Screening for Shortness of Breath: Stretching the Screening Paradigm to Tertiary Prevention

Screening is a population strategy for finding as yet undiagnosed disease in individuals without symptoms. Dyspnea screening is conceptually different because individuals have symptoms. We have provided a rationale for dyspnea screening.

Shortness of breath, or dyspnea, an uncomfortable subjective breathing sensation that is distressful or unpleasant in nature, causes anxiety because the shortness of breath feels out of proportion to the degree of effort exerted.^1,2 By contrast, an exercising athlete, for example, will not complain of dyspnea because a degree of respiratory difficulty is expected. Dyspnea prevalence increases with age from as low as 2.4% in the population aged 18 years and older to 32% in the population aged 70 years and older.¹ Most importantly, when dyspnea is determined by questionnaire, it has shown a reproducibility of more than 90%,² making this a valid (persistent, not random) symptom to use for screening purposes in epidemiological studies.

SHORTNESS OF BREATH AND MORTALITY STUDIES

We examined a systematic review ending in March 2013 that included 10 cohort studies of at least 500 participants and controlled for age, smoking, and lung function.¹ Dyspnea (determined by questionnaire) was an exposure, mortality an outcome. Six studies found a 1.3- to 2.9-fold greater risk of all-cause mortality in those with dyspnea when followed starting at age six to eight years and continuing until age 43 years.¹ Four of these studies looked at cardiovascular disease mortality and found an increased risk of death that was 1.6- to 2.3-fold greater in those with dyspnea.¹

Two additional longitudinal studies were found after the 2013¹ summary, and neither controlled for lung function. The first was a study of 21 379 twins (8672 complete twin pairs) who were followed for 28 years.³ Participants with persistent dyspnea at baseline had a 1.41-fold (95% confidence interval [CI] = 1.31, 1.52) greater hazard (risk) of death than did those without dyspnea.³ This increased to 2.64-fold (95% CI = 1.21, 5.74) in discordant within-pair monozygotic twins.³

The second study followed 11 533 adults from Bangladesh for 11 to 12 years and found a 1.90-fold (95% CI = 1.32, 2.74) greater risk of all-cause mortality in those with dyspnea at baseline.⁴ In addition, those with dyspnea had significantly increased cause-specific mortality from chronic obstructive pulmonary disease, asthma, heart disease, pulmonary heart disease, tuberculosis, and lung cancer with hazard ratios of 6.39 (95% CI = 3.81, 10.72), 9.31 (95% CI = 3.88, 22.34), 1.88 (95% CI = 1.24, 2.84), 5.80 (95% CI = 1.60, 21.03), 2.27 (95% CI = 1.02, 5.05), and 2.85 (95% CI = 1.32, 6.16), respectively.⁴

The review of 10 studies¹ and the twins study³ used the Medical Research Council (MRC) dyspnea questionnaire (available as a supplement to the online version of this article at http://www.ajph.org). The Bangladesh study asked a single question—whether the respondent had dyspnea—with a dichotomous (yes vs no) response.^2,4 Using these baseline questionnaires, all 12 studies found a significant increase in all-cause, cardiovascular disease, or cause-specific mortality. The diseases people with dyspnea were dying of were primarily heart or lung related.^1,4

RATIONALE FOR DYSPNEA SCREENING

Dyspnea detection by questionnaire revealed a low pulse oximeter saturation (which is one way to detect the disease) in 13% (7/54) of individuals who were dyspneic but did not have a clinical diagnosis of disease.² The argument for detecting dyspnea earlier by screening is further strengthened by the approximately twofold greater mortality found in all studies when using dyspnea as exposure with a decade or longer follow-up.^1,3,4 This “protracted” time frame suggests that detection of dyspnea with a definitive diagnosis of the diseases resulting in dyspnea is possible and that the extended time before a mortality outcome will allow treatment. It has now been demonstrated that many with chronic dyspnea are dying from chronic treatable diseases, such as chronic obstructive pulmonary disease, asthma, heart disease, tuberculosis, and the less treatable disease, lung cancer.⁴

Furthermore, heart disease, chronic respiratory diseases, and lung cancer currently comprise one third of all deaths in the United States and a major portion of deaths worldwide. This is at least partly related to smoking—felt to be the number one cause of worldwide preventable mortality, with an estimate of five million deaths annually.⁵ This means that up to one third of all individuals who have died may have had shortness of breath many years before death. This again suggests that it would be reasonable and worthwhile to screen for dyspnea, particularly among those who are middle aged and older.

Where is dyspnea in routine encounters with health professionals? A recent survey of general practitioners in Australia recorded 98 000 encounters from 988 physicians. Dyspnea and shortness of breath were not present in the top 20 list of patient reasons for the encounter.⁶ Clearly, during these encounters or routine health visits, a simple question related to the presence or absence of dyspnea should be asked and would undoubtedly help detect some with shortness of breath.

DETECTION OF DYSPNEA

Dyspnea detection by questionnaire is straightforward. It can be done by asking whether one had dyspnea in the last six months in a simple dichotomous (yes vs no) question.¹ Or the screener could use some modification of the MRC question: “Do you have to walk slower than most people on the level? Do you have to stop after a mile or so (or after one quarter hour) on the level at your own pace?”⁷ This is the MRC grade three level dyspnea question, which most studies have used in some form when evaluating dyspnea as a mortality predictor.¹ The MRC breathlessness scale (available as a supplement to the online version of this article at http://www.ajph.org) questions graded one to five take seconds to answer⁷ and can be placed on a routine health survey. An MRC dyspnea grade of three or higher predicts mortality.^1,3

If dyspnea is detected, the patient can be referred to a health care facility. A history, clinical examination, and pulse oximetry can be done and if warranted a chest imaging study. From these noninvasive tests most causes of dyspnea will be found because two thirds to 85% of dyspnea is felt to be secondary to diseases of the heart and lungs as well as anxiety reactions and neurologic diseases.^1,2,4

DYSPNEA SCREENING AND TERTIARY PREVENTION

As seen in Figure 1, traditional screening detects disease before symptoms are present. Screening for dyspnea (by questionnaire) poses a different problem. As seen in Figure 2, clinical disease has already occurred when dyspnea is a symptom. This reduces the lead time to make a diagnosis because the asymptomatic preclinical period has passed, resulting in the inability to delay symptomatic disease.

FIGURE 1—

Traditional Screening for Disease Detection

Note. Traditional screening for disease detection occurs during the preclinical latent period (i.e., the period after which disease is detectable but before symptoms appear).

FIGURE 2—

Questionnaire Screening for Dyspnea

Note. Disease, as manifest by dyspnea, has to occur before screening can detect disease; therefore, dyspnea screening with disease detection would result in tertiary prevention.

Therefore, any intervention would be for tertiary prevention; that is, the traditional screening framework (Figure 1) shows that screening should occur before symptoms (and clinical disease) appear rather than after symptoms and clinical disease occur (Figure 2). We suggest that with diseases resulting in dyspnea, screening will save lives because disease will be detected before many individuals seek medical attention and diagnosis and treatment will begin earlier.

CONCLUSIONS

Traditional screening looks for disease in asymptomatic, often higher risk, individuals and may have a low yield among all screened. By contrast, dyspnea screening searches for disease in individuals who have symptoms but do not yet know they have disease. If a dyspnea screen is positive, the yield for disease should be high (i.e., the disease is symptomatic).

Models need to change to accommodate new information. The traditional secondary prevention screening paradigm is reasonable but needs to adjust and expand to accommodate dyspnea screening. It is often said that prevention is better than cure. For dyspneic diseases, tertiary prevention intervention will be more in the nature of reducing morbidity and mortality because cure is less likely.