Pleural Friction Rub: A Characteristic Sound Heard On Auscultation In Pleurisy

What is pleural friction rub?

A pleural friction rub is a distinctive sound heard during auscultation, indicating that inflamed and roughened pleural surfaces are rubbing against each other. The sound is often described as grating, creaky, or squeaking. If you have difficulty imagining it, think of the sound of walking on fresh snow. This noise can be unsettling, leaving you to wonder about its cause. Pleural friction rub is most commonly associated with pleurisy but can also result from pleural effusion or serositis.¹

What causes it? 

Your lung is covered by two membranes that separate the lung surface from the inner part of the chest wall. These thin membranes are called the pleura, while the space between them is the pleural space. Normally, your pleural space is filled with a small amount of lubricating fluid that reduces friction between the pleural layers and ensures the lungs can move easily against the chest wall.^2,3

However, several conditions can disrupt this normal state, causing inflammation and irritation of the pleura. This irritation makes the pleura rough and dry, leading to a scratchy sound known as a pleural friction rub. The main cause of a pleural friction rub is pleurisy, which is also known as pleuritis. Other conditions that may produce this sound include:

• Pleural effusion: Fluid accumulation in the pleural space due to various conditions, most commonly pneumonia (a lung infection that causes inflammation of the air sacs).
• Serositis: Inflammation of the serous tissues in the body, including the linings of the lungs, heart, and abdominal organs. It can be caused by autoimmune conditions or other factors.
• Pulmonary embolism: A blockage in the pulmonary arteries in the lungs.
• Chest Injuries: Trauma to the chest can lead to pleural inflammation.

Each of these conditions can cause the pleura to become irritated and inflamed, resulting in the characteristic sound of a pleural friction rub during auscultation.^1,2

Understanding pleurisy

Most cases of pleural friction rub are found in pleurisy patients. Pleurisy occurs when the pleura becomes inflamed, often due to infections (bacterial or viral), cancer, autoimmune diseases such as lupus or rheumatoid arthritis, or chest injuries. The inflammation leads to roughening of the pleural surfaces, which then produces the characteristic friction sound. The main symptom is a sharp, stabbing chest pain that worsens when breathing deeply, coughing, or moving. Other symptoms include cough, fever, and feeling unwell.

In patient assessment, the doctor may perform a physical examination that includes auscultation. When they detect this typical pleural friction rub, it helps them establish a diagnosis of pleurisy. They may order additional tests to confirm the diagnosis and rule out other differential diagnoses.

People with pleurisy may develop complications such as pleural effusion and pneumothorax. Adequate treatment is essential to achieve the best outcome and prevent complications. Treatment focuses on addressing the underlying cause and managing pain. This may include antibiotics for bacterial infections, anti-inflammatory medications, or procedures such as thoracocentesis to drain fluid buildup, if present.³

Detecting a pleural friction rub

During a physical examination, your doctor uses a stethoscope to detect a pleural friction rub. Typically, you will be asked to sit upright and breathe while the doctor listens to all areas of the lung surface. A pleural friction rub is a short and explosive sound that is often described as creaking or grating. It is similar to the sound of walking on fresh snow. The sound can be intermittent or continuous and is usually heard in areas where the inflamed pleurae are in contact. It is more clearly heard in the lower parts of the chest or on the sides.

The timing of the pleural friction rub is crucial; it is often heard at both the beginning and end of the breathing cycle, which helps distinguish it from other respiratory sounds like wheezes or crackles. Notably, the pleural friction rub sound does not change after a bout of coughing, further helping in its identification.^1,5

Similar sounds to distinguish

There's another sound called a pericardial rub that's crucial to distinguish from a pleural friction rub. When patients experience inflammation of the pericardium - the sac filled with fluid that protects the heart and great vessels, known as pericarditis - they may produce a distinct sound detectable through auscultation. This inflammation can result from infections, autoimmune diseases, heart attacks, or injuries to the heart or pericardium. The sound is characterised by a grating-like noise produced as the inflamed pericardium slides against itself.

Unlike the pleural friction rub, where the sound correlates with the movement of the chest wall during breathing, in the pericardial rub, the sound persists even when the patient holds their breath. Additionally, while the pleural friction rub typically has two sounds heard during inspiration and expiration, the pericardial rub consists of three sounds: systolic and diastolic components.

Conditions such as coarse crackles and ronchi may also be mistaken for a pleural friction rub. However, coughing can alter crackles and ronchi sounds, while in a pleural friction rub, it doesn’t change.^6,7

Treatment and management

The treatment for pleural friction rub focuses on addressing the underlying causes and managing pleuritic chest pain for your comfort. This may involve:

• Antibiotics for bacterial infections
• Antivirals for viral infections
• Anti-inflammatory drugs for autoimmune conditions
• Other medications are based on the specific underlying disease

To relieve symptoms, healthcare providers may recommend nonsteroidal anti-inflammatory medications such as aspirin, ibuprofen, or other NSAIDs.¹

FAQs

Which characteristic would describe a pleural friction rub?

A pleural friction rub is a scratchy and high-frequency sound heard during auscultation with a stethoscope. It is described as a grating and creaky sound during both inspiration (inhale) and expiration (exhale). You can imagine it as "walking on fresh snow”.⁸

Does pleural friction rub go away on its own?

A pleural friction rub will go away if the underlying cause is treated. The main cause of a pleural friction rub is pleurisy, which is inflammation of the pleura. Pleurisy can result from bacterial infections, viral infections, autoimmune diseases, cancer, chest trauma, or other conditions. While most causes require treatment, viral infections can be self-limiting, meaning they resolve on their own, so there is a possibility the pleural friction rub will go away on its own.⁹

Can you hear pleurisy with a stethoscope?

Yes, you can hear pleurisy with a stethoscope. 

What are the signs of pleural effusion on auscultation?

During auscultation, pleural effusion presents with decreased or absent breath sounds, especially in the area affected by the effusion. The fluid in the pleural space alters the vibration of lung tissue, leading to these changes. On percussion, a dullness will be heard. Additionally, tactile fremitus (the vibrations felt on the chest wall when a person speaks) will be reduced.

What does a pleural friction rub indicate?

A pleural friction rub indicates that the pleural layers (the membranes lining the lungs and chest cavity) are inflamed. Normally, a small amount of fluid acts as a lubricant, preventing the layers from rubbing against each other during breathing. When these layers become inflamed, they become rough, leading to the grating and scratching sound heard during inspiration and expiration.¹

Summary

A pleural friction rub is a grating, creaky sound heard during the auscultation of the lungs indicating that roughened and inflamed pleural layers are rubbing against each other. This noise can occur due to various causes, but it typically results from pleurisy.

Pleurisy is an inflammation of the pleural layer caused by infections, autoimmune diseases, cancer, chest injuries, or others. The inflammation leads to roughening of the pleural surfaces, producing the characteristic friction sound. During a physical examination, your doctor will use a stethoscope to detect a pleural friction rub. You will usually be asked to sit upright and breathe while the doctor listens to different areas of your lung surface. A pleural friction rub is a nonmusical, short, explosive sound, often described as creaking or grating, similar to the sound of walking on fresh snow.

The treatment for this pleural friction rub depends on the underlying causes. If the cause is an infection, for example, you will be given antibiotics. Medications to relieve symptoms, such as nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin or ibuprofen, may also be prescribed.