The metabolic syndrome (MetS) remains a complex medical condition often not completely understood by clinicians and patients alike. Although there are no consensus criteria, the definition often cited is one by the National Cholesterol Education Program's Adult Treatment Panel III (ATP III), which lists 5 easily determined clinical parameters and requires 3 of them to be present to make the diagnosis. These factors are increased abdominal waist circumference, elevated triglycerides (TG), low high-density lipoprotein cholesterol (HDL-C), high blood pressure, and an elevated fasting glucose level. Patients so identified as having MetS are at higher risk of developing cardiovascular disease and/or type 2 diabetes, and thus should be targeted for therapy after reducing their low-density lipoprotein cholesterol (LDL-C) levels to goal.1
In this article, the authors looked at the presence of the MetS in older chronic obstructive pulmonary disease (COPD) patients who participated in a cardiopulmonary rehabilitation program (CPRP). In a small but prospective evaluation, 38 COPD patients and 34 control subjects in a CPRP matched for age, gender, and body mass index were evaluated for the MetS. Results showed that 47% of subjects with COPD met at least 3 of the 5 criteria, compared with 21% of the control group. Not surprisingly, the most obese, comprising the "blue bloater" phenotype, had an even higher incidence (75%) of the MetS.
What was surprising was the low prevelance of MetS in the control group. Since in patients older than 50, the incidence of the MetS in the United States is about 44%,2 selection factors in a small group may best explain this. Of note, this was not a diverse population group as was used for the Third National Health and Nutrition Examination Survey (NHANES III) data analysis. The small COPD group appeared to represent stable COPD disease with moderate to severe airflow obstruction. This is similar to the GOLD COPD guidelines, which state that pulmonary rehabilitation should be added to any patient with stage II disease (moderate) or worse.3
What can we learn from this report? We would like to focus on factors that influence the diagnosis of MetS in patients with COPD. For example, 73% of women in the COPD group were on hormone replacement therapy (HRT) compared to none in the control group. Estrogens can raise TG, while lowering HDL-C, with the opposite effects seen with the progestin component. Glycemic control may improve with HRT. Thus, the kind of hormone replaced can influence the diagnostic criteria for MetS.4,5 In addition, although the authors did control for recent oral glucocorticoid use in the 3 months prior to the study, we should note that steroids, often used in patients with COPD, can raise TG and HDL-C.4 On the other hand, terbutaline can raise HDL-C values. Of course, continued cigarette smoking lowers HDL-C.4Table 1 summarizes some of the factors that influence the diagnosis of MetS in COPD patients.
The authors are correct to point out that an atherogenic diet, weight gain, and a sedentary lifestyle in COPD patients are potential risk factors for developing the MetS. Improving these causative factors with intensified lifestyle change may ideally occur in a pulmonary rehabilitation program and further research to learn how to do this more effectively with the COPD patient is encouraged.
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