How do you differentiate between pleural effusion and pleurisy based on lung sounds and patient-reported pain when breathing?

Differentiating Pleural Effusion from Pleurisy by Auscultation and Pain Characteristics

The presence of a pleural friction rub on auscultation indicates pleurisy (pleural inflammation), while diminished or absent breath sounds with dullness to percussion indicates pleural effusion; pleuritic pain occurs in both conditions but is more characteristic of early pleurisy before significant fluid accumulation.

Lung Sound Findings

Pleural Effusion

• Diminished or absent breath sounds over the affected area due to fluid dampening sound transmission 1
• Dullness to percussion over the fluid-filled area 1
• Decreased tactile fremitus as fluid blocks vibration transmission 2
• No pleural friction rub once significant fluid accumulates, as the inflamed pleural surfaces are separated by fluid 1

Pleurisy (Pleural Inflammation Without Significant Effusion)

• Pleural friction rub - a creaking, grating sound heard during both inspiration and expiration when inflamed pleural surfaces rub together 1
• Normal or near-normal breath sounds if no significant fluid has accumulated 1
• Normal percussion unless minimal fluid is present 2
• The friction rub may disappear if effusion develops, as fluid separates the inflamed pleural surfaces 1

Pain Characteristics

Pleuritic Pain (Present in Both Conditions)

• Sharp, stabbing chest pain that worsens with deep breathing, coughing, or movement 1
• Approximately 75% of patients with pulmonary embolism and pleural effusion have pleuritic pain, demonstrating this symptom's presence in effusions 1
• Pain is typically localized to the side of involvement 1

Pain Patterns That Help Differentiate

Pleurisy (without significant effusion):

• Severe, sharp pleuritic pain is the predominant symptom 1
• Pain may be disabling and persistent in chronic cases 1
• The friction rub is audible and correlates with the painful area 1

Pleural Effusion:

• Dyspnea becomes the dominant symptom as fluid accumulates, occurring in more than half of cases 1
• Pleuritic pain may be present initially but often diminishes as fluid separates the pleural surfaces 1
• Pain is described as dull and aching rather than sharp pleuritic in conditions like mesothelioma with large effusions 1
• Dyspnea is often out of proportion to effusion size, particularly with pulmonary embolism 1, 3

Critical Clinical Algorithm

Step 1: Perform thorough auscultation

• If friction rub is present → suggests active pleurisy (with or without minimal effusion) 1
• If diminished breath sounds with dullness → suggests significant pleural effusion 1, 2

Step 2: Assess pain-to-dyspnea ratio

• Predominant sharp pleuritic pain with minimal dyspnea → favors pleurisy without significant effusion 1
• Predominant dyspnea with dull pain or resolved pleuritic pain → favors pleural effusion 1

Step 3: Consider effusion size on imaging

• Small effusions (less than one-third hemithorax) may still have pleuritic pain and friction rub 1, 3
• Large effusions typically have absent friction rub and predominant dyspnea 1

Important Clinical Pitfalls

• Do not assume absence of pleuritic pain excludes pleural effusion - approximately 25% of patients with pulmonary embolism and effusion do NOT have pleuritic pain 1
• Chronic severe pleuritic pain is rare in asbestos-related pleural disease despite extensive pleural thickening, so persistent pain should prompt evaluation for other causes 1
• A friction rub may be present transiently in early pleural effusion before fluid accumulation separates the pleural surfaces 1
• Malignant effusions often present with dull, aching pain rather than sharp pleuritic pain, which can mislead clinicians 1

When Clinical Examination Is Insufficient

• Ultrasound is the preferred investigation to confirm fluid presence and can detect volumes as small as 20 mL 4
• Lateral chest radiographs may reveal fluid not apparent on posteroanterior views 1
• Clinical assessment alone correctly identified all transudates in one series, but atypical features warrant thoracentesis 1