Sunday, July 28, 2013
Diabetic Foot Assessment (a brief outline of a simple podiatric foot assessment)
Diabetes was recognized as a chronic, debilitating and costly disease by the United Nations in 2006. The World Health Organization has predicted the world population could double to 366 million by 2030. Something like, 47% of diabetics have some peripheral neuropathy and at a conservative estimate, 7.5% are suffering symptoms at the time of diagnosis. Research confirms early detection of the insensate limb is critical, but difficult because diabetic peripheral neuropathy (DPN) is often asymptomatic. Despite clear and authoritative clinical guidelines research supports first-line providers do not screen enough and their care quality suffers as a result. The purpose of this short presentation is to highlight the podiatrist role in screening the diabetic foot.
I am a firm believer the great maker, (whoever she was), was a podiatrist, or at least a friend of podiatry, for the longer we live the more we seem to rely on the services of others to tend to our feet. All the more critical as the bludgeoning diabetic population becomes endemic among the 45 plus age group.
For my sins, I am a community based podiatrist with a demographic made up of seniors, who are often: sight challenged hypertensive, peripherally ischaemic, venous return compromised, obese with ankle oedema, on anticoagulants, and suffering all manner of arthritides. High percentage are diabetic (and often not taking their medication), with chronic foot problems that limit mobility. Of course there are co-morbidities which collectively make toe nail clipping marginally safer than swimming blindfold slowly through a school of man eating sharks. However I suppose someone has to do it.
Aetiology of diabetic neuropathy is still poorly understood but glycation is probably a major factor. (The importance of glycaemia has been confirmed by studies showing incidence is greatly reduced by strict glycaemic control.) Resultant changes to vasculature also play an important part in causation of nerve damage. Disruption to neuronal integrity and failure to regenerate results in progressive neuropathy characteristically presents in a distal–proximal direction. Aging, duration of diabetes and poor glycaemic control all contribute to the presence of distal polyneuropathy.
The clinical conundrum:
Some present with acute sensory neuropathy i.e. severe polyneuropathic pain i.e. burning, hyperesthesiae, paresthesia, and dysesthesia [an unpleasant, abnormal sense of touch], but with minimal deficit. Symptoms include constant burning discomfort (especially in the feet), deep aching pain, with sudden, sharp, stabbing, or “electric shock” like sensations in the lower limbs. All these symptoms are prone to nocturnal exacerbation. Clinical examination is usually relatively normal, sometimes with allodynia on sensory testing; a normal motor exam, and occasionally reduced ankle reflexes.
Others more commonly present with chronic sensorimotor neuropathy and have a complete insensate foot and no symptoms. This neurological deficit may only be discovered during a routine neurological foot examination.
It is now recognized regular foot screening helps monitor and prevent serious complications in people coping with peripheral neuropathy and peripheral vascular disease.
Currently there is no gold standard for chairside assessment of Diabetic Peripheral Neuropathy (DPN). Conventional wisdom supports symptoms alone have relatively poor diagnostic accuracy and instead a combination of signs and symptoms approach is considered most appropriate. Symptoms may be primarily sensory, motor or both.
Simple composite examination scores are as accurate as complex examinations. Best evidence supports the use of the 10g monofilament combined with the modified Neuropathy Disability Score (NDS) helps chart protective sensation and identify those most likely to progress to ulcerative stage.
NDS is a score based on vibration perception, pin-prick sensation, temperature perception, and ankle (Achilles) reflexes.
Semmes-Weinstein monofilament examination (SWME) has become more widely used in testing protective sensation from the 1980s. Initially they were developed to assess neuropathy in Hansen’s disease. At a given pressure to the skin (10 grams) the nylon filament bends. The 5.07 (10g) filament is used to ascertain the level of protective sensation. With eyes closed three sites are tested i.e. the plantar aspects of the great toe, the third metatarsal, and fifth metatarsal (The Australian Diabetes Society). Research suggests people unable feel the monofilament have a 7.7-fold increase in ulceration risk. Monofilaments have high inter and intra examiner reliability and are generally considered effective, inexpensive and simple screening for ‘at risk’ feet.
The half -life of a Semmes-Weinstein monofilament is approximately 100 patients. Filaments fatigue and bend too easily, giving false positives after testing about 10 patients. They must be rested for 24 hours before regaining their firmness.
Diabetic peripheral neuropathy manifests with a wide variety of sensory, motor, and autonomic symptoms. Smaller fibres are usually affected first and with continued exposure to hyperglycemia, larger fibres become involved. The smallest sensory nerves are responsible respectively for thermal/burning pain (0.2-1.5 mu); and sharp pain (1-5 mu). Pin Prick sensation is tested with neurological pins. Altered thermal thresholds such as lowered heat-pain thresholds are associated with early changes in distal nerve segments and can be tested with simple heat/cold tests.
Bigger A-alpha (I) and A- beta (II) are responsible for propioception (13 -20 mu), vibration and pressure (6 -12 mu). Vibration Perception threshold is tested using a 128Hz tuning fork or Rydell Seiffer tuning fork. Vibration thresholds provided a strong indication of “risk” for future ulceration across a wide range of ages and durations of diabetes. (Neurothesiometer or Biothesiometer).
Deep tendon reflexes with neuropathy are commonly hypoactive or absent.
Motor problems include distal, proximal, or more focal weakness. Symptoms include weakness or atrophy of intrinsic foot muscles and associated foot deformities. Foot slapping and toe scuffing or frequent tripping may be reported. Proximal limb weakness include difficulty climbing up and down stairs, difficulty getting up from a seated or supine position, as well as falls due to the knees giving way. Strength testing - Examine for distal intrinsic extremity muscle atrophy, since weakness of small foot muscles may develop.
Autonomic neuropathy may involve the cardiovascular, gastrointestinal, and genitourinary systems and the sweat glands (sudomotor). People with generalized autonomic neuropathies may report ataxia, gait instability, or near syncope/syncope. Sudomotor neuropathy may produce heat intolerance, heavy head, neck, and trunk sweating with anhidrosis of lower trunk and extremities.
Claudication can be a useful symptom, but peripheral arterial disease (PAD) is commonly asymptomatic. Palpation of foot pulses is however a good simple test to determine the presence of peripheral arterial disease. The ankle-brachial pressure index (ABPI or ABI), using Doppler ultrasound is a useful adjunct to assess foot perfusion. Results can however be falsely elevated in the presence of arterial calcification and in this event clinicians are using photoplethysmography the measure toe-brachial pressure index or toe pressures.
A Foot Deformity Score helps identify high risk areas where repetitive trauma can cause breakdown, progressive ulceration, and infection. Screening includes signs such as: abnormal bony prominences, subluxation of the metatso-phalangeal joints, lesser toe deformities due to small muscle wasting, Pes Planus or Pes Valgus, previous amputation, and Charcot’s neuroarthropathy. About half all amputees experience a subsequent amputation of the other limb. Morbidity rates for limb amputees are poor with a life expectance of approximate five-years.
Dryness, tinea pedis, cracks, onychomycoses, acute erythema and tenderness, and fluctuance under calluses.
Inadequate footwear makes a significant contributory factor in causation of diabetic ulcers i.e. 35% -50% of cases. Shoes are made in standard sizes and feet are not symmetrical like shoes. Poorly fitting shoes cause sheer which may lead to secondary skin changes.
When shoes fail to support feet, high intermittent pressure result which puts the insensate foot at risk. A significant number of people wear shoes that do not fit their feet and research continues to shown poorly fitting shoes are more prevalent in the demographic with diabetic foot wounds than in those without wounds with or without peripheral neuropathy.
A routine foot assessment includes size, volume, suitability and wear marks of presenting footwear are reviewed and discussed with the patient.
There are several systems that categorize risk with the best known the University of Texas Diabetic Foot Risk System (with 7 categories). For simplicity however the demographic can be divided into four main divisions:
Low risk i.e. normal sensation and palpable pulses. Recommend an annual foot inspection with education.
Intermediate risk i.e. neuropathy or absent pulses or foot deformity. Recommend 3 to 6 monthly reviews.
High risk i.e. where two or more risk factors are present (neuropathy, peripheral arterial disease or foot deformity) and/or a previous history of foot ulcer/amputation have been recorded. Recommend 3 to 6 monthly reviews.
Critical Risk Recommend GP/Hospital referral within 24 hours.
Increased assessment frequency helps monitor rapidly-developing problems, such as ulcers, infections, gangrene, and Charcot’s neuroarthropathy. All of which need immediate intervention.
Until adequately assessed all Aboriginal and Torres Strait Islander people with diabetes are considered to be at high risk of developing foot complications and therefore will require foot checks at every clinical encounter and active follow-up.
Enhanced Primary Care Plan gives greater access to clients who are potentially at risk. Foot Health Education Programs promote daily self foot inspections with informed foot hygiene that minimize inadvertent self harm. Advice on appropriate foot gear and where to get it is combined with and open access in the case of emergency.
Despite clear and authoritative clinical guidelines research supports first-line providers do not screen enough and subsequently care quality suffers as a result. Early detection of the insensate limb is critical, but made all the more difficult because half our clients are asymptomatic. Evidenced based approach supports regular foot screening reviews combined with foot care and in conjunction with intensive glycaemic control improves Quality Adjusted Life Years. To this end effective care involves a partnership between patients and health care professionals.
I hope this presentation will convince you to use podiatry services to improve the quality of care to the diabetic population.
National Health and Medical Research Council (NHMRC) guidelines National Evidence-Based Guideline: Prevention, Identification and Management of Foot Complications in Diabetes (2005)
Australasian Podiatry Council