Hoover Sign in Pulmonology
The Hoover sign refers to paradoxical inward movement of the lower lateral rib cage during inspiration, serving as a clinical marker of severe airway obstruction and diaphragmatic dysfunction in COPD. 1
Physical Examination Technique
The sign is identified by observing the lower intercostal spaces during inspiration—instead of the normal outward expansion, the lower ribs move paradoxically inward. 1 This finding requires careful observation and can be missed on cursory examination, though inter-observer agreement is excellent (κ statistic = 0.8) when examiners are properly trained. 2
Pathophysiologic Mechanism
The paradoxical rib motion results from diaphragmatic flattening due to hyperinflation. 1 When the diaphragm becomes flattened from chronic air trapping, its contraction generates inward traction on the rib margins rather than the normal outward expansion. 1 This altered mechanical advantage reflects fundamental changes in respiratory muscle dynamics. 1
Diagnostic Performance
- Sensitivity: 58-76% for detecting airway obstruction 1, 3
- Specificity: 86-94% for COPD diagnosis 1, 3
- The sign is present in approximately 49-76% of patients with severe COPD (GOLD stages 3-4) 2, 3
- Only 3% of patients with congestive heart failure demonstrate this sign, making it highly specific for obstructive disease 3
Associated Clinical Features
Patients with Hoover sign demonstrate significantly worse respiratory mechanics and clinical outcomes:
- Lower maximal inspiratory pressure (MIP): 39 cmH₂O versus 58 cmH₂O in those without the sign (p<0.001) 2
- Higher MEP/MIP ratio: 1.88 versus 1.16 (p<0.001), indicating disproportionate inspiratory muscle weakness 2
- Greater air trapping: RV/TLC ratio of 65% versus 59.5% (p=0.014) 2
- More severe obstruction: Lower FEV₁% values (p<0.005) 4
Prognostic Implications
The presence of Hoover sign identifies a high-risk COPD phenotype with worse outcomes:
- Higher dyspnea burden: MRC dyspnea scale 2.2 versus 1.0 (p<0.0001) and Borg scale 5.6 versus 3.1 (p=0.0001) in patients without the sign 5
- Increased healthcare utilization: 0.87 versus 0.27 hospitalizations per year (p=0.005) 5
- More emergency visits: 2.5 versus 0.9 per year (p=0.01) 5
- Greater frequency of exacerbations 1
Importantly, these worse outcomes occur regardless of the degree of functional impairment measured by spirometry alone, suggesting the sign captures additional prognostic information beyond FEV₁. 5
Clinical Utility
The Hoover sign provides valuable bedside information for:
- Confirming severe airway obstruction in dyspneic patients (specificity 94% for COPD versus other causes of dyspnea) 3
- Identifying patients at higher risk for exacerbations and hospitalizations who may benefit from more aggressive management 5
- Detecting diaphragmatic dysfunction without requiring formal respiratory muscle testing 2
- Complementing spirometry and other functional tests in risk stratification 1
Common Pitfalls
Do not confuse Hoover sign with other causes of paradoxical breathing:
- Bilateral diaphragmatic paralysis causes paradoxical inward abdominal movement, not specifically lower rib retraction 1
- Asthma rarely produces this sign (present in only 13% of asthmatic patients) 3
- The sign requires adequate observation time during quiet breathing—rushed examination will miss it 1
The correlation between FEV₁ and dyspnea scales is significant only in patients with Hoover sign (r=0.48-0.49, p<0.05), suggesting the sign identifies patients whose symptoms more closely track with objective airflow limitation. 5