Diabetic peripheral neuropathy can be defined as: ‘The presence of symptoms and/or signs of peripheral nerve dysfunction in people with diabetes after other causes have been excluded.’ (Boulton et al, 1998).
Peripheral neuropathy is perhaps the most common (approximately 50%) and a familiar complication that affects the feet of people with diabetes (Kumar et al, 1994). Prevalence of neuropathy has been shown to increase with diabetes duration (King and Rewers, 1993). Furthermore, up to 26% of people with type 2 diabetes may have neuropathy at diagnosis (Young et al, 1993). Thus, screening for neuropathy is important at the time of diagnosis in this patient group.
Evidence would suggest that up to 15% of people with diabetic neuropathy develop an ulcer in their lifetime (Bild et al, 1989). Reducing ulcer occurrence is particularly important as foot ulcers precede non-traumatic lower limb amputations in 85% of cases (Pecararo et al, 1990). Once these lesions have occurred, their impact on patients and healthcare resources are significant. The estimated cost of treating a foot ulcer in the community was calculated to be approximately £3600 in 1997 (York Health Consortium, 1997) and a recent 2001 conservative estimate of costs for ulceration and amputation within the UK was £244 million (Shearer et al, 2003).
Thus, by using the appropriate screening tools to identify people with peripheral neuropathy, structured care pathways can be implemented to help reduce foot ulceration. A multidisciplinary team approach to provide suitable footcare education, footwear advice, annual chiropody, specialist podiatrist review, etc, has been shown to significantly reduce foot lesions (Malone et al, 1989; Boulton, 1995; Barth et al, 1991).
It is important to remember that neuropathy due to diabetes is symmetrical, which means it occurs in both feet and legs. Therefore, if neuropathy is found on one side only suspect other causes, such as lower back problems, e.g. sciatica.
There are some basic rules that need to be understood and followed every time a patient is examined:
- Always explain why and what you are doing, using language that is clear, precise and easy to understand, before you perform each test.
- Demonstrate each test on another area of the body where there is not likely to be any sensory loss, ensuring that the patient describes the sensation they perceive for each test.
- If there is any doubt about a response repeat the test several more times.
- When you have completed your testing make sure you share the results with the patient. This reinforces the concept of patient empowerment and self-care.
- The patient must be relaxed and in a warm environment.
- Following each test you must record your findings before starting the next one. Always repeat the test where negative results have been observed to verify their accuracy.
- It is important not to help, prompt or lead the patient’s responses.
- Demonstrating the inability to feel pain is a particularly powerful educational tool that is sometimes useful in motivating awareness and stimulating patient empowerment.
Simply by asking a patient if their feet are okay without examining them fails to grasp the significance of neuropathy. This approach also reinforces patient perception that feet are not important or at risk – a concept that when established is almost impossible to break.
Testing for neuropathy
There are several screening tools that are commonly used to detect neuropathy, some of which are expensive and time consuming while others are less so but may be more subjective.
Table 1 gives a list of perhaps the most commonly used tests in clinical practice. We have chosen to describe only three of the screening tools mentioned in Table 1: these are vibration perception, light pressure, and the neuropathy disability score. The reason for this decision is that these are perhaps the most reproducible and reliable methods to date (Young et al, 1993; Coppini et al, 1998; Smieja et al, 1999; Perkins et al, 2001). If only one method is to be used as an initial screening tool in a busy practice, we would advocate the 10g monofilament (see Figure 1), as it is quick, easy to use, cheap, reliable and reproducible (Smieja et al, 1999).
Light pressure
Not all 10g monofilaments generate 10g of linear pressure so it is important to obtain the most reliable ones. Also they do have a life expectancy and get fatigued if used repeatedly for long periods without allowing the nylon to rest (Booth and Young, 2000). Like all tools, it is only as good as the person using it, the quality of the monofilament, where it is used and how the results are interpreted. The best way to use a monofilament is given in Table 2.
Areas for testing
The literature is unclear about the definitive sites that must be tested for determining ulcer risk, ranging from 1–14 different sites on each foot (Perkins et al, 2001; Holewski et al, 1988). However, there are sites that are common to virtually all, namely the plantar surface of the metatarsal heads and the big toe (Figure 2). The rationale is that these sites most frequently ulcerate. At these sites areas of callus, induration, or scar tissue should be avoided.
There is no clear evidence on how many negative response sites equals an at-risk foot, however, some literature shows that even one site with a negative response (confirmed by several repetitions) on each foot may indicate an at-risk foot (Rith-Najarian, 1992; Birke and Rolfsen, 1998; Perkins et al, 2001), and clearly the more negative responses the greater the risk.
Thus, in summary, when considering screening in a busy clinical environment we would suggest the sites that should be tested are the plantar surfaces of the big toe and a minimum of three metatarsal heads. Neuropathy can be determined by the inability to detect one or more sites on each foot.
Vibration perception
This method of testing for nerve damage has been used for many years and, like the monofilament, it is relatively easily and reliable. A 128Hz tuning fork is cheap and widely available, however, a more quantitative method of assessing vibration perception is achieved by the use of a neurothesiometer (Horwell Scientific Laboratory Supplies, UK). Inability to feel vibration produced at 25 volts with this device has shown there to be a 7.7-fold risk of developing a foot ulcer (Young et al, 1993). This device is expensive and therefore may not be viable for use in routine screening clinics. A tuning fork, however, is simple and easier to use.
It is important to remember that vibration perception can decrease with age and other medical conditions, e.g. hypothyroidism and alcoholism. Table 3 suggests how to use a 128Hz tuning fork and this is demonstrated in Figure 3.
Neuropathy scoring systems
There are several established scoring systems that have been used to stratify neuropathy severity in people with diabetes, however they are perhaps too time consuming to use in routine clinical practice. Two methods are discussed here.
Neuropathy disability score (NDS)
NDS uses a neurotip, tuning fork, hot and cold rods and a tendon hammer (Young et al, 1993; Abbott et al, 2002). This simple assessment uses a system in which the patient scores one point for each incorrect test, and an extra point if the Achilles tendon reflexes are not determined with reinforcement (Table 4). The maximum score for each foot is five points, and a score of three or more out of 10 suggests neuropathy. In a study of more than 9000 patients, the NDS proved to be the best predictor of foot ulceration (Abbott et al, 2002).
Neuropathy symptom score (NSS)
Boulton et al developed a NSS which is widely accepted and commonly used to assess neuropathic symptoms (Boulton et al, 1998). Patients are questioned about the presence or absence and possible nocturnal exacerbation of muscular cramps, numbness, abnormal hot or cold sensations, tingling sensations, burning pain, aching pain, and irritation in the lower legs and feet from bedclothes (Table 5).
If the patient did not have a given symptom, then a score of zero was given. A score of one was given if the patient reported the symptom, and an additional score of one was given if the patient described nocturnal exacerbation. The summation of all symptom scores gave the NSS. An NSS of three or more was considered to be abnormal.
Autonomic and motor neuropathy
The clinical manifestations of autonomic and motor neuropathy are easy to recognise, whereas testing for them is more difficult and therefore is not usually undertaken in clinical practice. The clinical signs associated with autonomic neuropathy are:
- Dry skin due to the denervation of the sweat glands. These glands maintain skin moisture on the soles of the feet.
- Strong, easy-to-feel bounding foot pulses. Vasoconstriction is controlled by sympathetic nerve pathways. If these pathways are damaged, arteries lose vasomotor control and remain permanently dilated, being unable to constrict.
- Warm feet – this is due to the increase in skin blood-flow resulting from the above.
- Dilated dorsal veins – there are anastomoses between the arteries and veins, which are used in thermoregulation and are controlled by sympathetic nerve pathways. If these structures become denervated they remain open allowing the free passage of blood from the arteries directly into the veins.
- Postural hypotension – if arteries lose the ability to constrict gravity pulls the blood to the lower limbs. There is a sudden drop in proximal blood pressure, which may cause light-headedness or fainting due to a drop in cranial blood pressure.
The clinical signs of motor neuropathy are high arch feet, clawed toes and altered gait. Two things are important with high arched feet. Firstly, ask how long the patient has had high arches as they may be congenital or have developed early. Secondly, ensure that the arches remain high during weight bearing, as a non-weight-bearing foot that is hypermobile will often appear to have a high arch.
Ask how long the toes have been clawed and see whether they remain so on weight bearing. If the clawed toes are due to muscle wasting as a result of neuropathy you should be able to observe ‘hollowing out’ between the dorsal tendons.
Patients with altered gait typically show unsteadiness and a characteristically high-stepping gait similar to a drop foot gait.
Footcare protection following screening
Informing patients of the outcome of their foot examination is essential and provides a door of opportunity for foot health education, which should be simple, unambiguous and practical. Consistency is one of the keys to success. Thus, we would suggest that within each locality only one health education leaflet should be used by all healthcare professionals. Table 6 gives a rough guide of action to be undertaken following neurological assessment.
Conclusion
Being able to detect peripheral neuropathy in people with diabetes is probably the most important first step towards preventing neuropathic foot ulceration and lower limb amputations. Using the methods described above should allow for optimum detection. On their own, however, they become ineffectual unless supported by footcare protection systems. Although differences are clearly evident in methods used to detect ulcer risk due to neuropathy, there are several consensus documents that prove helpful and act as clear guides to practitioners, e.g. the International Working Group on the Diabetic Foot international consensus (www.iwgdf.org, accessed 22.02.05). Finally, foot screening should be viewed as a continuum, not a one-off occurrence – things change!
