diabetes prevalence and cardiovascular risk in South Asians.
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Chaturvedi N, Abbott CA, Whalley A, Widdows P, Leggetter SY, Boulton AJ.
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3 Diabetic Neuropathy Solomon Tesfaye
INTRODUCTION
Polyneuropathy is one of the commonest complications of the diabetes and the commonest form of neuropathy in the developed world.
Diabetic neuropathy encompasses several neuropathic syndromes the commonest of which is chronic distal sensorimotor symmetrical neuropathy (abbreviated to ‘distal symmetrical neuropathy’), the main initiating factor for foot ulceration.
The epidemiology of distal symmetrical neuropathy has recently been reviewed.1 The European Diabetes (EURODIAB) Prospective Complications Study, which involved the examination of 3250 type 1 patients, from 16 European countries, found a prevalence rate of 28% for distal symmetrical neuropathy.2 Indeed, several clinic-2,3 and population-based studies4,5 show surprisingly similar prevalence rates for distal symmetrical neuropathy, affecting about 30% of all diabetic people at any time and 50% after 15 years of diabetes.
There is now little doubt that glycaemic control is a key determinant of the development of the microvascular complications of diabetes, including distal symmetrical neuropathy.2,6−8 Age2,4 and duration2,4,5 of diabetes are well-established correlates of distal symmetrical neuropathy.
Cigarette smoking,2,4 both background and proliferative retinopathy2,4,5 and microalbuminuria2 have also been reported to be associated with distal symmetrical neuropathy.
However, most of the studies with regard to the epidemiology of distal symmetrical neu- ropathy have been cross-sectional and thus the observed associations with the various risk factors can be misleading, as true causality can be demonstrated only in a prospective fashion.
To date, few studies have assessed risk factors for neuropathy prospectively, and findings have been conflicting.
Hypertension was observed to be a strong risk factor for distal symmetrical neuropathy in 463 young, type 1 subjects in the Epidemiology of Diabetes Complications (EDC) follow-up study.9 In contrast, in type 2 patients, hypoinsulinaemia was identified as a key risk factor for neuropathy incidence,10 while a mixed population follow-up suggested that the type of diabetes and microvascular disease were associated with the severity of distal symmetrical neuropathy.11 Recently the results of the EURODIAB Prospective Study, which included a large cohort of type 1 patients, were published: After excluding those with neuropathy at baseline, the study showed that over a 7-year period, about one quarter of type 1 diabetic patients developed distal symmetrical neuropathy, with age, duration of diabetes and poor glycaemic control being the major determinants.12 The development of neuropathy was also associated with potentially
The Foot in Diabetes, 4th Edition. Edited by Andrew J.M. Boulton, Peter R. Cavanagh and Gerry Rayman. C 2006 John Wiley & Sons, Ltd. ISBN: 0-470-01504-7
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DISTAL SYMMETRICAL NEUROPATHY 31
modifiable cardiovascular risk factors such as serum lipids, hypertension, body mass index and cigarette smoking.12 Furthermore, cardiovascular disease at baseline carried a twofold risk of neuropathy, independent of cardiovascular risk factors. In summary, based on recent epidemiological studies, correlates of diabetic neuropathy in- clude increasing age, increasing duration of diabetes, poor glycaemic control, retinopathy, albu- minuria and vascular risk factors (hypertension, obesity, smoking and hyperlipidaemia).1,2,4,12
DISTAL SYMMETRICAL NEUROPATHY This is the commonest neuropathic syndrome affecting over 90% of diabetic patients with neuropathy and this is what is meant in clinical practice by the phrase ‘diabetic neuropathy’.
Sensory loss starts in the toes and then extends to involve the feet and legs in a ‘stocking’ distri- bution.
When sensory loss is well established in the legs, the upper limbs may be involved in a ‘glove’ distribution, starting with the fingers.
Diabetes can affect the autonomic nervous system, and in patients with distal symmetrical neuropathy subclinical autonomic neuropathy is com- mon, although clinical autonomic neuropathy is rare.
With disease progression, motor manifes- tations such as wasting of the small muscles of the hands and limb weakness become apparent.
The main clinical presentation of distal symmetrical neuropathy is sensory loss, which the patient may not be aware of, or may be described as ‘numbness’ or ‘dead feeling’.
How- ever, some may experience a progressive build-up of unpleasant sensory symptoms including tingling (paraesthesiae); burning pain; shooting pains down the legs (like ‘electric shock’); lancinating (knife-like) pains; contact pain or hypersensitivity often with daytime clothes and bedclothes (allodynia); pain on walking often described as ‘walking barefoot on marbles’, or ‘walking barefoot on hot sand’; sensations of heat or cold in the feet; persistent achy feeling in the feet and cramp-like sensations in the legs.
Within a 24-h period the same patient with painful diabetic neuropathy may perceive a variety of painful symptoms including seemingly contradictory sensations of intense heat and cold in the feet.
To the external observer these may seem inherently contradictory but as Huskisson remarked ‘pain is a purely subjective experience and the external observer cannot play any part in its assessment’13 and so we have no choice but to take the patient’s word for it.
In addition, a patient may experience dull aching pain and ‘numbness’ or ‘dead feeling’ of the lower limbs (a ‘negative’ symptom as opposed to ‘positive’ symptoms of burning, shooting and lancinating pains).
Occasionally, pain can extend above the feet and may involve the whole of the legs, and when this is the case there is usually upper limb involvement also.
It is also important to appreciate that there is a large spectrum of severity of these symptoms, ranging from minor complaints such as tingling in a toe or two, to severe painful neuropathy involving both legs.
This has implications on management strategy for the patient.
Painful diabetic neuropathy is characteristically more severe at night, and often pre- vents sleep.14,15 Some patients may be in a constant state of tiredness because of sleep deprivation.14,15 Others are unable to maintain full employment.14−17 Severe painful neuropathy can occasionally cause marked reduction in exercise threshold, which interferes with daily activities.
This is particularly the case when there is an associated disabling, severe postural hypotension due to autonomic involvement.
Not surprisingly therefore, depressive symptoms are not uncommon.17 As discussed in Chapter 6, it is important to appreciate that many subjects with distal symmetrical neuropathy may not have any of the above symptoms, and their first presentation