Summary

Diabetes mellitus is a prevalent disease in our population. Diabetic foot is a distressing complication. Every family physician plays a significant role in its management. Clinical evaluation includes the assessment of nerve, vasculature, bacterial balance and the ulcer. Every office visit should be an opportunity for patient education, and family support system should be involved whenever possible.

摘要

糖尿病是本地常見的疾病。糖尿腳患更是令人悲痛的併發症。每位家庭醫生對它的診治都擔當著重要的角色。臨床評估包括對神經，血管，細菌量及潰瘍的檢查。每次病人到診都是對他們灌輸知識的好機會，同時在可能情形下向病人家庭作系統性的支援。

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Introduction

The management of common and important problems within our population is the cornerstone of being a Family Physician. It is estimated that around one-tenth of our population is suffering from diabetes mellitus, and at least one-tenth of the patients with diabetes mellitus are suffering from diabetes-associated foot problems. Up to fifty percent of lower limb amputation in diabetic patients could be prevented if proper education and regular assessment have been provided. A diabetic foot problem could be a combination of i) neuropathy, ii) vascular occlusion and iii) infection which predisposes the foot to develop ulcer. We will discuss these factors together with the assessment strategies in the following paragraphs one by one.

I) Neuropathy of the lower extremities in diabetic patient

Diabetic neuropathy is defined as a peripheral, somatic or autonomic nerve damage attributable solely to diabetes mellitus.¹

Clinical diabetic neuropathy means having an abnormal neurological examination finding performed by a physician skilled in the proper examination technique and that abnormal finding is consistent with nerve damage due to diabetes.

Confirmed diabetic neuropathy is defined as clinical diabetic neuropathy plus confirmation by abnormal quantitative neurological functional tests in two or more nerves.

Types of neuropathy

For the basis of clinical assessment, diabetic neuropathies are categorized into two main types:

1) Focal neuropathies (e.g. diabetic mononeuropathy) and

2) Diffuse neuropathies, which usually involve the limbs symmetrically and has glove-and-stocking distribution, and they are secondary to combination of vascular, metabolic and even autoimmune aberrations (e.g. distal symmetric polyneuropathy and autonomic neuropathy).

Clinical documentation of neuropathy

Clinical tests include:

• Sense of touch,
• Vibration sense,
• Position sense,
• Reflexes,
• Gait, and
• General examination of the foot.

For sense of touch, monofilament of different diameters are perpendicularly placed on different areas of each foot, except the callused areas. Each monofilament is to be placed for one to two seconds. The higher the number of the monofilaments, the more force is required to cause the skin to buckle.

The inability to sense a 5.07 monofilament with a 10 gm force, is consistent with severe sensory neuropathy and loss of protective sensation. Custom footwear should be worn in order to minimize mechanical trauma.

For vibration sense, a vibrating 128-Hz tuning fork is placed over the jaw to let the patient get familiarized with the vibrational sense. Then it is placed at the base of each great toe for at least ten seconds. The inability to feel the vibrating tuning fork is considered to be a large nerve fibre loss, and it carries the same significance of inability to sense a 5.07 monofilament.²

Position sense, which is a large nerve function, is typically preserved until the late stages of distal symmetric polyneuropathy of diabetes. To test this, with the patient's eyes closed, the big toe is to be firmly grasped by the examiner. The toe is then wiggled up and down, and he/she is asked to identify the position of the great toe.

Testing the deep tendon reflexes provides information of the large motor nerves. The responses are usually classified as present, present with reinforcement, or absent.³

It should be noted that in distal symmetric polyneuropathy, the lower extremities are more often involved than the upper extremities. Otherwise, alternative neuropathic aetiologies should be sorted out.

To observe his/her gait, he/she will be asked to walk a straight line with heel to toe, paying particular attention to the foot movements. In the case of advanced distal symmetric polyneuropathy, due to defective propioception, the feet will be lifted unnecessarily high, and he/she may slap the floor.⁴

General examination of the feet for calluses and corns, dryness and fissures can provide evidence of defective proprioception and autonomic neuropathy respectively. Structural deformities such as hammer toes and claw toes, which are due to muscles imbalance, should be documented.

Management

Management of distal symmetric polyneuropathy includes:

• Treatment of risk factors,
• Treatment for painful neuropathy, and
• Early detection and hence prevention of further complications from neuropathy.

At present there is no treatment that will reverse the neuropathy already present, but controlling risk factors could delay its onset or slow down the progression. The DCCT and the UKPDS studies have demonstrated conclusively that better glucose control can prevent or slow the progression of diabetic neuropathy.^5-7

Although only treatment of hyperglycaemia has been proven to prevent or slow the progression of diabetic neuropathy, it is felt that it is also important to manage risk factors such as hypertension, elevated cholesterol and smoking.

For treatment of painful neuropathy, the initial step is to determine whether the pain is actually secondary to other cause(s), such as peripheral vascular disease.⁸ Once it is determined that the pain is secondary to distal symmetric polyneuropathy, it is classified into acute or chronic painful neuropathy.

Acute painful neuropathy usually has onset within three years from the diagnosis of diabetes, and it lasts for less than twelve months. It is self-limiting and the patient often responds well to non-steroidal anti-inflammatory drugs.

Chronic painful diabetic neuropathy has gradual onset within eight to twelve years from the diagnosis of diabetes. It lasts longer and for more than twelve months, and the pain gets worse on progression. Once the structural nerve function deteriorates to the point that sensation decreases below the pain threshold, the pain may get "improved".

Chronic painful diabetic neuropathy can be further classified into 1) dysesthesia, 2) paresthesia and 3) muscle pain.

1) Dysesthesia pain is described as "painful burning sensation when something touches my foot". It is treated by a medication called Gabapentin.

2) Paraesthesia pain is described as "pins and needles-like sensation over my foot". Carbamazepine given initially at 100 mg twice a day up to 400 mg three times a day for a six-week period, or Phenytoin at 100 mg three times a day up to 200 mg three times a day are the recommended regimens.

3) Muscle pain is described as "night cramping, band-like sensation at the leg". The patient should be encouraged to have more exercise, while the pain itself can be treated by analgesics.

In order to prevent further complications of diabetic neuropathy, routine assessment of the feet by health care professionals, advice on proper footwear and patient education are important.

At each office visit the Family Physician should examine the patient's feet looking for the presence of foot deformity, callosity, ulcer, signs of autonomic neuropathy like skin fissure and signs of peripheral vascular disease. Assessment of sensory neuropathy should be performed at least once a year. For assessment of sensory neuropathy, monofilament and vibration fork are the recommended tests.

If there is any sign suggestive of loss of protective sensation, he/she should wear proper footwear.

Objectives of the footwear are:

1) To relieve areas of excessive plantar pressure,

2) Reducing shock and

3) Reducing shearing stress to the soft tissue.

Each patient should be educated to avoid foot soaks, hot pads and self-treatment of callosity. He/she should dry the feet carefully after showering, particularly the toe webs area. He/she should inspect his/her feet everyday. An unbreakable mirror can enable him/her to inspect the plantar surface.

II) Diabetic peripheral arterial disease

Clinical diagnosis

Typically, a patient might present initially with intermittent claudication. It occurs in situations where a increased muscular activity and increased blood flow is required.

Calf claudication points to femoral or popliteal arterial stenosis, while thigh and buttock claudication indicates iliac or even aortoiliac arterial stenosis.

Rest pain is typically located at the distal forefoot. The pain starts around an hour after lying supine, which predisposes inadequate blood flowing from the ankle level to the toes against the gravity, and the pain subsides gradually upon dangling of the foot.

Unfortunately, due to peripheral neuropathy, many diabetic patients would not be able to feel the pain even when the disease has progressed.

Upon physical examination, the foot is pale on elevation (pallor on elevation) to more than 45^o while it becomes pink when the foot is let down in a dependent position (dependent rubor). Also, at the supine position, when a pressure is applied to the skin and then the pressure is abruptly removed, the timing for the foot to recover its original colour is noted. It is abnormal whenever it takes more than five seconds for the pallor to reappear to its usual skin colour (capillary refill time).

Venous refill time is checked by having the leg elevated in supine position to a 45^o inclination for one minute, followed by asking the patient to sit upright and put his/her leg down dangling over the side of the examination couch. It is considered abnormal if it takes more than 20 seconds for the vein to bulge again.

Palpation of the peripheral pulses at the femoral, popliteal, and pedal (dorsalis pedis and posterior tibialis) sites should be graded as normal, diminished or absent. The presence of skin atrophy, hair loss or ulcer indicates a progressive peripheral arterial disease as well.

Presence of femoral bruit indicates around 50% of arterial stenosis and the bruit may disappear altogether when there is more than 90% of stenosis.

Non-invasive investigation

Ankle brachial index (ABI), is a ratio which indicates the ankle arterial pressure in reference to the brachial arterial pressure.

In general, there are four clinical indications when it should be measured.⁹

1) Exercise-induced calf pain,

2) Sign of critical ischaemia such as skin atrophy,

3) Suspected diminished pedal pulse(s) on palpation, and/or

4) Femoral bruit on auscultation.

Although the clinical examination of all the aforementioned specific clinical features might not be demonstrated in every office consultation, these signs should be specifically looked for at least once a year as an annual clinical checkup.

When the ABI is greater than 0.9, it should be measured at least once in two years. When it is between 0.5 and 0.9, it should be measured at least once in three months. Whenever it is less than 0.5, the foot is in critical ischaemia. Referral to a vascular specialist should be commenced as early as possible.

Invasive investigation of peripheral arterial disease

As mentioned, when the lower limb has suggestion of having clinically significant peripheral arterial stenosis, the patient should be referred to a vascular surgeon as early as possible.

Angiography with contrast is still the "gold standard" for assessment of the diabetic patient with peripheral vascular disease. Due to advances in technology, traditional film screen angiography has been replaced by digital subtraction angiography (DSA).¹⁰ It can achieve the optimum visualization of the symptomatic vessels, maximize the guidance for minimally invasive therapy and use the least amount of contrast.

Special consideration must be given to those patients on metformin. Metformin is recommended to stop at least one day before the examination. It can be resumed around 48 hours after the procedure, provided the serum creatinine level is less than 150 mmmol/l.

III) Diabetic foot ulcer

There are three main aetiological factors for diabetic foot ulcers: 1) pressure, 2) circulation and 3) infection. Optimal management of the ulcer(s) includes optimization of all these three factors, as well as the management of the general medical conditions.

Ulcer healing is the goal. Even when ulcer healing could not be achieved, maintaining bacterial balance, preventing systemic complication, maintaining the quality of life and addressing the underlying fears of the patient ought to be provided as far as we could.

Initial assessment

Before managing the wound of a diabetic patient with foot ulcer(s), four healing enhancing factors should be looked for:

1) Pressure off-loading over the wound and the surrounding area,

2) Adequate vasculature to heal,

3) Bacterial balance in the wound, and

4) Ability to heal in terms of optimization of diabetic control and presence of coexisting medical conditions.¹¹

1) Pressure

Neurotropic pressure-induced ulcers develop over pressure points on the plantar side of the foot, especially over the metatarsal head(s), the great toe, the heel and any bony prominence. An ulcer starts with a callosity of the stratum corneum, followed by local haemorrhage, blistering and then skin breakdown, resulting in an ulcer, which is a complete loss of epidermis.

Therefore, pressure off-loading is essential for ulcer healing. Methods of pressure off-loading include aggressive debridement of callosity and appropriate deep-toe shoes.

2) Circulation

When a pedal pulse is palpable upon a clinical examination, the pressure is estimated to be around 80 mmHg. The Doppler ankle-brachial index (ABI), as aforementioned, is commonly used to diagnose arterial disease. A ratio of 0.9 or above indicates the absence of a significant arterial disease, while a ratio of 0.5 or below indicates a severe arterial occlusion.

Concerning the surgical management, balloon dilation or Percutaneous Transluminal Angioplasty) (PTA), and vascular bypass are the surgical options, although these might not be beneficial in case of extensive distal arterial disease.

3) Infection

The longer the ulcer is present, the higher chance that the surrounding tissue will get an increased bacterial load.¹² As the bacteria compete within the wound for oxygen and nutrients, it will significantly delay the healing.¹³

Clinical signs of infections include:

• Increase in amount of discharge,
• Purulent discharge,
• Discharge with malodour from the ulcer, and
• Erythema or oedema of the surrounding tissue.

Due to peripheral neuropathy, presence of pain is not a reliable sign.

Surface bacterial cultures of the wound usually could not represent the organisms within the underlying granulation tissue of the wound. Ideally, the gold standard for bacterial culture is a tissue biopsy, but it is not practical to do it for every ulcer. Balancing between these two culturing methods, a proper culture should be taken after removal of the debris, the deep portion of the ulcer base should be sampled, but accumulation of pus should be avoided.

If an ulcer invades into bone, there will be a high chance of osteomyelitis, particularly if the erythema surrounds the ulcer extends to more than 2 cm size, and there is worsening of diabetic control, fever or any signs of bacteraemia.¹⁴ Early referral to a specialist is important for limb salvage. It should be noted that the initial X-ray of osteomyelitis is usually negative.

4) Diabetes control and general health

If the HbA1c is 12% or above, there will be an impairment of the host response to withstand an infection. Smoking, coexisting hypertension can directly impair the ulcer healing.

Assessment of a diabetic foot ulcer

The five components are 1) size and location, 2) ulcer base, 3) the margin and 4) assessment of the pain:

1) Size and location
The location of the ulcer should be mapped out on a foot diagram. The depth should be probed so as to detect any undermining or sinus.

2) Ulcer base
Different colours of the base indicate different stages of inflammation.

• Black devitalized tissue (eschar) may either be soft or firm and it should be removed immediately.
• Yellow fibrous base can be sloughy or firm, indicating infection of the deep tissues, immature granulation or lack of vascular supply. When it turns darker, or malodorous, there is an increased bacterial load inside the granulation tissue, indicating need for early removal of this infected granulation tissue.
• When the granulation tissue is salmon pink, firm and moist, it is healthy and it gets adequate vascular supply.

3) Margin
If there is excess moisture, maceration of keratin, oedema, erythema and increased warmth around the wound margin, ongoing infection should be considered. Also, callus around the wound margin should be particularly looked for.

4) Assessment of the pain
The neuropathic diabetic foot is usually painless, and whenever pain occurs it should be documented in terms of self-report. The 10 cm visual analogue scale is used for quantitative pain assessment.¹⁵ He/She is asked to grade the pain by marking along the 10 cm scale, with 0 cm meaning no pain and 10 cm indicating the worst pain that has experienced. The presence of any new pain or increase in pain indicates vascular compromise and infection.

Management of the ulcer

It includes 1) debridement, 2) wound cleansing and irrigation, 3) use of antibacterial agents, and 4) dressings:

1) Debridement

Because diabetic foot ulcers are chronic and non-healing, it has been demonstrated that aggressive, ongoing surgical debridement converts a chronic non-healing ulcer into an acute, healing wound.¹⁶ Sometimes the wound assessment could only be completed after debridement of the necrotic tissue.

Method of debridement is a spectrum, ranging from flushing away debris with low-pressure irrigation to wide excision of necrotic tissues.

Concerning the methods, sharp surgical debridement is the commonest method. The hyperkeratotic rim and ulcer base must be debrided down to the level of active bleeding.

Presence of haemorrhage after surgical debridement is a desirable sign as it indicates a viable ulcer base. To prevent collection of a local haematoma, the bleeding is contained by local pressure together with a local application of calcium alginate or absorbable gelatin sponge such as Gelfoam.

All the overhanging edges should be debrided. All sinuses should be opened or marsupialized to allow healing from the edges. Exposed bone requires local surgical removal of the infected focus.

After the debridement, calcium alginates or moist gauze should be left in place for around one day, in order to stimulate initial healing. Then the wound can be cleaned.

2) Wound cleansing and irrigation

Wound cleansing and irrigation can be performed simultaneously with debridement. Saline is the chosen solution. It includes pouring the saline over the wound (but not soaking the wound) and/or irrigating the ulcer with the solution through a syringe at a pressure of around 5 psi by using a 30 mL syringe and 18-20-gauge angiocatheter.

It should be noted that foot-soaking will enhance tissue maceration and hence bacterial entry. Moreover, the pressure of irrigation should not be higher than 15 psi in order to prevent tissue destruction.¹⁷

3) Use of antibacterial agents

Whenever there is a sign of osteomyelitis or cellulitis, systemic antibiotics should be commenced. However, it should be noted that use of topical antibacterials may increase the emergence of bacterial resistance.

4) Dressings

An ideal dressing can

a)  Remove excess exudates and toxic components,
b)  Maintain a high humidity at wound/dressing interface,
c) Allow gaseous exchange,
d) Provide thermal insulation,
e) Afford protection from secondary infection,
f) Be free from toxic contaminants and
g) Allow removal without trauma at dressing change.

Concerning the choice of dressings, conventional dressings such as gauze, non-adherent gauze, impregnated gauze and packing strips are commonly used. They are absorbent, effective for packing sinus tracts and tunnel areas. They can prevent premature wound contraction and they are readily available.

Advanced dressing includes alginates, films, foams, hydrocolloids and hygrogels etc. They can provide an ideal moist wound environment by absorbing exudates (alginates, foams and hydrocolloids) or maintaining moisture (hydrogels).¹⁹

However, dressings of a occlusive nature (restriction of water vapour and gases exchanges), such as hydrocolloids and films, should be discouraged as the occlusive environment can become a breeding ground for bacteria.²⁰

Moreover, other factors such as user friendliness and cost effectiveness should be considered in the use of advanced dressings.

Conclusion

Diabetic foot problem is a challenge for both patients and health care providers. A professional team approach is necessary. On the other hand, patient education must be an integral part of the care. The regimens of self-management include proper foot inspection and care, as well as acknowledgement of symptoms or signs that require an early approach to get to a health provider. Finally, every office visit should be an opportunity for self-management education, and family and support systems should be included whenever possible.

Key messages

1. Up to half of the lower limb amputation in diabetic patients could be prevented if proper education and regular assessment had been provided.
2. Diabetic foot is a combination of neuropathy, vascular occlusion and infection. They predispose the foot to develop an ulcer.
3. Inability to sense a 5.07 monofilament, at 10 gm force, is consistent with severe sensory neuropathy and loss of protective sensation.
4. Inability to feel a vibrating 128Hz tuning fork is consistent with a large nerve fiber loss.
5. An optimized blood sugar level can prevent the progression of a diabetic neuropathy.
6. Pallor on elevation, dependent rubor, capillary refill time, venous refill time and diminished peripheral pulses are significant signs of vascular occlusion.
7. When the value of an ankle-brachial-index is less than 0.5, the foot is in critical ischaemia.
8. Initial assessment of a diabetic ulcer includes pressure over the wound, vasculature, bacterial balance and blood sugar level.
9. Further assessment and management of an ulcer requires debridement, wound irrigation and proper use of dressings.
10. Ongoing surgical debridement can convert a chronic non-healing ulcer into an acute healing ulcer.

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References