The diabetic neuropathies are a heterogeneous group of conditions that may be sub-classified into various poly-neuropathies and mononeuropathies. The commonest forms of diabetic neuropathies are:
• distal sensorimotor neuropathy (also called peripheral neuropathy)
• autonomic neuropathy .
Distal Sensorimotor Neuropathy/Peripheral Neuropathy Epidemiology/Aetiology
• This affects about 30% of patients with both types of diabetes.
• Its prevalence increases with both age and duration of diabetes .
• The onset of this type of neuropathy is gradual and insidious.
• In the majority of affected individuals, it is asymptomatic; however, 15-25% have symptoms.
• Typical symptoms include paraesthesia, hyperaesthe-sia, and sharp, stabbing, shooting and burning pain, all of which are exacerbated at rest and particularly at night.
• Walking and/or exercise often relieve symptoms and this can be an important discriminator between neuropathic pain and the rest pain of critical limb isch-aemia .
• Clinical examination usually reveals a sensory deficit in a glove and stocking distribution.
• Signs of motor dysfunction are usually present, with wasting of the small muscles of the hands and feet and absent ankle reflexes.
• The 10-g monofilament, used to test pressure perception, and the biothesiometer, used to test the vibration perception threshold, are also simple adjunctive tests used to investigate and identify those at risk for foot ulceration.
• Inability to perceive the 10-g monofilament has been associated with a tenfold increased risk for foot ulceration .
• Vibration perception threshold >25 V has been associated with a fourfold increase in risk for ulceration in comparison with a group with a vibration perception threshold of 13 V over a 10-year period of follow-up .
• The diagnosis of peripheral neuropathy is made easily by assessment of large fibre function (e.g. loss of vibration perception using a 128-Hz tuning fork), small fibre function (e.g. hot-cold rod and/or pin-prick sensation) in the feet, together with assessment of ankle reflexes.
• A composite score of these modalities, the modified neuropathy disability score, has been evaluated in prospective studies and it was found to discriminate the patients at risk for foot ulceration .
• A particularly dangerous situation is the "painful-painless leg". In this situation the patient has severe painful symptoms, but the examination reveals severe sensory loss; such patients are at great risk of painless injury to their feet .
• Diabetic neuropathy is the common denominator in 85% of diabetic foot ulcers. Two cross-sectional studies confirmed the frequency of neuropathy in patients presenting with new foot ulcers. In London , 87% of patients with ulcers had neuropathy (62% primarily neuropathic and 25% neuroischaemic ulcers), where as in Manchester  85% of patients with ulcers had neuropathy (40% neuropathic ulcers, 45% neuroisch-aemic).
• Other prospective studies have also established that the presence of neuropathy was associated with a several-fold increase in foot ulceration [1, 72, 92].
• Optimal glycaemic control is important in the prevention of diabetic neuropathy.
• A number of drugs (mainly antidepressants and anticonvulsants) can relieve symptoms of painful diabetic neuropathy.
• At present, there are no drugs that have an effect on the natural history of neuropathy, which is one of gradual deterioration of nerve function .
• In addition, the loss of sympathetic control of arterio-venous shunting results, in the absence of peripheral vascular disease, in increased blood flow and warm feet with distended dorsal foot veins .
• However, the highest-risk foot is the pulseless insensitive foot, because it indicates the presence of somatic and autonomic neuropathy together with peripheral vascular disease.
• The interaction between the causative pathways to foot ulceration is summarized in Fig. 8.1.2.
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