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Peripheral arterial disease (PAD), a major cause of disability, loss of work, and lifestyle changes in the United States, is defined as obstruction of blood flow into an arterial tree excluding the intracranial or coronary circulations. PAD is mostly silent in its early stages, but when lesion obstruction exceeds 50%, it may cause intermittent claudication with ambulation. Further disease progression typically leads to rest pain or frank tissue loss. However, some patients may remain asymptomatic with severe disease because of extensive collateralization in the lower extremity. Estimates of the prevalence of intermittent claudication vary by population, from 0.6% to nearly 10%; the rate increases dramatically with age. Approximately 20% to 25% of patients will require revascularization, while fewer than 5% will progress to critical limb ischemia. Limb loss, although rare, is associated with severe disability and an overall poor prognosis, with 30% to 40% mortality in the first 24 months after limb loss. As with coronary artery disease, the most common cause of symptomatic obstruction in the peripheral arterial tree is atherosclerosis, a systemic inflammatory process in which cholesterol-laden plaque builds up in the artery and eventually blocks the lumen. Typical risk factors include age, gender, diabetes, tobacco abuse, hypertension, and hyperlipidemia. [ABSTRACT FROM AUTHOR]