Nancy A. Melville

October 14, 2015

While obesity is a known risk factor for acute ischemic stroke, patients who are obese conversely show significantly lower rates of in-hospital mortality regardless of whether they received thrombolysis, a new study suggests.

The findings suggest a trend similar to the "obesity paradox" reported in nephrology and some other chronic diseases, researchers say.

"Among patients hospitalized for acute ischemic stroke, obese patients had a lower risk-adjusted in-hospital mortality," said study coauthor Urvish Patel, MBBS, MPH, from the Icahn School of Medicine at Mount Sinai, New York.

"The association of obesity and a better prognosis, [also known as] the 'obesity paradox,' needs further investigation," he concluded.

Dr Patel presented their findings here at the American Neurological Association (ANA) 2015 Annual Meeting.

National Inpatient Sample

For the study, the researchers reviewed data from the National Inpatient Sample (NIS) database from 2002 to 2012, looking at adult hospitalizations for acute ischemic stroke as a primary diagnosis using International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes.

The cohort was stratified according to use of intravenous tissue plasminogen activator (IV-tPA), and hospitalizations for endovascular procedures were excluded.

Among nearly 4.5 million acute ischemic stroke–related hospitalizations, 169,225 (3.8%) patients received IV-tPA.

Of patients who did receive IV-tPA, 13,820 (8.2%) were obese, and those patients showed significantly lower in-hospital mortality rates compared with nonobese IV-tPA recipients (6.4% vs 9.8%; P < .001). After multivariate adjustment, the adjusted odds ratio (OR) was 0.78 (95% confidence interval [CI], 0.64 - 0.94; P < .001).

Among patients who did not receive IV-tPA, 266,382 (6.3%) were obese, and those patients also showed significantly lower rates of in-hospital mortality compared with nonobese patients (2.9% vs 5.5%; P < .001).

After multivariate adjustment, the OR in that group was 0.68 (95% CI, 0.64 - 0.72; P < .001).

"The findings show that we can prove the obesity paradox in acute ischemic stroke and those who get IV-tPA and who don't get IV-tPA," Dr Patel said.

The authors also evaluated the effect of obesity on in-hospital mortality in 17,624 (7.8%) patients who underwent endovascular mechanical thrombectomy but did not find a statistically significant association in unadjusted or multivariate analysis.

Among the study's limitations is the inability to validate the ICD-9-CM codes, and because the data are from a registry, the temporal relationship of whether the stroke or the IV-tPA happened first is unknown, Dr Patel added.

Moderator Anthony Kim, MD, medical director of the UCSF Stroke Center at the University of California, San Francisco, agreed that the use of administrative data leaves some questions unanswered, particularly in terms of stroke.

"The vagaries of coding and the potential for residual confounding [in administrative data] limit the ability to really have causal inference," he told Medscape Medical News.

"There is ample evidence that the impact of stroke severity is not captured in administrative data and the outcome studied was in-hospital mortality, which can be quite different than 30-day or 90-day mortality, so this remains a preliminary and exploratory study."

Dr Kim added that some previous reports have also suggested an obesity paradox relating to stroke patients, but much more needs to be understood about the association.

"I think it is still an open question whether the obesity paradox represents an epiphenomenon explained by methodological limitations, confounding, and selection bias, or an actual entity that warrants looking for other explanations and which could impact management," he said.

Dr Patel and Dr Kim have disclosed no relevant financial relationships.

American Neurological Association (ANA) 2015 Annual Meeting. Abstract S232. Presented September 27, 2015.

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