Chapter 56 Lower Limb Peripheral Vascular Disease
Lower limb peripheral vascular disease includes arterial, venous, and lymphatic disorders (Box 56-1). Arterial disease in the lower limb can be caused by atherosclerosis, thrombosis, embolism, vasospasm, arterial dissection, or vasculitis. Venous disease in the lower limb includes venous stasis, deep venous thrombosis, thrombophlebitis, and venous insufficiency. Lymphatic disorders of the lower limb include primary and secondary lymphedema.
Arterial Disease of the Lower Limb
Lower Limb Arterial Anatomy
Knowledge of the lower limb arterial anatomy is necessary to better understand the disease process and improve patient assessment and management. The abdominal aorta divides into the two common iliac arteries at the level of the fourth lumbar vertebra. The common iliac arteries further divide into the internal and external iliac arteries. The external iliac artery passes under the inguinal ligament and then enters the thigh as the common femoral artery, which divides into the superficial and deep femoral arteries. When the superficial femoral artery reaches the level of the knee, it becomes the popliteal artery. The popliteal artery divides below the knee to become the anterior and posterior tibial arteries. The anterior tibial artery gives rise to the dorsalis pedis artery (Figure 56-1).
Atherosclerotic Peripheral Arterial Disease
Epidemiology and Risk Factors of Atherosclerotic Peripheral Arterial Disease
PAD is common in the United States, affecting around 8 million Americans.25 Men present to physicians more frequently. When screening is performed on asymptomatic individuals, however, women appear to be affected as commonly as men. Blacks are more affected than other races.41 Smoking is the biggest risk factor for PAD. Smokers are at higher risk for PAD, and they develop it at an earlier age than nonsmokers.51 Diabetes is also a major risk factor for PAD. The risk of PAD increases 26% for every 1% increase in hemoglobin A1c.58 Other factors associated with PAD include hypertension, dyslipidemia, chronic renal insufficiency, elevated inflammatory biomarkers, and hyperhomocysteinemia (Box 56-2).
Clinical Presentation of Atherosclerotic Peripheral Arterial Disease
The various clinical presentations of PAD include asymptomatic, intermittent claudication (IC), critical limb ischemia (CLI), and acute limb ischemia, with the most common being asymptomatic (Box 56-3). Only around 10% of people with PAD report symptoms of IC. Around half of PAD patients report leg symptoms other than claudication. Forty percent of people with PAD report no leg symptoms at all.25
BOX 56-3 Clinical Presentations of Peripheral Arterial Disease
Asymptomatic
The majority of PAD patients do not have the classic symptoms of IC. The absence of symptoms does not suggest a benign course. Complete occlusion of a major leg artery was found in one third of patients with asymptomatic PAD in one study.9 The lack of symptoms is due to low physical activity level rather than mild disease. Functional impairment can be present despite the lack of symptoms.30 Functional decline has been shown to be related to ankle–brachial index (ABI) even in the absence of symptoms.29
Intermittent Claudication
Classic IC is leg pain with exertion that is relieved with rest. Claudication produces ischemia in the affected muscle, which results in pain. Depending on the site of arterial disease, pain can be felt in the buttock, hip, thigh, calf, or foot. IC limits the patient’s ability to walk, which hinders community activities and exercise ability. Patients with claudication have decreased walking speed and distance, as well as decreased leg function. It has been reported that IC negatively affects physical functioning of patients more than arthritis, cancer, or chronic lung disease.6
Acute Limb Ischemia
Acute arterial occlusion of the lower limb can be caused by thrombosis, embolism, or dissection (Figure 56-2). This is a limb-threatening medical emergency. The incidence is around 140 new cases per million persons per year.41 Patients present with pain, poikilothermia, and pulselessness. They might also have the classic symptoms of pallor, paresthesia, and paralysis. Symptoms are usually present for only hours to days when the patient presents. If symptoms have been present for less than 2 weeks, it is considered to be acute limb ischemia. Acute limb ischemia requires emergent vascular surgery evaluation and treatment. Just as with myocardial infarction and stroke, reperfusion must occur as soon as possible to prevent irreversible tissue loss (muscle, nerve, or limb loss). Embolectomy and thrombolysis can be attempted in appropriate patients. Up to 30 percent of patients with acute limb ischemia will require amputation in the first month of presentation.41
Critical Limb Ischemia
CLI is chronic ischemia (Figure 56-3). CLI is ischemia of the limb for more than 2 weeks causing rest pain, ischemic ulcers, and gangrene. Because so many patients with PAD are asymptomatic, it is not uncommon for the initial presentation of PAD to be CLI. The incidence is around 500 new cases per million persons per year.41
Evaluation of Atherosclerotic Peripheral Arterial Disease
History and Physical Examination
A low awareness of PAD is found in the general public and among physicians.14 This lack of awareness, and the fact that most PAD is asymptomatic, leads to underdiagnosis of PAD. Physicians must maintain a high level of suspicion when evaluating patients at risk. Making the diagnosis of PAD is important because it has prognostic significance for impairment of mobility and physical functioning, as well as morbidity and mortality.
On physical examination, lower limb pulses should be evaluated, including the dorsalis pedis, posterior tibial, popliteal, and femoral. The presence of pedal pulses has a 90% negative predictive value for the diagnosis of PAD.41 Absent or diminished pulses, however, do not always indicate the presence of PAD but should prompt further investigation. The legs and feet should be examined for changes of skin temperature, color, and evidence of poor vascular flow. Decreased arterial blood flow to the legs can cause muscle atrophy, thin shiny skin, and decreased hair growth. Nails are often thick and brittle. The foot can appear red or purple when in the dependent position (dependent rubor) and show pallor when elevated.
Vascular Testing for Peripheral Arterial Disease
Ankle–Brachial Index
PAD is usually diagnosed with the ABI, which compares the brachial systolic pressure with the ankle systolic pressure (Figure 56-4). An ABI of 0.9 or less is 95% sensitive in detecting PAD compared with angiography. The ABI is inexpensive, simple, and noninvasive, making it an appealing screening test. An ABI should be obtained on all patients over the age of 70, patients aged 50 to 69 who have cardiovascular risk factors, or any patient with symptoms of PAD or an abnormal lower limb vascular exam.40 An ABI of 1.4 or greater is due to incompressible vessel walls at the ankle and is nondiagnostic. Patients with an elevated ABI will need additional testing such as toe pressures to evaluate for the presence of PAD. Patients with a normal ABI but a high suspicion for IC should have the ABI repeated after exercise (Figure 56-5). The ABI is related to prognosis and functional ability, and ABI can be repeated to follow disease progress.
Segmental Limb Systolic Pressure Measurement
Limb pressures are taken in the thigh, calf, and ankle. Occlusive disease is noted by a significant decrease in systolic pressure from one level to the next (Figure 56-6). Just as with the ABI, incompressible vessel walls can falsely elevate pressures and render the testing inaccurate. Small or moderate lesions can also be missed because they often do not cause a large decrease in pressure.
Segmental Plethysmography (Pulse Volume Recordings)
Pulse volume recordings are measured with a plethysmography attached to limb cuffs, and recordings are obtained at the thigh, calf, and ankle. Occlusive lesions are detected by a change in waveform from one level to the next. The accuracy of testing is greater than either test alone and increases to 95% if pulse volume recordings are combined with segmental limb pressures.57 This test is often not required because most lesions can be localized with Doppler waveform analysis.
Doppler Velocity Waveform Analysis
If a screening ABI is abnormal, Doppler waveform analysis is usually performed to localize the lesion. Doppler waveforms are obtained at multiple sites. Like pulse volume recordings, a change in waveform from one level to the next is indicative of PAD (see Figure 56-6). This test is operator dependent.
Transcutaneous Partial Pressure of Oxygen
Measurement of transcutaneous partial pressure of oxygen (TcPO2) is a useful test to predict wound healing. It can also be used to select amputation level. TcPO2 less than 30 mm Hg is associated with poor wound healing.46 TcPO2 above 40 mm Hg suggests adequate skin perfusion for healing. Readings are taken with electrodes attached to the skin. One is placed on the chest as a control, and the other is placed on the area of interest. Readings require proper positioning and temperature and can take 30 minutes to obtain.
Magnetic Resonance Angiography
Magnetic resonance angiography (MRA) is safer than intraarterial angiography. MRA sensitivity and specificity are greater than 90% for evaluating PAD.23,38 For these reasons, MRA has become the preferred imaging technique at many institutions. Contraindications are the same as with magnetic resonance imaging (MRI) in regard to the magnetic field. Some patients are unable to tolerate the procedure because of claustrophobia. Some patients are unable to lie still for the prolonged amount of time required for testing, which can cause motion artifact. There might also be artifact from stents or other hardware in the area of interest. The patient’s renal function needs to be considered before testing because nephrogenic systemic fibrosis is associated with gadolinium administration in patients with impaired renal function.
Multidetector Computed Tomography Angiography
Like MRA, computed tomography angiography (CTA) has a sensitivity and specificity greater than 90% for evaluating PAD.32 CTA is faster than MRA, which makes it more tolerable for some patients. CTA has more risk than MRA but less risk than intraarterial angiography. The risk relates to the use of iodinated contrast and radiation exposure. There can be artifact on imaging from calcium in the vessel wall.
Management of Atherosclerotic Peripheral Arterial Disease
PAD is not only underdiagnosed but it also is undertreated even after being identified.3 When treating patients with PAD, the physician and patient must remember that PAD is part of a systemic vascular disorder. Peripheral, coronary, and cerebral artery diseases are all part of systemic atherosclerosis. Patients with PAD are more likely to have coronary artery disease and cerebral artery disease than patients without PAD. Physicians and patients, however, often do not recognize PAD as an important predictor of cardiovascular morbidity and mortality and do not treat it as aggressively as coronary artery disease or cerebral artery disease.
The goals of treatment are to reduce ischemic symptoms, increase walking ability, improve function, prevent and heal wounds, prevent limb loss, and reduce morbidity and mortality. This is best accomplished using a multidisciplinary approach that includes physiatrists, primary care physicians, vascular surgeons, and the patient. Management involves education, risk factor modification, pharmacotherapy, exercise, and vascular interventions (Figure 56-7).
FIGURE 56-7 Treatment of patients with proven peripheral arterial disease.
(From Hiatt WR: Medical treatment of peripheral arterial disease and claudication, N Engl J Med 344:1608-1621, 2001.)
Risk Factor Modification
Management of patients with PAD should always include risk factor modification. Risk factor modification includes smoking cessation, weight reduction, and control of hyperlipidemia, hypertension, and diabetes. Statins have been shown to reduce mortality, coronary events, and strokes in PAD patients.37 Patients with PAD who do not have coronary artery disease should have as a goal a low-density lipoprotein (LDL) cholesterol level of less than 100 mg/dL. Patients with PAD and coronary artery disease should have a goal LDL cholesterol level of less than 70 mg/dL.41 If patients do not already have a primary care physician, they should be referred to one for aggressive management of glucose, blood pressure, and cholesterol. Patients can also be referred to a nutritionist for diet education.
It should be made clear to patients that smoking cessation can reduce their risk of amputation and cardiovascular events even if it does not improve claudication symptoms. The patient must understand the connection between continued smoking and higher risk of amputation, as well as a higher risk of cardiovascular events.26 Patients should be referred to smoking cessation programs, and the use of nicotine replacements and bupropion should be considered. Patients should be advised to stop smoking at every visit. Varenicline was recently approved for smoking cessation.
Pain Management
Patients can experience pain from IC, ischemic rest pain, ischemic ulcers, ischemic neuropathy, or concomitant diabetic neuropathy. In some patients, diabetic neuropathy can impair sensation enough that the patient cannot feel ischemic pain. Ischemic pain is best relieved by reperfusion of the limb. Exercise and risk factor modification are recommended as the first line of treatment for IC pain. Patients who continue to have moderate to severe claudication symptoms despite exercise should be evaluated for revascularization. If a patient is not a candidate for revascularization and continues to have moderate to severe IC despite an exercise program, cilostazol can be used.60 Ischemic rest pain and ischemic wounds should be treated with revascularization if the patient is a surgical candidate. Patients might also require opiates for pain control. Some patients develop rest pain at night when they lie down and find that keeping the foot in a dependent position provides relief (as opposed to nocturnal diabetic neuropathic pain, which is not relieved in the dependent position).
Wounds
Just as with ischemic pain, ischemic wounds are best treated with reperfusion of the limb (Figure 56-8). Wounds can be ischemic or neuroischemic and should be kept clean and free from necrotic debris. Sharp debridement of ischemic wounds must be done with caution because it can increase the area of ischemic necrosis. This is because the surrounding tissue might not have sufficient blood supply to repair itself after the trauma of debridement. Dry gangrene can be allowed to autoamputate as long as there is no evidence of infection and there is adequate perfusion to support healing of the underlying tissue. Appropriate orthoses and off-loading devices should be used to protect the foot from pressure and shear forces. Footwear should cover the foot to protect against trauma and have enough length, breadth, and depth to prevent pressure on the wound.
Dressings should be applied to keep the wound base clean and moist, but there is no good evidence supporting any one type of dressing over another (see Chapter 32). The wound should be monitored for infection and treated immediately if detected. The ischemic foot often has dependent rubor, which can be distinguished from cellulitis by reexamining the limb after a short period of elevation. Dependent rubor should fade with elevation and is not associated with induration or increased warmth. The erythema of cellulitis is often associated with induration, increased warmth, swelling, and does not fully resolve with elevation of the limb.
Patients with ischemic wounds should be evaluated for revascularization. TcPO2 is a useful test to predict wound healing. TcPO2 less than 30 mm Hg is associated with poor wound healing.46 If revascularization is not an option, amputation might be necessary. The physiatrist should be involved preoperatively in determining the level of amputation. The decision should be made based on tissue viability, function, and prosthetic options. Patients who undergo amputation of a limb should receive physical and occupational therapy for transfers, mobility, activities of daily living, and education. Prosthetic limbs should be prescribed for appropriate patients. See Chapter 13, Rehabilitation of People With Lower Limb Amputation, for a more detailed discussion.
Exercise
Exercise can improve walking time and walking distance in PAD patients with or without claudication symptoms.28 Exercise increases pain-free walking distance in patients with a history of IC.68 All patients should begin an exercise program, except those unable to participate in a walking exercise program because of physical, cardiac, or pulmonary reasons. Patients are encouraged to walk until they experience near maximal leg symptoms. Patient then rest until symptoms subside, and then they walk again until they experience near maximal symptoms. The patient should continue this cycle for 30 to 60 minutes two or three times a week.55 Patients without claudication symptoms should be told to exercise at a moderately hard level. Supervised exercise programs have been more successful than home exercise programs. Despite a proven benefit, supervised programs are not readily available. This is likely the result of problems with reimbursement and low patient interest.
Antiplatelet Therapy
The clinical practice guidelines from the American College of Chest Physicians recommends lifelong antiplatelet therapy for all patients with PAD, whether or not they have clinically evident coronary or cerebral artery disease.60 The intention of antiplatelet therapy is to prevent mortality and morbidity from myocardial infarction and stroke. Anticoagulation is not recommended.
Surgical Intervention
Revascularization can be through endovascular or open surgical techniques. Endovascular interventions include angioplasty, stenting, thrombolysis, and thrombectomy. Percutaneous balloon transluminal angioplasty (PTA) dilates stenosed arteries. A stent can be placed after angioplasty to decrease the chance of the occlusion recurring. Angioplasty works best in patients with focal, short lesions. Complications of PTA include hematoma, thrombosis, and embolization. Restenosis can occur.
Other surgical interventions include limb salvage and amputation. Limb salvage is an attempt to preserve the foot. Salvage procedures include debridement of wound, excision of bone, and partial foot amputations. If limb salvage is not possible or fails, an amputation at the transtibial or transfemoral level is performed. Please see Chapter 13 for a more detailed discussion about lower limb amputations.
Prognosis
Patients with symptomatic PAD have a 25% 5-year mortality rate.11 An inverse correlation exists between ABI and odds of having a myocardial infarction, stroke, or cardiovascular death.31 The risk particularly escalates once the ABI has decreased to less than 0.50.5 Up to 60% of deaths in PAD patients are from coronary artery disease; up to 20% of deaths are from cerebral artery disease; and another 10% of deaths are from other cardiovascular causes.41 Patients with PAD are at high risk for cardiovascular events and death and should be treated accordingly, with aggressive risk factor modification, cholesterol-lowering medications, and antiplatelet therapy.15
Amputation is not a common outcome for most patients with PAD but is common in certain subsets. The Framingham study found that less than 2% of patients with PAD had amputation as an outcome.20 Patients who are more likely to progress to amputation are those who smoke, have diabetes, have an ABI less than 0.50, have CLI, or have acute limb ischemia. Less than 10% of patients with PAD will develop CLI.13 Patients with PAD and diabetes are more likely to develop CLI. Patients presenting with CLI are at high risk for amputation and death. At 1 year 25% are deceased and 30% of survivors have lost a limb. Those that received a below-knee amputation as the initial primary treatment have 10% perioperative mortality, 30% 2-year mortality, and a 30% risk for further amputation.41
Thromboangiitis Obliterans (Buerger’s Disease)
Introduction
Thromboangiitis obliterans (TAO), also called Buerger’s disease, is a nonatherosclerotic PAD affecting young male smokers. It is an inflammatory disease that affects small- and medium-sized arteries of the upper and lower distal extremities. It also affects the veins and nerves, but it is the arterial aspect that causes the most morbidity. The disease is segmental, meaning there are normal-appearing sections of the artery interspersed with diseased sections. It is characterized by inflammatory thrombus in the small- and medium-sized arteries of the arms and legs that spares the vessel wall. It is considered to be a form of vasculitis.
Men are more affected by TAO than women. The number of affected women has increased, however, and is thought to be due to the increase in the number of women smoking. Although TAO is found worldwide, it is more common in Eastern Europe, the Middle East, and the Far East. It is a common cause of PAD in Japan and India. It is not a common cause of PAD in the United States. Unlike atherosclerotic PAD, life expectancy does not appear to be shortened. The risk of amputation is very high in patients with TAO.52
The cause of TAO is unknown. Although there is a clear and strong link to smoking, the exact disease-causing mechanism is still unknown. Of the patients who continue to smoke, 43% will require an amputation. Of the patients who quit smoking, only 6% will need amputation.42
Clinical Presentation, Evaluation, and Diagnosis of Thromboangiitis Obliterans
Patients typically present with claudication symptoms in the upper or lower limbs. If the patient continues to smoke, the disease will progress to rest pain and ischemic ulcers. Clinically the legs are more involved than the arms. Most patients with TAO, however, will have three or four limbs involved when assessed with angiography, even if they are symptomatic in only one limb.42 There have been case reports of disease in the vascular beds of the heart, lung, brain, kidney, and intestinal tract.17 Although some patients report arthralgias (which can appear long before the ischemic problems and typically resolve spontaneously), there is no erosive arthritis with TAO.
The physician should do a thorough history and physical examination when evaluating a patient suspected to have TAO. A tobacco history should be taken, including smoking and smokeless tobacco use. Pulses should be checked carefully in the upper and lower limbs. When evaluating a patient with leg-only symptoms, the physician can perform an Allen test to assess for asymptomatic involvement of the upper extremities (Figure 56-9). A positive test suggests small artery disease in the upper limbs but is not specific to TAO. Evidence of small artery disease in the lower and the upper limbs places TAO high on the list of differential diagnoses.
FIGURE 56-9 The Allen test.
(From Olin JW, Lie JT: Thromboangiitis obliterans (Buerger’s disease). In Cooke JP, Frohlich ED, editors: Current management of hypertensive and vascular diseases, St Louis, 1992, Mosby–Year Book.)
No diagnostic laboratory tests exist for TAO, but testing should be performed to rule out other diagnoses. Testing for autoimmune disorders and other forms of vasculitis should be performed and are negative in patients with TAO. Erythrocyte sedimentation rate and serum C-reactive protein are normal. Patients should be screened for diabetes, hyperlipidemia, and hypercoagulable disorders, which typically are not present in patients with TAO.42
No standard set of diagnostic TAO criteria has been validated, but several criteria have been proposed.33,42,43,59 Commonly accepted criteria are a history of tobacco use, age less than 45, distal limb ischemia, and exclusion of atherosclerosis and autoimmune and hypercoagulable disorders. For diagnostic criteria purposes, patients are considered to have limb ischemia if they have claudication, rest pain, ischemic wounds, or gangrene.
A biopsy should be performed if TAO is suspected, but the clinical picture is not typical. Pathologically the acute phase of TAO shows an occlusive thrombus that is inflammatory but which spares the vessel wall. The vessel wall is not spared in other vasculitides or in atherosclerosis.42
Management of Thromboangiitis Obliterans
Smoking cessation is key to disease management. It must be made clear to patients that to continue smoking means the disease will progress and the risk of amputation will be high (Figure 56-10). Almost all patients who quit smoking can avoid amputation. Patients must understand that they control the outcome of this disease by their choice to continue smoking or not. It has been reported that smokeless tobacco and nicotine replacement patches or gum can cause disease exacerbation and should therefore not be considered as safe alternatives to smoking.24
FIGURE 56-10 Patient with Buerger’s disease.
(From Stone JH: Vasculitis: a collection of pearls and myths, Rheumatic Dis Clin N Am 33:691-739, 2007.)
Revascularization is not usually a successful option for patients with TAO. Because the disease is distal and segmental, there are usually no target vessels for a bypass procedure. Trials for new treatments have been small and limited in the United States. Treatment options that have been or are being investigated either in the United States or abroad include pneumatic compression devices, prostaglandins, thrombolytics, omental transfer, electrical spinal cord stimulation, and angiogenesis. Angiogenesis has been attempted via growth factors by either direct intramuscular injection of the growth factors or gene transfer. Cell therapy has also been investigated using autologous bone marrow injection or stem cell injection. Fenestration of the tibia and intramedullary wire have also been studied.44 Although current research gives hope for the future, the mainstay of therapy continues to be smoking cessation, local wound care, and amputation when required.
