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Diabetic foot care

Consultant physician Dr Darryl Meeking gives GPs essential advice on managing foot problems in diabetes patients

What causes diabetic foot ulceration?

This is caused by a combination of some or all of three major risk factors: abnormal foot shape, nerve damage (neuropathy) and impairment of blood supply.

Deformities in the diabetic foot may be due in part to a limitation of joint mobility due to abnormal glycosylation of connective tissue. Charcot deformities, nail abnormalities, peripheral oedema and deformities secondary to surgical procedures also increase the risk of foot ulceration.

The most common risk factor for the

development of foot ulceration is chronic sensorimotor neuropathy. This may occur with or without symptoms (painful or painless). It is more common with increasing

duration of diabetes and poor glycaemic control.

How should GPs assess feet in diabetes patients?

Diabetic feet should be examined at least

annually. Early clinical signs of sensory

neuropathy include decreased vibration sense, absent ankle reflexes and muscle wasting. There are a number of different methods for evaluating and scoring signs of diabetic neuropathy. The classical tools used are tendon hammer, pin, cotton-wool swab and 128Hz tuning fork. A validated technique for assessing pressure sensation is the application of a 10g monofilament to the skin.

These allow an assessment of reflexes, pain, light touch, vibration and temperature sensation. NICE recommends the use of a calibrated tuning fork or a 10g monofilament for assessing sensation. The feet should be assessed for sensory loss in multiple sites, concentrating on the tips of the toes and soles of the feet.

Feet should be inspected for foot deformities, dryness and fissuring of the skin. Cracks in the skin provide an entry site for secondary infection, particularly in the

inter-digital spaces.

Pedal and posterior pulses should be palpated. The absence of palpable peripheral pulses is the typical finding and signifies the potential existence of large vessel disease.

How should the at-risk foot be managed?

Feet with evidence of neuropathy, absent pulses or deformity are at risk. Patients

with at-risk feet should be encouraged to

inspect them daily and report any lesions early to a health care professional. Dry

feet should be lubricated three times daily with a simple moisturising cream. Callus should be gently rubbed away using a pumice stone. Nails should be clipped

regularly. Footwear should not be slip-on and soft insoles should be inserted. The uppers should be soft and the toe-box broad and deep. Patients with foot deformities may require orthotic input for appropriate footwear and if severe be referred for orthopaedic correction.

How is foot ulceration managed?

It is vital that patients with active foot

ulceration receive input from a specialist

podiatrist.

The characteristic complication of the neuropathic foot is the neuropathic ulcer. This is positioned most commonly on the tip of a toe or underneath a metatarsal head. It can also be found on the dorsum of the toe, between toes or underneath the heel. Its appearance is typically 'punched out' with surrounding callus formation. It is typically painless but may penetrate to involve deeper tissues, including bone.

In the initial stages of acute foot ulceration it is important to reduce weight-bearing. This is essential to promote healing. Casting techniques offer an alternative to bed rest since they allow the patient to retain mobility. The traditional cast is the total contact plaster cast with simple padding. Removable casts such as the Scotch-cast boot are being increasingly used, but removable cast walkers such as the Aircast pneumatic diabetic walking boot have superseded the use of Scotch-cast boots in many centres. Pressure can also be reduced with foam insoles moulded to the plantar surface of the foot.

A foot ulcer is surrounded by callus and this needs to be surgically removed. This

has the effect of reducing local pressure,

allowing effective drainage of the wound and enabling re-epithelialisation of the

ulcer edges. This should be carried out

only by a specialist podiatrist or trained

surgeon.

Antibiotic therapy is necessary for infected ulcers. High-dose, broad-spectrum agents should be used pending further information about organism sensitivities from wound swab cultures. Infected ulcers that exhibit more than a 2cm surrounding rim of erythema or that penetrate deep require intravenous antibiotic therapy.

How should the ischaemic foot be managed?

Intermittent claudication and rest pain may be presenting symptoms of major vessel

disease. Ulceration is also a common

feature of the neuro-ischaemic foot. Its

appearance is different to that of the

neuropathic ulcer, having a predilection for lateral foot margins and distal toes. Minor trauma is often the precipitating factor for tissue damage.

Unlike neuropathic ulceration, ischaemic ulceration is frequently painful. This can sometimes be successfully treated with simple or codeine-based therapy but frequently only responds to regular opioid analgesia. Ulcers should be cleaned with a sterile saline solution. Only sterile, non-adherent dressings should be applied to the cleansed wound.

Patients with ulcers and evidence of poor foot perfusion should be referred to vascular surgeons for assessment. The increased emphasis on limb salvage and the development of new techniques of re-vascularisation has led to a reduction in the frequency of major amputation.

How should Charcot's disease be managed?

Acute Charcot foot (neuro-arthropathy) is a progressive but self-limiting condition. It

occurs in those with peripheral neuropathy and a good vascular supply. The patient

frequently presents with a hot, swollen

foot that may be painful. The typical site

is the tarsal-metatarsal region or the metatarso-phalangeal joints. The ankle may also be affected.

As the disease progresses the structure of the foot is destroyed. Joint dislocations and fractures occur. These are often in the mid-foot, leading to the collapse of the arch. This can result in a 'rocker bottom deformity' because of displacement and subluxation of the tarsus or medial convexity relating to the talo-navicular joint or tarso-metatarsal dislocation.

The key to treatment, and long-term preservation of the limb, is immobilisation. This will prevent further joint damage and should be recommended immediately. Options for immobilisation include crutches, wheelchair, total contact cast and replaceable cast walker.

Deformity will subsequently predispose the affected foot to ulceration and infection.

How should GPs manage neuropathic pain?

Tricyclic drugs are useful for many patients with neuropathic pain. Imipramine is beneficial in 60 per cent. The initial starting dose of 25-50mg is increased to a maximum of 150mg. Amitriptyline is an effective alternative with a similar dosing schedule.

Gabapentin (titrated to 600mg tds) and its more recent successor pregabalin (titrated to 300mg bd) are licensed as oral agents for use in painful neuropathy. Common side-

effects are dizziness and drowsiness.

Carbamazepine and phenytoin have been used in the treatment of neuropathic pain but side-effects are common and these drugs are now used less frequently.

Opiate-based therapies cause a degree of dependence but may be advocated in severe intractable cases. Tramadol is a centrally acting opioid derivative that is less addictive.

For superficial discomfort and pain (burning or tingling) capsaicin cream (0.075 per cent), derived from the chilli pepper, can be used. This is applied three to four times daily to symptomatic areas of the foot.

Most of these treatment regimes, with the exception of pregabalin, need to be continued for several weeks to achieve benefit.

Spinal cord stimulation TENS machines may be beneficial in some – particularly in those patients with pain localised to one limb only.

Darryl Meeking is a consultant physician specialising in diabetes and endocrinology at Queen Alexandra Hospital, Portsmouth. He is also an honorary clinical lecturer at the University of Portsmouth and honorary senior lecturer at the University of Southampton. He has a special interest in diabetic foot services.

Competing interests None declared

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