing, cyanosis, hypoxemia, pulmonary edema, respiratory distress, or gastric contents in oropharynx.
Cardiac signs such as hypotension are also similar.
INVESTIGATIONS
There is no good test. Clinical history can help to differentiate.[8]
Atelectasis
SIGNS / SYMPTOMS
Depends on the size of area of lung affected and speed at which lung collapse occurs. If a large area of the lung is affected with rapid onset, there is typically pain on the affected side, dyspnea (sudden onset), and cyanosis. Slower onset of lung collapse may be asymptomatic or cause only minor symptoms. A harsh, nonproductive cough is produced by gradual collapse of the right middle and lower lobes.
INVESTIGATIONS
Lack of leukocytosis or other markers of active infection. CXR usually shows changes in posterior dependent aspects.
Pulmonary edema
SIGNS / SYMPTOMS
Presents with shortness of breath, fatigue, dyspnea on exertion, and tachypnea. History of heart disease or fluid overload can usually be elicited.
Crackles are heard on auscultation.
INVESTIGATIONS
CXR typically shows symmetric distribution of opacities, although may not be evident early on. Evaluation of left ventricular dysfunction by BNP and echo are helpful.
Leukocytosis usually not present.
Lipoid pneumonia
SIGNS / SYMPTOMS
Form of aspiration pneumonia occurring acutely or chronically from aspiration of vegetable fat or mineral oil (exogenous form). There is a history of ingestion of lipid over periods of time. Acute form may present with fever and cough especially in younger patients. Chronic form may be asymptomatic.
Can be seen resulting from propylene glycol in electronic cigarettes and other vaporizers.
INVESTIGATIONS
CT can occasionally demonstrate low attenuation areas (-30HU).
Community-acquired pneumonia (CAP)
SIGNS / SYMPTOMS
Patients typically complain of productive cough, breathlessness, chest or abdominal pain, fever, and general malaise. Older people present with atypical symptoms including confusion, lethargy, and general deterioration.
It is possible that aspiration pneumonia is simply community-acquired pneumonia in an older patient with greater comorbidities.[4]
INVESTIGATIONS
Common organisms detected on sputum culture are Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Moraxella catarrhalis, Klebsiella pneumoniae, and other gram-negative bacilli.
Atypical organisms may be detected with appropriate testing (e.g., serology or antigen tests).
Hospital-acquired pneumonia (HAP)
SIGNS / SYMPTOMS
Green-yellow sputum.
No difference in signs and symptoms. HAP refers to any pneumonia that develops after 72 hours of hospitalization. This includes all types of pneumonias, including aspiration pneumonia.
INVESTIGATIONS
Sputum culture showing growth of gram-negative rods or Staphylococcus aureus is more likely.
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