Can pulmonary embolism cause fever?

Can Pulmonary Embolism Cause Fever?

Yes, pulmonary embolism can cause fever, occurring in approximately 14-26% of patients with PE who have no other identifiable source of infection. 1, 2

Pathophysiological Mechanisms

The European Society of Cardiology explains that fever in PE results from an inflammatory response triggered by thromboemboli in the pulmonary vasculature, with massive inflammatory cell infiltrates found in the right ventricular myocardium of patients who died within 48 hours of acute PE. 3

• PE-induced "myocarditis" may develop from high epinephrine levels released during neurohumoral activation in response to right ventricular wall tension and circulatory shock. 3
• The inflammatory cascade can explain secondary hemodynamic destabilization that sometimes occurs 24-48 hours after the acute PE event. 3
• Distal emboli cause alveolar hemorrhage leading to pleural irritation, even when these emboli don't significantly affect hemodynamics—this presents clinically as "pulmonary infarction" though true histopathological infarction is uncommon. 4

Clinical Characteristics of PE-Related Fever

Low-grade fever is the most common pattern, but high-grade fever can occur and should not exclude PE from your differential diagnosis. 1, 5

• Among 311 patients with angiographically proven PE and no other fever source, 14% developed fever. 1
• A more recent study found fever in 25.7% of hospitalized PE patients after excluding those with concurrent infections. 2
• Fever occurs with equal frequency regardless of whether pulmonary hemorrhage or infarction is present (15% vs 9%, not statistically significant). 1
• Clinical evidence of deep venous thrombosis is often present in patients with PE and otherwise unexplained fever. 1

Fever Patterns and Duration

High fever (>39°C) can occur early in the PE course, and low-grade fever may persist for a week or more. 5

• Critical caveat: Fever persisting beyond 6 days, especially with temperatures >38.5°C, should prompt careful exclusion of other causes before attributing it solely to PE. 5
• However, if the clinical setting and findings are consistent with PE, do not be deterred from making the diagnosis and initiating anticoagulation solely because of high fever. 5

Clinical Implications and Prognostic Significance

Patients with PE and fever have significantly worse outcomes compared to those without fever. 2

• PE patients with fever are more likely to require ICU admission (69.5% vs 35.7%, p<0.001). 2
• They have longer hospital length of stay (19.8 vs 12.2 days, p<0.001). 2
• Higher requirement for mechanical ventilation (30.5% vs 6.6%, p<0.001). 2
• Greater clot burden: More likely to have massive or submassive PE (55.9% vs 36.8%, p=0.015). 2
• Higher incidence of concurrent DVT (33.3% vs 17.4%, p=0.0347). 2
• Increased in-hospital mortality (22.0% vs 10.4%, p=0.039). 2

Critical Diagnostic Pitfalls

Pneumonia frequently masks PE due to considerable overlap in clinical presentation, particularly when systemic symptoms like fever predominate. 6

• Case reports document patients initially diagnosed and treated for pneumonia who showed initial improvement with antibiotics, only to worsen during treatment—ultimately diagnosed with PE on CT pulmonary angiography. 6
• Always consider PE in pneumonia patients who show initial therapeutic response followed by clinical deterioration, especially with persistent pleuritic chest pain, hemoptysis, or breathlessness. 6
• High-grade fever responsive to anticoagulation alone (without antibiotics) has been documented in saddle PE, with defervescence occurring 3 days after anticoagulation initiation. 7

Practical Clinical Approach

Include PE in your differential diagnosis for any patient with unexplained fever, particularly when:

• Risk factors for VTE are present (immobility, malignancy, recent surgery, DVT signs). 1, 2
• Fever is accompanied by pleuritic chest pain, dyspnea, or hemoptysis. 6
• Younger patients with smoking history present with fever (PE with fever patients tend to be younger). 2
• Fever persists despite appropriate antibiotic therapy for presumed infection. 6, 7

Do not exclude PE from consideration based solely on the presence of high fever—proceed with appropriate risk stratification using Wells or Geneva scores and pursue imaging as indicated. 5