A Visit to a Dangerous PAD

Abstract & Commentary

Synopsis: Peripheral arterial disease is common. Screening with measurement of the ankle-brachial index will improve detection.

Source: Collins TC, et al. Arch Intern Med. 2003;163:1469-1474.

Focusing on the populations of 3 primary care clinics and a Veterans Affairs Medical Center, Collins and colleagues sought to determine the prevalence of peripheral arterial disease (PAD). They enrolled patients who were scheduled for an appointment with their primary care physician (PCP). Inclusion criteria included age older than 50 years; after enrolling 17 patients between the ages of 50 and 54 years and discovering that none had PAD, they raised the age criterion to 55. Other criteria were ethnic and racial self-identification and having a PCP. They excluded patients who could not complete a consent form, who were demented, who had chronic obstructive pulmonary disease requiring oxygen, who were recently diagnosed with a non-skin cancer malignancy, who had leg ulcers or gangrene, who could not be contacted by telephone or who lived outside of Texas. After approaching 457 patients, 403 agreed to participate. Those who refused were more likely to be African American and younger than those who agreed.

All patients completed 4 questionnaires: the San Diego Claudication Questionnaire (SDCQ), which detects intermittent claudication; the Walking Impairment Questionnaire (WIQ), which assesses patient-reported walking ability; the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36), which measures health-related quality of life; and the Lifestyle and Clinical Survey (LCS), a complete health history questionnaire. Collins et al defined PAD as an ankle-brachial index (ABI) < 0.9. The ABI is the ratio of systolic blood pressure (SBP) in the ankle to SBP in the arm.

The patients were 34% African American, 48% male, average age 64 years, and relatively impoverished (only 5% had an annual income > $50,000). There were 67 patients (16.6%) with PAD. Patients with PAD were more likely to smoke (29.9% vs 16.7%), to be afflicted with diabetes mellitus (55.2% vs 34.5%), to be hypertensive (82.1% vs 66.4%), and to have a higher average systolic blood pressure (156.5 mm Hg vs 145.4 mm Hg). They were less likely to exercise daily (13.4% vs 25.6%), but there was no difference in the proportion that walked daily (31.3% vs 32.1%). However, patients with PAD were more likely to report the presence of intermittent claudication and atypical leg symptoms as measured by the SDCQ (62.7% vs 50.6%). A small number (1.5%) of patients without PAD reported intermittent claudication. PAD patients scored lower on the WIQ and the SF-36. There was no statistical difference between the patients with regard to use of antiplatelet drugs (38.8% vs 31.9%). Gender, age, and income did not influence results.

Only 17.9% of patients with PAD were aware of their diagnosis. A sizable proportion of them (37.3%) had no leg symptoms. When the patients were grouped by ethnicity, 13.2% of whites, 22.8% of African Americans, and 13.7% of Hispanics had PAD. This did not meet the level of statistical significance (P = 0.6). However, when the white and Hispanic populations were combined and compared with the African-American population, it was significant (P = 0.2).

Comment by Allan J. Wilke, MD

Most of the results of this study are old news,1,2 but they reinforce the lessons we learned in medical school: PAD is pervasive, but often undiagnosed. It is more common in African Americans. It is often asymptomatic. There is a lot of overlap between patients with PAD and without when considering common chronic illnesses such as diabetes, hypertension, and hyperlipidemia.

Why is the diagnosis of PAD important, and is it important enough to warrant widespread screening? PAD is a marker for other vascular disease, especially coronary and cerebral artery disease. Patients with PAD have decreased longevity, dying more frequently from heart attacks and stroke.3 The National Cholesterol Education Program’s Adult Treatment Panel III (ATP III) identifies "other clinical atherosclerotic disease" as a risk factor equivalent to established coronary heart disease, diabetes, cigarette use, and hypertension. The diagnosis of PAD could tip the scales in favor of more aggressive treatment of hyperlipidemia. Measuring ABI fulfills most, if not all, of the frame criteria for a good screening test.4

This study raises other unanswered questions. Why were so few patients taking antiplatelet medications? Only about one-third of these patients reported antiplatelet therapy, despite having conditions (diabetes, heart disease, stroke, etc) that warranted it. Why were patients with PAD less likely to exercise? Simplistically, one could argue that the condition itself hindered exercise (especially walking), but there was no difference in the percentage of patients who walked daily, notwithstanding a difference in the percentage who had leg symptoms. Why did some patients without PAD (ie, ABI > 0.9) have symptoms of intermittent claudication? Might they have microvascular disease with relatively normal large vessels?

This study can be faulted in its design. Some information was self-reported and not verified by chart review. By selecting patients from appointment lists, Collins et al did not examine that part of the population who wasn’t motivated to visit their PCP. Arguably, they were healthier and their inclusion would have lowered the incidence of PAD. Since patients with higher incomes weren’t studied, do the results apply to them? The patients who declined to participate were younger African Americans. Their inclusion presumably would have lowered the incidence of PAD in that group. I thought that Collins et al went overboard in their statistical analysis. For instance, they reported that patients with PAD had average ABIs less than patients without (0.72 vs 1.13). As my kids might say, "Well, duh!" If ABI is the variable that defines PAD, it stands to reason that people with PAD would have a lower ABI.

Dr. Wilke, Assistant Professor of Family Medicine, Medical College of Ohio, Toledo, OH, is Associate Editor of Internal Medicine Alert.

References

1. McDermott MM, et al. Arch Intern Med. 1999;159:387-392.

2. Criqui MH, et al. Circulation. 1985;71:510-515.

3. Criqui M, et al. N Engl J Med. 1992;326:381.

4. Frame PS. J Fam Pract. 1986;22:341-346.