pleural friction rub

**Pathophysiology:** Normally, the visceral and parietal pleura are separated by a thin layer of lubricating pleural fluid and glide silently. Inflammation, fibrinous exudate, or tumor deposits roughen the pleural surfaces, so they rub against each other with respiratory movement. The result is a creaking, scratching, "leather-on-leather" sound.

**Exam characteristics:** - Heard in both inspiration and expiration (biphasic), often described as "to-and-fro." - Localized, usually over the lower lateral chest wall, where lung excursion is greatest. - Not cleared by coughing. This helps distinguish it from rhonchi and crackles, which may change with coughing. - Persists when breath is held? No. It stops with breath-holding because the surfaces stop moving. This distinguishes it from a pericardial friction rub, which continues with breath-holding because it follows the heartbeat. - Often accompanied by sharp, localized pleuritic chest pain, which patients may relieve by splinting or lying on the affected side. - Can be palpable (a "grating" fremitus). - Typically disappears when a large effusion separates the pleural layers. Pain and the rub may resolve as the effusion develops.

**Common causes:** - Pneumonia with parapneumonic involvement (the most common cause) - Pulmonary embolism with infarction - Viral pleuritis (e.g., coxsackie B, "devil's grip"/Bornholm disease) - Autoimmune disease: SLE, rheumatoid arthritis - Malignancy (mesothelioma, metastases) - Tuberculosis - Uremia (uremic pleuritis/pericarditis) - Asbestos-related pleural disease - Drug-induced lupus (e.g., hydralazine, procainamide)

**Differential from a pericardial friction rub:** - Pleural rub: varies with respiration, stops with breath-holding, and is usually heard at the lung bases or lateral chest. - Pericardial rub: heard best at the left lower sternal border with the patient leaning forward and exhaling. It is classically triphasic (atrial systole, ventricular systole, ventricular diastole), does not change with breath-holding, and is associated with pericarditis.

**Workup and management:** - Chest X-ray (effusion, infiltrate, mass) and chest CT if needed. Consider CT-PA if PE is suspected. - Ultrasound and thoracentesis if an effusion is present. - Treat the underlying cause, such as antibiotics for pneumonia, anticoagulation for PE, or NSAIDs for viral or inflammatory pleurisy.

**Board pearls:** - A pleural rub plus pleuritic pain strongly suggests pleural inflammation. - Breath-holding stops a pleural rub but not a pericardial rub. - Consider PE with infarction in a patient with pleuritic pain, dyspnea, and risk factors. - Consider SLE in a young woman with pleuritis, arthralgias, and rash. - Pleuritic pain with a rub that suddenly resolves may signal the development of a pleural effusion.