How do you differentially diagnose and manage patients with crackles versus crepitus?

Crackles vs Crepitus: Clinical Differentiation and Diagnostic Approach

Critical Distinction

Crackles and crepitus are fundamentally different physical examination findings: crackles are adventitious lung sounds heard on auscultation indicating pulmonary pathology, while crepitus refers to subcutaneous emphysema (air in soft tissues) detected by palpation, typically indicating esophageal rupture, pneumothorax, or other air leak syndromes. 1

Crackles: Pulmonary Auscultatory Findings

Mechanism and Characteristics

• Crackles are short, interrupted breath sounds generated by sudden airway opening during inspiration or closing during expiration 2, 3
• Inspiratory crackles are nearly twice as numerous as expiratory crackles and have predominantly negative polarity (76% vs 31%) 3
• Crackle pitch progressively increases during inspiration by approximately 80 Hz from early to late inspiration, reflecting recruitment of progressively smaller airways 4

Velcro Crackles: High-Yield Diagnostic Finding

Velcro crackles are dry, end-inspiratory crackles heard predominantly at lung bases that are detected in >80% of patients with idiopathic pulmonary fibrosis and should immediately prompt HRCT evaluation for interstitial lung disease. 5

• Velcro crackles are independently associated with usual interstitial pneumonia (UIP) pattern on imaging 6
• All patients with UIP pattern on HRCT and all patients with final IPF diagnosis presented Velcro crackles in one prospective cohort 6
• Unlike coarse crackles of bronchiectasis or pneumonia, Velcro crackles have a distinctive dry quality and differ from heart failure crackles, which typically clear with coughing or position change 5

Differential Diagnosis by Crackle Type

Pneumonia:

• Crackles combined with fever, localized chest pain (may be pleuritic), regional dullness to percussion, and egophony 1
• Crackles at auscultation combined with comorbidity, fever ≥38°C, and CRP >30 mg/L achieved area under ROC curve of 0.79 for bacterial pneumonia 1
• Crackles can be separated from IPF crackles with 88% specificity using automated analysis 7

Congestive Heart Failure:

• Crackles accompanied by extended neck veins, third or fourth heart sound, positive hepato-jugular reflux 1
• Crackles in CHF typically clear with coughing or position change, unlike Velcro crackles 5
• Diaphoresis, tachypnea, tachycardia, hypotension, S3, and mitral regurgitation murmur suggest acute coronary syndrome with pulmonary edema 1
• CHF crackles can be distinguished from IPF crackles with 85% specificity using computerized analysis 7

Interstitial Pulmonary Fibrosis:

• Velcro-type crackles, predominantly end-inspiratory, initially at lung bases 5
• Associated with progressive dyspnea, lower forced vital capacity (P=0.002), and lower DLCO (P=0.04) 6
• IPF crackles have distinctive acoustic features allowing separation from pneumonia (82% sensitivity, 88% specificity) and CHF (77% sensitivity, 85% specificity) 7

Crepitus: Subcutaneous Emphysema

Clinical Recognition and Urgent Causes

Crepitus detected on palpation indicates subcutaneous air and demands immediate evaluation for life-threatening conditions, particularly esophageal rupture or pneumothorax. 1

Esophageal Rupture:

• Subcutaneous emphysema (crepitus) combined with emesis and pneumothorax (present in 20% of patients) 1
• Unilateral decreased or absent breath sounds may accompany crepitus 1
• Chest pain with painful, tympanic abdomen indicates potentially life-threatening gastrointestinal etiology 1

Pneumothorax:

• Crepitus may be present with dyspnea, pain on inspiration, and unilateral absence of breath sounds 1
• Must be excluded as obstructive cause of fluid-resistant tissue hypoperfusion in septic patients 1

Algorithmic Diagnostic Approach

When Crackles Are Present:

1. Assess crackle quality and timing:

   • Dry, Velcro-type, end-inspiratory, bibasilar → Order HRCT for ILD evaluation 5, 6
   • Coarse, clear with coughing, with S3/JVD → Consider CHF, obtain BNP and echocardiogram 1, 5
   • With fever, localized pain, dullness → Obtain chest X-ray and CRP for pneumonia 1

2. Risk stratify for pneumonia if suspected:

   • Absence of runny nose + breathlessness + crackles + diminished breath sounds + tachycardia >100 + fever ≥37.8°C + CRP >30 mg/L = high risk (31% prevalence) 1
   • Low-risk patients (CRP ≤30 mg/L without above features) have only 2% pneumonia prevalence 1

When Crepitus Is Present:

1. Immediately assess for:

   • History of emesis → Consider esophageal rupture, obtain urgent chest X-ray and CT chest 1
   • Unilateral absent breath sounds → Obtain immediate chest X-ray for pneumothorax 1
   • Recent trauma or procedure → Evaluate for iatrogenic air leak

2. Transport urgently to ED if not already in hospital setting 1

Critical Pitfalls to Avoid

• Never delay transfer to ED for diagnostic testing in office setting when crepitus is detected 1
• Do not dismiss Velcro crackles as "normal aging changes"—they demand HRCT evaluation 5
• Avoid attributing all crackles to heart failure in elderly patients without considering ILD, especially if crackles don't clear with diuresis 5
• In high-risk populations (systemic autoimmune rheumatic diseases), detection of Velcro crackles should prompt ILD screening with PFTs and potentially HRCT 5
• Chest tenderness on palpation or pain with inspiration markedly reduce probability of ACS, but do not exclude pneumonia or PE 1