The Hoover's Sign of Pulmonary Disease: Molecular Basis and Clinical Relevance
© Johnston et al; licensee BioMed Central Ltd. 2008
Received: 28 December 2007
Accepted: 05 September 2008
Published: 05 September 2008
In the 1920's, Hoover described a sign that could be considered a marker of severe airway obstruction. While readily recognizable at the bedside, it may easily be missed on a cursory physical examination. Hoover's sign refers to the inspiratory retraction of the lower intercostal spaces that occurs with obstructive airway disease. It results from alteration in dynamics of diaphragmatic contraction due to hyperinflation, resulting in traction on the rib margins by the flattened diaphragm. The sign is reported to have a sensitivity of 58% and specificity of 86% for detection of airway obstruction. Seen in up to 70% of patients with severe obstruction, this sign is associated with a patient's body mass index, severity of dyspnea and frequency of exacerbations. Hence the presence of the Hoover's sign may provide valuable prognostic information in patients with airway obstruction, and can serve to complement other clinical or functional tests. We present a clinical and molecular review of the Hoover's sign and explain how it could be utilized in the bedside and emergent management of airway disease.
Suggested Indices Of Severity Of Airway Obstruction
Pursed lip breathing
Intercostal retraction (Hoover Sign)
Accessory muscle use
Pulmonary function (FEV1 and FEV1/FVC)
Peak Expiratory Flow Rate
Better clinical and bedside prognosticators of airway obstruction would be helpful as asthma and COPD are becoming increasingly prevalent in the population . COPD is the fourth leading cause of death in the United States behind coronary artery disease, malignancy, and cerebrovascular disease. In 2000, an estimated 10 million US adults reported physician-diagnosed COPD. Data from the Third National Health and Nutrition Examination Survey (NHANES III), however, estimate that among 11 million US adults with evidence of low lung function, < 40% reported a diagnosis of COPD or asthma, suggesting that COPD is under-diagnosed. Acute exacerbations of COPD can result in ventilator failure, and patients with severe COPD or asthma are more prone to developing this complication. A clinical, quickly identified manifestation of respiratory failure is the Hoover's sign, which does not require expensive tests or waiting for radiological or biochemical results (such as arterial blood gases). Moreover, when patients presents with an acute exacerbation of airway disease in the emergency room or in a physician's office, they are less likely to tolerate laborious radiological examinations (such as computed tomograms) and pulmonary function tests (which require intense patient participation). It is in this situation that a positive Hoover's sign, in association with other clinical parameters, blood gases or peak expiratory flow tests is likely to assist in patient triage and management in emergency settings. We present a review of the clinical and molecular/structural basis of the Hoover's sign and explain how it could be utilized in the bedside and emergent management of severe airway disease.
Clinical presentation of Hoover's sign
What is Hoover's sign?
Originally described in 1920 by Hoover, this eponymous sign refers to the paradoxical inspiratory indrawing of the lateral rib margin which has been attributed to direct traction on the lateral rib margins by the flattened diaphragm [2, 3]. Normally, the costal margin moves very little during regular breathing, but, if it does, it moves outward and upward. In patients with obstructive airway disease there is a higher tendency for it to move paradoxically . In these patients, paradoxical movements of the sternum as well as of the abdominal wall may be seen . Garcia-Pachon et al., found Hoover's sign expression in 62 out of 82 patients with COPD (sensitivity of 76%), 3 out of 23 patients with asthma (13%) and in 3 out of 101 (3%) of patients with congestive heart failure . In a larger study of 157 patients, the same investigators demonstrated presence of Hoover's sign in 71 patients (45% of study population), and in 36%, 43% and 76% respectively of patients with mild, moderate or severe COPD . Garcia-Pachon also showed that patients with COPD and Hoover's sign tended to have a higher dyspnea index/score, have higher hospitalizations or emergency room visits than patients without the sign . It appears that Hoover's sign may provide excellent prognostication of severe COPD. In a multivariate analysis, severity of dyspnea, the patient's body mass index, numbers of exacerbations historically and numbers of prescribed drugs were independently associated with the sign .
The Hoover's Sign of Hysterical Paralysis, not to be confused with the sign being discussed, can be found in the neurological literature that describes a sign to separate organic from non-organic paresis of the leg. Involuntary extension of the paralyzed leg occurs when flexing the contralateral leg against resistance. The patient lies supine, the examiner's hand is placed under the non-paralyzed heel, and the patient is asked to elevate the paralyzed leg. In organic paresis the examiner feels a downward pressure under the non-paralyzed heel; in malingering no pressure is felt. This sign is not within the purview of the current review.
Presumed molecular mechanisms behind Hoover's sign
Clinical significance of Hoover's sign
Hoover's sign is a frequent finding in COPD, and the frequency increases with severity. The sign can also be present in patients with congestive heart failure, asthma, severe pneumonia (especially in children), bronchiolitis, as well as seen unilaterally in diaphragmatic paralysis, pleural effusion and pneumothorax.
The Hoover's sign is reported to have a sensitivity of 58% and specificity of 86% for detection of airway obstruction in a study by experienced respiratory medicine specialists among a group of first year residents in family medicine . The study compared the accuracy of Hoover's sign detecting obstructive airway disease compared with traditional signs such as wheezing, rhonchi and/or reduced breath sounds. Observer agreement in the study (kappa statistic) was 0.74 for Hoover sign and was lower for the rest of the signs stated above . The Hoover's sign had a positive likelihood ratio of 4.16, which was higher than that of the other signs. Obstructive airway disease in the study was defined as an FEV1/FVC ratio of < 0.70. There have been no studies conducted on the sensitivity and specificity of Hoover's sign in asthma. There is no data available either on the cost savings that may be induced by using Hoover's sign as opposed to use of chest roentgenography, pulmonary function tests or arterial blood gases, for example. The duration of persistence of Hoover's sign, its appearance or disappearance in relationship to exacerbations and remissions and the influence of aggressive therapy on extent of retraction are hitherto unknown. Further studies would certainly improve insights into the pathogenesis of airway obstruction but probably would be unlikely to be done in this day and age of high technology and digital imaging.
Hoover's sign refers to the inspiratory retraction of the lower intercostal spaces. It results from alteration in dynamics of diaphragmatic contraction due to hyperinflation, resulting in traction on the rib margins by the flattened diaphragm. Seen in up to 70% of patients with severe obstruction, this sign is associated with body mass index, dyspnea and frequency of exacerbations. This sign can be an excellent marker for severe airway obstruction.
Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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