Rudy Bilous, MD, FRCP
Richard Donnelly, MD, PHD, FRCP, FRACP
The high-risk diabetic foot
The lifetime risk of a person with diabetes developing foot ulceration is around 25%. Recent studies suggest that the population-based incidence of diabetic foot ulcers is 1-4% with a prevalence of 4-10%. The risk of amputation is 10–30-fold higher in people with diabetes compared with the general population, and global estimates suggest that every year one million people with diabetes undergo some sort of lower limb amputation. The majority of limb amputations (85%) are preceded by foot ulceration, and the mortality rate following an amputation is reported to be in the region of 15%–40% at 1 year and 39%–80% at 5 years. The risk of foot ulceration may be lower in South Asians compared with Europeans living in the UK….
Diabetic foot ulcers are caused mainly by neuropathy (motor, sensory and autonomic) and/or ischaemia, and frequently complicated by infection. Loss of pain sensation can damage the foot directly (e.g. from ill-fitting shoes) and motor neuropathy leads to a characteristic foot posture – raised arch, clawed toes and pressure concentrated on the metatarsal heads and heel. Skin thickening (callus) is stimulated at these pressure points and the haemorrhage or necrosis, which is common within callus, can break through to form an ulcer. Callus formation is therefore an important predictor of ulcers (Figure 21.1).
Diabetic neuropathy is present in at least half of patients over 60 years of age, and increases the risk of foot ulceration sevenfold. Since peripheral nerve damage is often insidious and asymptomatic, regular inspection of the foot by patients themselves and healthcare professionals is essential to identify early signs of impending ulceration. Sensory neuropathy often renders the diabetic foot ‘deaf and blind.’ Therefore, effective and simple education about footwear, and strategies to minimise ulcer risk, are important aspects of diabetes care, especially in high-risk individuals with a history of previous ulceration and/or several risk factors (Box 21.2).
Motor neuropathy leads to muscle atrophy, foot deformity, altered biomechanics and a redistribution of foot pressures. This in turn leads to ulceration. Sensory neuropathy affects pain and discomfort, which predisposes the foot to repetitive trauma. Autonomic nerve damage leads to reduced sweating, which leads to dry and cracked skin and fissures, and so allows the entry and spread of infection. Damage to the sympathetic innervation of the foot leads to arteriovenous shunting and distended veins. This bypasses the capillary bed in affected areas and may compromise nutrition and oxygen supply. Microvascular disease may also interfere with nutritive blood supply to the foot tissues.