Pleurisy and pleural friction rub
In one sentenceA pleural friction rub arises outside the airway, in the inflamed pleural layers. This is why it is superficial and localised and does not change with coughing.
- A superficial, creaking sound that recurs over a small area, often with pleuritic pain.
- It is mainly a localising sign. It does not show the cause.
- Its absence does not exclude pleural inflammation. Recognition depends on the observer.
Yes. Roughened pleural layers stick and slip, and a new sound arises outside the airways. If fluid collects and separates the layers, this sound may disappear.
Not the main change.
If fluid collects, the breath sounds beneath it are also diminished.
A localised, superficial, creaking sound. It does not change with coughing.
For the reasoning: Where does sound come from? · How does sound reach the chest wall? · How do adventitious sounds arise? · From sound to differential diagnosis
What do you hear?
Over a small area you hear a creaking or crunching sound that seems very close to your ear. It may occur in inspiration, in expiration or in both, and it repeats at a similar point with every breath. The patient often describes pain in the side that gets worse on breathing in.
Why does it sound like this?
Inflammation and fibrin roughen the pleural surfaces. As the lung and chest wall slide past each other, tangential tension builds up and is released at intervals. This stick-slip movement, in which the surfaces alternately catch and slide, produces a series of short, non-musical impulses.
Distinguishing clues
- Cough: A rub persists after coughing. Sounds from secretions, by contrast, may change.
- Site: It is heard over a small area and can change markedly within a few centimetres.
- Breath-holding: A pleural rub stops when the patient holds their breath. A rub that continues with the heart rhythm suggests a pericardial source.
- Can be confused with coarse crackles: Repeated impulses can sound like coarse crackles, and their waveform looks similar too. The superficial quality, the pain and the lack of response to coughing tell them apart.
Pitfalls
- It does not show the cause. The cause may be infection, pulmonary infarction, autoimmune pleuritis or malignancy. Do not forget the possibility of pulmonary embolism.
- Its absence does not exclude pleural inflammation. Even among experienced clinicians, agreement in recognising recorded friction rubs is limited.
- As fluid collects between the surfaces, they move apart and the rub may disappear. Its disappearance does not always mean improvement.
Next step
Imaging (chest X-ray, lung ultrasound, and CT if needed) and assessment of the cause. Assess the possibility of pulmonary embolism and infarction clinically.
Try this pattern in a case
Going deeperresidents · specialists · numbers and sources
The source: a lubricated interface
The pleural space is a lubricated, coupled interface. It is incomplete to think of it simply as two dry surfaces rubbing together. The recorded sound depends on local surface roughness, the normal force (the force pressing the surfaces together), tangential displacement and the way the vibration reaches the chest wall.
Waveform evidence
On phonopneumography, rub recordings showed more heterogeneity in the polarity of the first deflection than pulmonary crackles. They also varied more with small changes in recording site. This is consistent with a spatially complex surface source. It supports the view that rubs and crackles arise from mechanically different systems.
A pitfall in digital analysis
A short pleural impulse can fall in the same duration range as a discontinuous airway sound. Repeated impulses can look like a series of crackles. Respiratory phase, focal distribution, persistence after coughing and, in difficult cases, simultaneous pleural imaging help to tell them apart.
Terminology and agreement
In a survey of breath sound terminology, agreement in recognising recorded pleural friction rubs was limited, even among physicians familiar with lung auscultation. A convincing rub sharpens the anatomical question. Its absence is weak negative evidence.
See the reference list for sources.