A pleural friction rub is an adventitious breath sound heard on auscultation of the lung. The pleural rub sound results from the movement of inflamed and roughened pleural surfaces against one another during movement of the chest wall. This sound is non-musical, and described as “grating,” “creaky,” or “the sound made by walking on fresh snow.” Any potential cause of pleural effusion, pleuritis, or serositis can result in a pleural friction rub. Patients may be able to describe the localization of the rub based on pain. A pleural friction rub is a manifestation of pleural disease, though its absence does not exclude this pathology. The finding of a pleural friction rub requires prompt recognition and action on the part of the physician.
Auscultation of a pleural friction rub can occur when the normally smooth surfaces of the visceral and parietal pleura become roughened by inflammation. Pleurisy, as well as other conditions affecting the chest cavity, can cause a pleural friction rub. A pleural friction rub is a common finding in patients with pneumonia, pulmonary embolism, malignant pleural disease, and pleurisy secondary to viral infection or pancreatitis, among other causes.
Pleural friction rubs need to be distinguished from pericardial friction rub, which is a sign of pericarditis.
Recent literature does not describe the frequency of pleural friction rub in patients with a pleural disease or other chest cavity disease.
Pleural friction rub occurs when inflammation roughens the surfaces of the visceral and parietal pleura. In this setting, friction between the pleura further increases due to decreased production of lubricating fluid (pleural fluid) by the pleura. The characteristic grating sound of the pleural rub is believed to result from the release of energy when the inflamed pleural surfaces overcome the increased friction and slide past one another. Often, pleural friction rub is accompanied by pleuritic chest pain, which is characterized by sudden, intense, and sharp pain that is worse with inspiration. If the site of inflammation is near the diaphragm, pain can refer to the neck or shoulder. While the visceral pleura lacks somatic innervation and nociceptors, somatic nerves innervating the parietal pleura relay the sensation of pain. Somatic nerves innervating the parietal pleura are responsible for this pattern of pain. The visceral pleura lacks somatic innervation and nociceptors.
Patients will often complain of pleuritic chest pain, which is sudden, intense, and worse with movement such as respiration. If the underlying cause of the pleural rub is pleural effusion, patients may experience some relief from leaning forward and supporting their upper body with hands placed on the knees or another surface.
Upon palpation of the chest, the clinician may note a sandpaper-rubbing type of sensation. This sensation is suggestive of a pleural rub. The patient may complain of local tenderness with palpation, depending on the underlying etiology.
On auscultation, pleural friction rub is a non-musical, short explosive sound, described as creaking or grating, and likened to walking on fresh snow. The sound may be intermittent or continuous. A typical description of the sound is that it “sounds like walking on fresh snow.” The pleural friction rub is biphasic (heard on inspiration and expiration), usually localized to a small area of the chest, and may be accentuated by increasing the pressure on the stethoscope. The sound does not change after a bout of coughing.
Additional findings on history and physical exam will be suggestive of the underlying pathology. Important factors in the history of the patient include accompanying symptoms, history of infection, and occupational history. For instance, decreased breath sounds with increased tactile fremitus and a history of infective symptoms may increase the clinician’s suspicion for pneumonia.
Patients with an audible rub should undergo further workup. Basic blood working, including ESR, CRP, and WBC can help narrow the differential. A chest x-ray is a useful initial imaging modality to identify pneumothorax and pleural effusion. Some cases would also benefit from pleural fluid analysis. Clinicians should complete a Wells Score to determine the pre-test probability of pulmonary embolism. ECG a recommendation if there is clinical suspicion of myocardial infarction or pericarditis. Additional tests including D-dimer, arterial blood gas, ventilation-perfusion scanning, and CT pulmonary arteries may be indicated depending on the clinical context.
Pleural friction rub should resolve with management of the underlying cause. Management should focus on controlling pleuritic chest pain (if present) and treating the underlying pathological process.
For symptomatic treatment nonsteroidal anti-inflammatory medications like- aspirin, ibuprofen, or non-steroidal anti-inflammatory drugs. Antibiotics are indicated if the inflammation results from a bacterial infection.
Distinguishing a pleural friction rub from a pericardial rub is critical. In the patient with pericarditis, an inflammation of the pericardium, a grating-like sound can be heard as layers of inflamed pericardium slide against one another. Unlike a pleural friction rub, the pericardial rub will be heard even as the patient holds their breath because the movement of the pericardium has no relationship to that of the chest wall. Upon careful auscultation, the clinician will also note that the pericardial rub consists of three sounds, one systolic and two diastolic sounds. By contrast, a pleural friction rub usually has two sounds, one heard on inspiration and the second on expiration. Coarse crackles and rhonchi may also be mistaken for a pleural friction rub, but coughing will alter both of these sounds.
Pleural friction rub may also be a clinical feature in 4% of patients with pulmonary embolism of pneumonia.
Prognosis depends on the etiology of the pleural rub.
The identification of a pleural friction rub poses a diagnostic dilemma to the clinician; this is a non-specific finding with a broad differential. Excellent history-taking and documentation will facilitate identifying the cause of the rub. Life-threatening causes of pleural friction rub include pulmonary embolus and malignant pleural effusion, and rapid diagnosis and treatment have a marked effect on patient outcomes. In the emergency department setting, the clinician must rule out life-threatening causes by obtaining the requisite investigations immediately. Effective communication between the referring physician and radiologist is essential to ensure imaging assessment takes place with special attention to the myriad causes of a pleural friction rub. The care of the patient with mesothelioma will necessitate consultations with an oncologist, radiation oncologist, and surgeon, among other physician specialists. At all stages of workup and treatment, patient-centered care is to be the standard.
The prognosis of a patient with a finding of pleural friction rub depends on the underlying cause of this sign. However, to improve outcomes, prompt consultation with an interprofessional group of specialists is recommended.
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