Stroke screening “no benefit”

ABOUT 70 000 Australians have paid nearly $200 each for asymptomatic carotid artery stenosis screening, but a recent systematic review has found no evidence of benefit from such screening in the general population.

The review, published in the Annals of Internal Medicine and conducted for the US Preventive Services Task Force (USPSTF), examined evidence about screening and treating asymptomatic adults for carotid artery stenosis (CAS). It found several major flaws among 56 studies of CAS screening in the general population using ultrasound, and of carotid endarterectomy (CEA) or stenting for people with positive results. (1)

The reviewers wrote that duplex ultrasonography was a widely available, non-invasive screening test but its reliability was questionable because accuracy varied considerably among laboratories. Its use on a low-prevalence population also resulted in many false-positive results.

“Although our meta-analyses of [randomised control trials] that compared CEA with medical therapy found a reduction in perioperative stroke or death or any subsequent stroke (and other outcomes), the applicability of the evidence to current practice is substantially limited”, they wrote.

None of the trials reviewed compared endarterectomy or stenting with current best medical therapy using statins and antihypertensives, which had substantially reduced the ipsilateral stroke rate worldwide.

“The best recent evidence suggests that the incidence rate of ipsilateral stroke is nearing 1% per year, approaching the rate achieved in the surgical groups of trials that compared CEA with medical therapy”, the reviewers wrote. “This would significantly reduce the potential benefits of surgery.”

They warned of a very high false-positive rate and significant harms with screening. For instance, they estimated that among 100 000 adults in the general population, CAS screening would result in 940 true-positive results and 7920 false-positive results. If all positive tests were followed by angiography, as many as 1.2% of those people could have a resulting stroke.

Based on the review, the USPSTF has updated its recommendation statement, standing by its previous recommendation against screening for asymptomatic CAS in the general population. (2)

The statement is consistent with numerous international guidelines and with the RACGP Red Book. (3)

However, a company marketing CAS and other vascular screening in Australia told MJA InSight it did not accept the authority of the systematic review or the expert recommendations.

Screen for Life’s Australian medical director, Professor Scott Kitchener from Griffith University’s School of Medicine, said: “There are similarly ‘experts around the world’ who recommend for this type of screening, and evidence supportive of the benefits of the approach.”

He said 70 000 Australians had been screened by the company’s sonographers, mostly through a $199 vascular screening “package”, which included testing for CAS, abdominal aortic aneurysm, atrial fibrillation and peripheral artery disease.

In a statement with the company’s US-based chief medical officer Dr Andrew Manganaro, Professor Kitchener suggested the review’s conclusions were not relevant because they were based on patients undergoing vascular surgery after a positive result, whereas in reality, most positive cases would be treated with lifestyle interventions or medication.

“People with abnormal screening results are referred to their GP for diagnosis, monitoring and potentially treatment”, the statement said.

They cited an audit of patients who had attended Screen for Life as evidence that undergoing screening could “improve behaviour change in lifestyle interventions by making risk factors more tangible and real”.

However, this claim was dismissed by Dr John Quinn, director of vascular surgery at Brisbane’s Princess Alexandra Hospital.

“You don't need an expensive test to be told you need to change your lifestyle if you are over 60 and overweight”, Dr Quinn said.

“There is no evidence that general population screening is worthwhile.”

Professor Paul Glasziou, professor of evidence-based medicine at Bond University, Queensland, said he knew of several people who had received an “invitation” from Screen for Life, and said he would not personally undergo screening unless he developed symptoms, such as a TIA.

“When patients have asked me about screening, I have asked about their standard cardiovascular risk factors — blood pressure, cholesterol, smoking, diabetes, etc”, he said. “These are simpler [to assess], proven, and we can do something direct about them. I suggest they avoid additional screening.”

An Annals of Internal Medicine editorial accompanying the systematic review said the population attributable risk for stroke related to asymptomatic CAS was just 0.7%, and was dwarfed by other population attributable risk (PAR) factors such as hypertension (PAR > 95%), atrial fibrillation (PAR, 1.5%‒24%), cigarette smoking (PAR, 1.2%‒14%) and hyperlipidaemia (PAR about 9%). (4)

“All risk factors should be managed aggressively, regardless of the presence or absence of an asymptomatic CAS”, it said.

National Stroke Foundation Clinical Council member Dr Bruce Campbell said addressing hypertension, cholesterol and the usual risk factors was the appropriate course for patients worried about cardiovascular disease.

1. Ann Intern Med 2014; Online 7 July
2. Ann Intern Med 2014; Online 7 July
3. RACGP: Guidelines for preventive activities in general practice 8th edition
4. Ann Intern Med 2014; Online 7 July