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Joshua Koulack, MSc, M.D., FRCS
Section of Vascular Surgery, Department of Surgery, University of Manitoba,
Winnipeg, MB Introduction
It has been well established that persons with diabetes have a greater prevalence and severity of peripheral vascular disease (PVD) than the general population. More than 80% of persons with diabetes for more than 20 years will develop some form of vascular disease and 75% will die as a result of complications from vascular disease1 such as stroke or myocardial infarction. Both large and small vessels are affected, which can contribute, alone or in concert with the often-encountered sensorimotor polyneuropathy, to the complications seen in the feet of persons with diabetes.
History
The mildest symptom of lower extremity vascular insufficiency is claudication. This typically presents as a cramping discomfort in the buttock or calf muscles on walking a certain (highly reproducible) distance. Several minutes of rest relieves the pain after which the same distance can once again be attained before the discomfort recurs. Occasionally, there is no pain but rather the sensation that the limb is "giving out". Patients with intermittent claudication are unlikely to progress to limb threatening ischemia if close attention is given to risk factor management (smoking, hypertension, hypercholesterolemia, obesity, and hyperglycemia).
More severe occlusive disease may manifest as rest pain or night pain. Rest pain is usually a severe burning discomfort in the forefoot (at the periphery of the circulation), which is constant. Night pain is rest pain that wakes the patient from sleep. It is related to having the feet level and is resolved by hanging the feet over the edge of the bed (to gain the advantage of gravity to aid arterial pressure) or walking slowly around (thereby decreasing venous pressure and increasing tissue perfusion pressure). Each of these is consistent in their pattern, not variable, and is a sign of a threatened limb. The critically ischemic diabetic foot may be pain free due to peripheral neuropathy.
Physical Examination
The ischemic limb may show signs of inadequate nutrition with loss of muscle bulk, atrophy of skin, loss of hair growth on the dorsum of the toes and foot, and thickening of toenails secondary to slowing of nail growth. Often the foot is shiny, scaly and ruborous. Ankle and foot edema may be prominent due to chronic limb dependency for control of the ischemic pain.2 The diabetic foot may be ruborous because of superficial vasodilatation and arteriovenous shunting as a result of autonomic neuropathy. Examination for femoral, popliteal, posterior tibial and dorsalis pedis pulses can help localize the level of the occlusive disease. If pedal pulses are palpable, vascular reconstruction is almost never required.
Vascular Investigations
If concern is raised about the adequacy of the peripheral circulation, an objective noninvasive evaluation is warranted. Systolic ankle to brachial blood pressure ratio (ankle/brachial index or ABI) is helpful in determining if vascular intervention is necessary. ABI of 1.0 is considered normal, <0.90 may indicate occlusive disease, 0.50-0.80 there likely exists a single segment occlusion and <0.50 is commonly found in patients with multilevel occlusion.3 Persons with diabetes may have calcification of the media rendering their vessels incompressible and the ABI erroneous. This is suggested if the systolic BP at the ankle is >300 mmHg, >75 mmHg higher than the brachial systolic BP or the ABI is >1.30. If there are incompressible vessels at the ankle, toe pressures are measured. A Toe Systolic Pressure Index (TSPI) of > 0.60 is considered normal. If the absolute toe pressure is <30 mmHg, healing is unlikely to occur.
Measuring tissue PO2 can also assess the likelihood of healing. Tissue PO2 >30 mmHg should heal, whereas that <20 mmHg is unlikely to heal and <10 mmHg is not compatible with healing.3 Although the tissue PO2 provides valuable information, it is not available in all centres.
If the patient presents with clinical signs of a threatened limb and the ABI is inadequate, the next investigation is angiography. Angiography is performed only to plan intervention, not as a diagnostic test, and should be obtained only after consultation with a vascular surgeon.
Complications
If ulceration is present, it is important to note the location, the duration of the ulcer, whether it began spontaneously or was related to trauma, and whether it is increasing or decreasing in size. Gangrene may be "dry" or "wet", the former being a more benign entity resulting from ischemia, the latter being infected and more immediately threatening.
Aggressive diabetic foot infections require prompt identification and surgical intervention even in the face of adequate circulation. Even with appropriate antimicrobial therapy, the infection can result in a neutrophilic vasculitis causing localized small vessel thrombosis4 and rapid advancement of the necrotic tissue margin to the point where limb loss is inevitable. A deep plantar space infection can present with severe pain and little to find on superficial examination. Usually necrotizing infections present with violaceous discoloration of the skin and a foul odor.
Outcomes of Intervention
When limb salvage and survival rates are considered for individuals with ischemic lower extremities, the postoperative mortality rate is significantly higher in persons with diabetes than without.5 Better graft patency rates are observed in limbs where good distal runoff compared to where poor runoff is observed. The person with diabetes should be made aware that there is a high incidence of amputation even after successful revascularization, particularly in those individuals with severe occlusive disease within the foot.6 An alternative to vascular bypass is angioplasty. Angioplasty is reserved for individuals with a limited occlusive lesion in an easily accessible vessel.
Summary
Peripheral vascular disease with underlying limb ischemia in the person with diabetes is a serious and significant complication which may have catastrophic consequences. The first line of investigations should be noninvasive vascular study to evaluate the adequacy of peripheral circulation. Should the circulation be deemed inadequate to support healing of lesions, it is, therefore, prudent to proceed to angiography if the patient is a surgical candidate. Non-surgical adjunctive measures may be of benefit, however, their success and benefit have not been unequivocally proven. If doubt exists as to how to proceed with an ischemic appearing lesion, it would be prudent to contact a vascular surgeon for an urgent opinion.
References
- Peterson C.M., Kaufman J., and Jovanovic L. Influence of Diabetes Mellitus on Vascular Disease and Its Complications. In: Moore WS, ed. Vascular Surgery: A Comprehensive Review. 5th ed. Philadelphia, PA: W.B. Saunders Co.; 1998: 146-167
- Management of Peripheral Arterial Disease (PAV). Trans Atlantic Inter-Society Concensus (TASC). Section C: Acute Limb Ischemia. Eur J Vasc Endovasc Surg, 19 (Suppl A): S144-243, 2000.
- Orchard T.J., Strandness D.E. Jr.: Assessment of Peripheral Vascular Disease in Diabetes. Report and Recommendations of an International Workshop Sponsored by the American Diabetes Association and the American Heart Association September 18-20, 1992 New Orleans, Louisiana. Circulation, 88 (2):819-828, 1993.
- Edmonds M.E.: Progress in Care of the Diabetic Foot. Lancet, 354: 270-272, 1999.
- Karacagil S., Almgren B., Bowald S., Bregqvist D.: Comparative Analysis of Patency, Limb Salvage and Survival in Diabetic and Non-Diabetic Patients Undergoing Infrainguinal Bypass Surgery, Diabet Med, 12 (6): 537-41, 1995.
- Toursarkissian B., Hassoun H.T., Smilanich R.P., Godsey J.B., Sykes M.T.: Efficacy of Infrainguinal Bypass for Limb Salvaging Young Diabetic Patients, J Diabetes Complications 14 (5): 255-258, 2000.
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