What does a pleural friction rub that intensifies with deep inspiration indicate, and how should it be evaluated and managed?

Pleural Friction Rub with Deep Inspiration

A pleural friction rub that intensifies with deep inspiration indicates pleural inflammation (pleuritis) and requires immediate evaluation to exclude life-threatening causes—particularly pulmonary embolism, pneumonia with pleural involvement, and pericarditis—before attributing it to benign self-limited viral pleurisy. 1

What a Pleural Friction Rub Indicates

• A pleural friction rub is a coarse, grating, creaking sound—often described as "walking on fresh snow" or "creaking leather"—that occurs when inflamed visceral and parietal pleural surfaces rub against each other during respiration. 1

• The rub is characteristically biphasic (heard during both inspiration and expiration), does not clear with coughing, and is typically louder and more prominent than crackles. 1

• Deep inspiration accentuates the rub because greater lung expansion increases the surface area of contact between the inflamed pleural layers and amplifies the friction. 1

• The presence of a friction rub confirms pleural inflammation but does not distinguish between infectious, embolic, malignant, or autoimmune etiologies—all of which require different management. 1

Life-Threatening Causes to Exclude First

Pulmonary Embolism (PE)

• Pulmonary embolism commonly presents with pleuritic chest pain (in ~52% of cases) due to distal emboli causing alveolar hemorrhage and pleural irritation; a friction rub may develop when infarction extends to the pleural surface. 1

• Sudden dyspnea with pleuritic pain that worsens on inspiration, tachycardia (>90% of PE patients), and tachypnea (~70%) are the hallmark features. 1, 2

• Apply the Wells criteria to estimate pre-test probability; obtain an age- and sex-adjusted D-dimer for low-to-intermediate probability, or proceed directly to CT pulmonary angiography if clinical suspicion is high. 1

• A pleural effusion develops in approximately 46% of PE cases and is frequently hemorrhagic, contributing to ongoing pleuritic discomfort and potentially masking the friction rub on examination. 1

Pneumonia with Pleural Involvement

• Pneumonia may present with localized pleuritic pain and a friction rub when the inflammatory process extends to the visceral pleura. 1

• Key distinguishing features include fever, productive cough, crackles on auscultation, and consolidation on chest radiograph. 2

• Empyema occurs in up to 10% of patients with bacteremic pneumococcal pneumonia and requires urgent evaluation with repeat chest radiograph, CT scan if pleural fluid is suspected, and sampling/culture of any pleural fluid. 1

Pericarditis

• Acute pericarditis produces sharp, pleuritic chest pain that improves when sitting forward and worsens when lying supine—a pathognomonic feature that helps distinguish it from pure pleural disease. 1, 2

• A pericardial friction rub may be audible (though its absence does not exclude pericarditis), and the ECG typically shows diffuse concave ST-segment elevation with PR-segment depression. 1, 2

• Bedside transthoracic echocardiography should be performed immediately to identify pericardial effusion (present in ~60% of acute pericarditis cases) and assess for tamponade physiology. 2

Diagnostic Evaluation Algorithm

Immediate Assessment (First 10 Minutes)

• Obtain a 12-lead ECG within 10 minutes to identify ST-elevation, ST-depression, T-wave inversions (suggesting ACS or PE), or diffuse ST-elevation with PR-depression (pericarditis). 2

• Draw high-sensitivity cardiac troponin immediately because myocardial injury can present with pleuritic features, and approximately 13% of patients with pleuritic chest pain have acute myocardial ischemia. 1, 2

• Measure vital signs including bilateral arm blood pressures, heart rate, respiratory rate, and oxygen saturation; tachycardia is present in >90% of PE cases. 2

• Perform a focused cardiovascular and pulmonary examination for fever, tachypnea, unilateral decreased breath sounds, dullness to percussion (suggesting effusion), crackles, and the character of the friction rub itself. 2, 3

Imaging and Laboratory Studies

• Obtain a chest radiograph (PA and lateral) as essential first-line imaging to evaluate for pneumonia, pneumothorax, pleural effusion, or masses. 2

• Dullness to conventional percussion is the most accurate physical finding for diagnosing pleural effusion (positive likelihood ratio 8.7), while the absence of reduced tactile vocal fremitus makes effusion less likely (negative likelihood ratio 0.21). 3

• If PE is suspected based on Wells criteria, proceed to CT pulmonary angiography when clinical suspicion is high or D-dimer is positive. 1, 2

• When a pleural effusion is identified, the British Thoracic Society recommends performing thoracentesis for new and unexplained effusions to determine etiology. 1

Distinguishing a Friction Rub from Other Lung Sounds

Key Differentiating Features

• Pleural friction rubs sound like creaking leather or walking on fresh snow, are coarse and grating, and are louder than crackles. 1

• Friction rubs are biphasic (heard during both inspiration and expiration) and are not cleared or affected by coughing, unlike crackles which may change with coughing. 1

• Crackles are brief, discontinuous, explosive sounds that indicate fluid in small airways or alveoli and are associated with pneumonia and pulmonary edema. 1

• Having the patient breathe deeply accentuates both sounds, but listening for the timing within the respiratory cycle (biphasic for rub, typically inspiratory for crackles) helps differentiate them. 1

Recognition Challenges

• Only 11.25% of physicians correctly identified a pleural friction rub in a recent study, compared with 55.2% for fine crackles and 74.5% for coarse crackles, indicating that friction rubs are frequently missed or misidentified. 4

• The majority of participants in a lung sound nomenclature survey did not recognize the pleural friction rub, highlighting the need for heightened clinical suspicion when pleuritic symptoms are present. 5

Management Based on Etiology

Pulmonary Embolism

• Stable patients should be transferred to the ED or chest-pain unit; hemodynamically unstable patients or those with right-ventricular enlargement require ICU admission with thrombectomy capability. 2

Pneumonia with Empyema

• Empyema requires drainage (via chest tube or surgical intervention) and antibiotics; delay in drainage is associated with increased morbidity. 1

Pericarditis

• First-line anti-inflammatory therapy consists of ibuprofen 600–800 mg three times daily for 1–2 weeks or colchicine 0.6 mg twice daily for 3 months. 2

• Beck's triad (jugular venous distension, hypotension, muffled heart sounds) together with pulsus paradoxus >10 mmHg signals cardiac tamponade and mandates urgent pericardiocentesis. 2

Critical Pitfalls to Avoid

• Do not assume a friction rub is benign viral pleurisy without excluding PE, pneumonia, and pericarditis—all of which can present identically but require urgent intervention. 1, 2

• A normal initial ECG does not exclude PE or early pericarditis; serial ECGs and troponin measurements are mandatory when clinical suspicion remains high. 2

• Sharp, pleuritic pain does not rule out acute coronary syndrome; approximately 13% of patients with pleuritic features have myocardial ischemia. 1, 2

• The absence of a friction rub on examination does not exclude pleural disease, as the rub may be intermittent or obscured by a pleural effusion. 1

• Do not delay transfer to the emergency department for additional testing when life-threatening causes are suspected; arrange urgent EMS transport immediately. 2