What is the Hoover sign?

What is the Hoover Sign?

The Hoover sign is the paradoxical inward movement of the lower lateral rib cage during inspiration, serving as a clinical marker of severe airway obstruction in chronic obstructive pulmonary disease (COPD). 1, 2

Physical Examination Technique

• The sign is identified by observing the lower lateral rib cage during inspiration—instead of the normal outward expansion, the ribs move inward paradoxically 1, 2
• Examination should focus on the lower intercostal spaces bilaterally, watching for inspiratory retraction of these areas 2
• The sign has good inter-observer reliability with a kappa statistic of 0.8 when examiners are properly trained 3

Diagnostic Performance

• Hoover's sign has a sensitivity of 58% and specificity of 86% for detecting airway obstruction 2
• The sign is present in approximately 45% of stable COPD patients overall, but frequency increases dramatically with disease severity 1
• It is not detected in mild COPD, appears in 36% of moderate COPD, 43% of severe COPD, and 76% of very severe COPD patients 1

Pathophysiologic Mechanism

• The sign results from diaphragmatic flattening due to hyperinflation, not from direct inward pull by the diaphragm itself 4
• As lung volume increases toward total lung capacity, the zone of apposition (where diaphragm contacts the rib cage) decreases, causing negative pleural pressure to dominate rib motion 4
• The flattened diaphragm loses its normal mechanical advantage and can no longer effectively lift the ribs outward during contraction 4, 5
• This represents altered diaphragmatic geometry with increased curvature radius and decreased efficiency 5

Associated Clinical Features

In multivariate analysis, Hoover's sign is independently associated with: 1

• Higher dyspnea scores
• Higher body mass index
• Increased number of exacerbations
• Greater number of prescribed medications

Pulmonary function correlates include: 1, 5, 3

• More severe airflow obstruction (lower FEV1%)
• Greater degree of air trapping (higher RV/TLC ratio, specifically 65% versus 59.5% in those without the sign) 3
• Lower maximal inspiratory pressure (MIP: 39.0 versus 58.0 cmH2O) 3
• Higher MEP/MIP ratio (1.88 versus 1.16), suggesting diaphragm dysfunction 3

Clinical Significance and Pitfalls

• The presence of Hoover's sign indicates severe disease and provides valuable prognostic information beyond spirometry alone 2
• The sign may be easily missed on cursory examination—deliberate observation of the lower rib cage during inspiration is required 2
• Hoover's sign should not be confused with other eponymous signs in medicine (such as Hoover's sign of leg paresis in functional neurologic disorders, which is an entirely different clinical finding)
• The sign reflects both the severity of obstruction and the degree of hyperinflation, making it a useful bedside marker for disease progression 1, 5

Practical Application

• Use Hoover's sign as part of the physical examination in all patients with known or suspected COPD to assess disease severity 2
• When present in GOLD stage 3 or 4 COPD, consider measuring respiratory pressures (MEP/MIP) as the sign correlates with diaphragm dysfunction 3
• The finding should prompt aggressive management of hyperinflation and consideration of interventions to reduce air trapping 1
• Serial examination for development of Hoover's sign may help track disease progression in patients with moderate COPD 1