Epidemiology of Diabetic Neuropathies

A summary of some recent epidemiological reports on the prevalence of diabetic neuropathy is provided in table 2. As can be seen, these studies, all A summary of some recent epidemiological reports on the prevalence of diabetic neuropathy is provided in table 2. As can be seen, these studies, all

The studies of epidemiological features of autonomic neuropathies are less consistent and give conflicting data for the prevalence of autonomic dysfunction and also predictive factors.

Clinical Features of Diabetic Neuropathies

Mononeuropathies Isolated peripheral nerve lesions are recognized as being more common

in diabetic patients, particularly in older individuals with type 2 diabetes. These mononeuropathies occur not infrequently in the absence of other complications but as with all neuropathic syndromes, may be the presenting feature of type 2 diabetes.

Cranial Mononeuropathies The nerves supplying the extraocular muscles (particularly the third nerve)

are most commonly affected: these ophthalmoplegias tend to be of relatively rapid onset and not infrequently are associated with some pain. Diplopia is the usual presenting feature, and exclusion of other causes, particularly space-

occupying or vascular lesions, is essential, usually by computerized tomog- raphy. The natural history of the cranial mononeuropathies is of spontaneous recovery in a matter of months.

Isolated and Multiple Mononeuropathies Almost any peripheral nerve may be affected but those particularly likely

to be involved include the median nerve (carpal tunnel syndrome), the peroneal nerve (foot drop) and the lateral cutaneous nerve of thigh (meralgia paraesthetica). Mononeuritis multiplex simply describes the occurrence of more than one isolated mononeuropathy at the same time in an individual patient.

Truncal Mononeuropathy This rare neuropathy is characterized by pain occurring in a band distribu-

tion around the chest or abdomen in a dermatomal pattern. It typically occurs in isolation, but truncal polyneuropathy is recognized that is also rare, but tends to occur in association with other long-term complications.

Polyneuropathies Diabetic Amyotrophy (Proximal Motor Neuropathy)

This typically affects older male type 2 diabetic patients and presents with pain, wasting and weakness in the proximal muscles of the lower limb, either

unilaterally or with symmetrical bilateral involvement. These patients invari- ably have evidence of a peripheral sensory motor neuropathy in addition, and weight loss may be an accompanying feature. As in all neuropathies, the diagnosis is one of exclusion of nondiabetic causes and a thorough search for internal malignancy may be required.

Autonomic Neuropathies Involvement of the autonomic nervous system in diabetes can affect any

area receiving autonomic innervation, but although dysfunction can frequently

be found using sophisticated autonomic function tests, severely symptomatic autonomic neuropathy remains relatively rare. Symptoms and signs of autonomic dysfunction may typically involve the cardiovascular, gastrointestinal, urogenital, thermoregulatory and sudomotor function.

Cardiac autonomic neuropathy is rarely symptomatic, although an in- crease in heart rate secondary to vagal denervation may be found with no response to respiration or the Valsalva manoeuvre. Similarly, although a pos- tural drop in systolic blood pressure is a not uncommon finding in diabetic patients with neuropathy, it is rarely symptomatic.

Gastrointestinal autonomic dysfunction may be manifested by abnormalities in motility and secretion. The two major clinical problems are diabetic gastroparesis which may present with nausea, postprandial vomiting, and diabetic diarrhoea which tends to be worse at night and interspersed by periods of normal function or even constipation.

Abnormalities of sudomotor function are common but are often neg- lected. Reduced sweating in the feet due to sympathetic denervation is a contributory factor in the pathogenesis of diabetic neuropathic foot problems. In contrast, truncal sweating, particularly at night, can be troublesome and gustatory sweating (profuse sweating in the head and neck region on eating certain foods) is a highly characteristic symptom of autonomic dysfunction which is also seen in patients with diabetic nephropathy.

Peripheral Sensory Neuropathies Chronic distal sensorimotor is the commonest of all these syndromes that

may have very diverse clinical features. At one extreme patients may have severe symptoms of pain (characteristically worse at night), paraesthesiae,

Table 3. Stages of diabetic peripheral sensory neuropathy Stage of neuropathy

Characteristics

No neuropathy

No symptoms or signs

Clinical neuropathy Chronic painful

Burning, shooting, stabbing pain × pins and needles; increased at night; absent sensation to several modalities; reduced/absent reflexes

Acute painful Severe symptoms as above (hyperaesthesia common); may fol- low initiation of insulin in poorly controlled diabetes; signs minor or absent

Painless with complete/ Numbness/deadness of feet or no symptoms; painless injury; partial sensory loss

reduced/absent sensation; reduced thermal sensitivity; absent reflexes

Late complications Foot lesions; neuropathic deformity; nontraumatic amputation Types of diabetic neuropathy: frequent, sensorimotor symmetrical neuropathy (mostly

chronic, sensory loss or pain), autonomic neuropathy (history of impotence and possibly other autonomic abnormalities); rare, mononeuropathy (motor involvement, acute onset, may be painful), diabetic amyotrophy (weakness/wasting usually of proximal lower limb muscles).

Staging does not imply automatic progression to the next stage. The aim is to prevent, or at least delay, progression to the next stage. From Boulton et al. [1998], with permission of J. Wiley & Sons.

allodynia and pins and needles, usually most predominant in the feet and lower legs. Motor manifestations include small muscle wasting in the more severe cases, and absent ankle reflexes. The onset of these symptoms is insidious or gradual and should be contrasted with the much rarer acute sensory neuropathy in which patients have very severe symptoms, but few signs: this type of neuropathy frequently follows a period of metabolic instability.

At the other extreme some patients may never experience neuropathic symptoms, but gradually lose sensation in the feet to such an extent that the presenting feature may be insensitive trauma to the feet. It is therefore essential that all diabetic patients have their feet examined on a regular basis, as diabetic peripheral neuropathy cannot be diagnosed without such a thorough examina- tion. These stages of diabetic peripheral sensory neuropathy are summarized in table 3.

Table 4. Annual review: screening for neuropathy History

Exam

Presence/absence of

Use a disposable instrument, e.g. neuropathic symptoms

Pin-prick test

a disposable dressmaker’s pin Do not use a hypodermic needle Nature of symptoms

Ask ‘Is it painful?’ not ‘Can you feel? (positive/negative?)

Light touch

Use a consistent method, ideally a cotton wisp

Duration/progression of

Use a 128-Hz tuning fork, initially on symptoms

Vibration test

the big toe

Nocturnal exacerbation?

Ankle reflex

Compare the ankle reflex with the knee reflex

History of insensitive

Absence of sensation in the foot to a 10 g injury/ulcers?

Pressure perception

monofilament may be used to assess the risk of foot ulceration

Epidemiology of Diabetic Neuropathies