Dry necrosis

Dry necrosis is secondary to a severe reduction in arterial perfusion and occurs in three circumstances:

• Severe chronic ischaemia

• Acute ischaemia

Severe chronic ischaemia

Peripheral arterial disease usually progresses slowly in the diabetic patient, but eventually a severe reduction in

Arterial Embolism Foot

Fig. 6.4 (a) Neuropathic foot with infected plantar ulcer. The 4th toe has turned blue because septic arteritis has led to occlusion of both digital arteries. The 3rd toe is changing colour.

Fig. 6.4 (a) Neuropathic foot with infected plantar ulcer. The 4th toe has turned blue because septic arteritis has led to occlusion of both digital arteries. The 3rd toe is changing colour.

(b) Septic arteritis. Cross-section of digital artery showing lumen almost totally occluded by septic thrombus.

(c) Foot healed after amputation of 3rd and 4th rays.

arterial perfusion results in vascular compromise of the skin. This is often precipitated by minor trauma, leading to a cold, blue toe which usually becomes necrotic unless the foot is revascularized. Many diabetic feet with a very low pressure index do well until the skin is breached by an injury. Inflammation and successful healing make increased vascular demands which the ischaemic foot is unable to fulfil.

Many diabetic neuroischaemic patients never complain of intermittent claudication or rest pain. If the patient has concurrent retinopathy with severe visual impairment he will frequently be unaware of ulcers or necrosis. The name 'eye-foot syndrome' has been attached to cases of middle-aged or elderly men who lived alone, had undiagnosed diabetes leading to retinopathy and neuropathy, and presented late with necrosis of the feet.

Acute ischaetnia

Blue discolouration leading to necrosis of the toes is also seen in acute ischaemia, which is usually caused either by thrombosis complicating an atherosclerotic narrowing in the superficial femoral or popliteal artery or emboli from proximal atherosclerotic plaques to the femoral or popliteal arteries.

Acute ischaemia presents as a sudden onset of pain in the leg associated with pallor and coldness of the foot, quickly followed by mottling and slaty grey discolouration, and pallor of the nail beds. The diabetic patient may not experience paraesthesiae because of an existing sensory neuropathy, which also reduces the severity of ischaemic pain and may delay presentation. Some patients may complain of extreme weakness of the affected limb but not of pain.

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