The structure and performance of the foot depend upon integrated function of all its tissues, including skin, soft tissues, bones and joints, supported by their neurovascular supply and the immune capability of the body. All these elements may become impaired in diabetes, and foot problems are correspondingly common. Many such problems are potentially avoidable and preventive foot care is an important element of the management of diabetes. The most common form of diabetic foot disease is that of chronic ulceration, although this may be combined with the symptoms and signs of either infection or ischemia from peripheral arterial disease. Ulceration has been estimated to affect up to 15% of all people with diabetes at some stage in their lives and the prevalence of active ulceration is of the order of 2.5%. The acute Charcot foot is an inflammatory disorder of the foot and is very much less common than ulceration – with the lifetime risk being usually said to be approximately 3 per thousand. It has been estimated that foot problems constitute the most expensive complication of diabetes.
Diabetic foot ulcers
The term “ulcer” refers to a break in the skin that is slow to heal. Even in specialist clinics, the overall rate of healing is about one third at 3 months and a half at 6 months, with only approximately two-thirds ever healing without surgery. The causes of chronic ulceration are multiple and break down into those that put the foot at risk (predisposition), those that lead to a break in the skin (precipitation) and those that inhibit healing (perpetuation). Ulcers are often multiple and recurrence is common: a person who is ulcer-free following a single episode has a 40% chance of having a new ulcer within 12 months.
The median age of onset is 65 years in industrialised nations, but lower in developing nations. Men are twice as likely to be affected as women. The incidence of ulceration is lower in Asians and in Blacks than it is in Caucasians, although this difference may be obscured by social factors and by varying access of ethnic minorities to effective primary health care in some countries and communities.
Predisposition to Ulceration
- neuropathy (especially by loss of protective sensation leading to traumatic injury), loss of autonomic innervation and reduced sweating may make the skin more dry and liable to ulceration
- peripheral arterial disease – either with dominant critical ischaemia or by the effects of chronic ischaemia with skin thinning and
- co-morbidity (poor vision, or by incapacitating illness such as previous stroke or heart failure with resultant abnormal pressure from bed rest)
The combined effect on the skin architecture of pre-existing peripheral arterial disease and neuropathy has been termed “pre-ulcerative skin”.
Precipitation of Ulceration
Ulceration requires the skin to be broken. The cause is usually an accident (such as acute trauma, unnoticed objects inside the shoe, badly fitting - or non-existent - footwear, or the result of abnormal forces. Infection is very rarely the cause of ulcers, but it often complicates them. Almost the only exception to this is tinea pedis – with its tendency to causes fissures between the toes which can act as a portal of entry for pathogenic bacteria.
The spectrum of predisposing factors varies from person to person, as well as from community to community. It is generally accepted that peripheral arterial disease is more prevalent in more industrialised countries, whereas neuropathy and infection are dominant factors in emerging nations.
Perpetuation of ulceration
Many factors may contribute to delayed healing. Although the extent of the contribution varies, they include
- bacterial infection
- reduced tissue nutrition from (a) occlusive arterial disease and (b) microvascular disease with abnormal delivery of oxygen and nutrients
- continuing trauma to the wound as result of loss of protective sensation
- hyperglycaemia with defective leucocyte function (likely but unproven)
In addition, the chronic wound develops its own biology, with the complex process of healing being said to be arrested in the phase of inflammation.
Prevention of Foot Ulceration
There are three interventions that may reduce the incidence of new ulceration and/or its impact.
- Education of the patient of the importance of foot disease
- Regular (annual) surveillance of all people with diabetes to establish whether they are at increased risk of ulceration through the presence of neuropathy, peripheral arterial disease or both.
- Ensuring that those at increased risk have access to long-term surveillance by an expert health care professional, who can institute specific preventive measures, such as the provision of appropriate footwear, or referral for consideration of revascularisation.
Despite these aims, there is currently no evidence to demonstrate that the institution of a specific care programme for those at increased risk is associated with reduced incidence of new foot disease – especially in those with previous ulceration, who are the group at highest risk. Further work is required to establish the structure of effective educational initiatives.
Presentation of Foot Ulceration
Although infection is only rarely a primary cause, its presence determines the severity of the presentation, and the immediate risk to the patient and their limb. Soft tissue infection is graded using the criteria of the Infectious Disease Society of America (IDS) and the International Working Group on the Diabetic Foot (IWGDF; International Diabetes Federation) into
- None – not clinically infected
- Mild – localised infection with any involvement and inflammation being confined skin and to a radius of 2cm or less from the wound margin
- Moderate – with any involvement being more deep or more extensive but without systemic symptoms or signs
- Severe – with symptoms and signs of a systemic inflammatory response syndrome.
Infection of the foot also divides into two broad categories: infection that involved soft tissue but not bone, and infection that involves bone (osteomyelitis).
Peripheral arterial disease
If there is significant peripheral arterial disease, there is more likely to be devitalised tissue, including gangrene. The skin is typically thinned and usually rather red, and there may be additional small scabs over pressure points – such as the dorsal aspect of the interphalangeal joints.
The so-called neuropathic ulcer tends to occur at points where the forces applied to the foot are particularly high, especially over the knuckles and under the tips of the toes, as well as under metatarsal heads. The skin is not thinned (as in cases of ischaemia), the pulses are often easily palpable and the ulcer itself may be surrounded by a rim of callus.
Some use the term “neuroischaemia” to emphasise the presence of both peripheral arterial disease and neuropathy. In practice, is ischaemia from peripheral arterial disease is very often associated with neuropathy because of dysfunction of the vasa nervorum.
Differential diagnosis: skin cancer
Although the likelihood of coincidental malignancy is small, it is essential that that the possibility is kept in mind. Clinicians should have a low threshold for undertaking a biopsy to exclude squamous carcinoma or melanoma.
Description and classification
Descriptions are used to provide details of individual lesions for the purposed of clinical communication, including clinical record-keeping. Classifications are used to define the characteristics of populations of ulcers – for the purposes of documenting outcome and comparing it with other centres. Various classifications have been proposed. These include
- Meggitt/Wagner – now generally outdated
- University of Texas – widely used and based on a 4x4 grid of depth plus the presence or not of infection and peripheral arterial disease
- PEDIS – based on the degree (variously graded) of peripheral arterial disease, area, depth, infection and neuropathy. It was designed for the purposes of prospective research – allowing the grades used to be specifically defined for individual studies.
- S(AD)SAD – includes the same measures as in PEDIS but each is graded 0 to 3
- SINBAD –was specifically designed to enable definition of ulcers of differing severity. Each of 6 criteria (as in PEDIS and S(AD)SAD plus the additional criterion of ulcer site: forefoot versus mid or hindfoot) is graded 0 or 1, and then summed. It has been shown that a score of 3 or more is associated with a worse outcome in widely different populations in different continents. The UT classification can be derived retrospectively from SINBAD, but not vice versa.
Prediction of Outcome
Various factors have been shown in different studies to be associated with/predictive of outcome in both univariate and multivariate analyses. [Which factors?]
Management of foot ulcers
The principles of management of foot ulcers are
- Prompt referral to a specialist team
- Formal assessment of ulcer and surrounding skin
- Debridement (i) sharp (ii) other) in order to remove surface debris and non-viable tissue:
- Treatment of clinically overt infection with systemic antibiotics
- Revascularisation if necessary and possible
- Cleansing and dressing of the wound to preserve a warm, moist environment for wound-healing and to protect the healing wound from trauma
- Provision of off-loading to protect the healing wound from the forces during ambulation
- Nutrition and self care
- Attempting to achieve optimal glycaemic control
- Continued close observation of the wound
Since the response to the above is frequently disappointing, many health care professionals resort to a variety of further remedies which may improve healing, but whose effectiveness, and cost-effectiveness, is not yet conclusively proven. These so-called “advanced wound therapies” may well have a place in management, at least of certain individuals and at certain times in the healing process but there are currently no agreed criteria for their use.
Long term care following treatment
People with a history of ulceration are those at greatest risk of new ulceration. Ideally, they should remain under specialist surveillance where this is available. It may be possible to reduce the incidence of new ulceration in this very high risk group through specific foot care, attention to footwear (orthoses) and self care advice, even though the evidence is currently lacking. Even if it is not possible to reduce ulcer incidence, the establishment of a system of surveillance that ensures ready access to expert professionals may enable prompt self-referral and this may lead to improved outcome of any new ulcer which does arise.
The main aspect of long term care lies in making every effort to reduce long term mortality (see below), and there is evidence that survival can be improved in this population by rigorous implementation of measures to reduce cardiovascular risk.
Morbidity and Suffering
The suffering that results from ulceration of the foot is considerable, and the extent of resultant depression is frequently neglected by professionals.
Depression can result from the prolonged immobility associated with the need to protect the foot, loss of income and self-esteem, the need for hospital admission, the impact of costs and fear of losing the limb. There has been no formal assessment of the benefit of assessing mood and the implementation of any therapy.
Disease of the foot is associated with reduced life expectancy. It has been shown that survival is reduced by an average of 14 years, and the mortality at 5 years has been shown to be 50%.
Some of the increase in mortality reflects the population affected by foot disease in diabetes, as well as the association with peripheral arterial disease (at least in industrialised countries. The available evidence suggests, however, that the high mortality is observed even in those who are relatively young at presentation, and is observed as much in those with neuropathic ulceration and absence of clinical evidence of peripheral arterial disease, as it is in those with established arteriosclerotic disease.
The effective study of the relative incidence foot disease in diabetes is dependent on there being community-wide data on the prevalence of diabetes itself. It may also be hampered by lack of systematic documentation in the incidence of ulcers, with the only information which may be available relating to hospital admissions for disease of the foot, including for amputation. It can, therefore, be difficult to assess the quality of care and to compare outcomes between different countries.
Within countries, however, and within single health care organisations – such as the NHS in the England and the Veterans Health Care Administration in the USA – there is evidence of geographical variation in the incidence of amputation that may be as high as ten-fold. While factors such as race and social deprivation may contribute to such variation, it is also thought that the training, experience and beliefs of the health care professional may make a significant contribution.
Health care costs
The full cost of foot ulcers is difficult to assess because it is borne by many different health care agencies, as well as by the patient and their family. In countries with a nationalised health service, the cost to the patient and their family can be enormous (data from Pakistan).
THE ACUTE CHARCOT FOOT
In 1868 Jean-Martin Charcot described the occurrence of inflammatory neuroarthropathy in joints of the spine, hips and knees in people with syphilis complicated by tabes dorsalis. The loss of deep pain sensation that occurs in this condition (or any other condition associated with loss of protective sensation, including diabetes) can rarely result in destruction of the structure of the joints and the resultant deformity can be gross. The condition was first described in the foot in 1881.
While there is a generally accepted hypothesis for the likely causes of the condition, it has not been proved. Similarly, the reason for the rarity of the condition (affecting only approximately 1% of all people with neuropathy) is not known, although various possibilities exist. The contralateral foot is affected (either at the same time or not) in approximately 20-25% cases. The median age of onset is in the late 50s and the occurrence of the condition is associated with a mean reduction in life expectancy of 14 years.
It I is not currently possible to identify those at especial risk and all that can be done is alert people whose diabetes is complicated by neuropathy to the existence of this rare condition. They should be told (and repeatedly re-told) that if ever they develop unexplained or worrying inflammation of the foot, with or without discomfort and/or deformity, they should minimise the weight bearing until the foot has been assessed by an expert.
Deformity of the foot may expose areas of skin to ulceration. When these occur, they may be complicated by infection. If the infection involves bone, it can be difficult to eradicate.
The mainstay of treatment lies in immobilisation – preferably in a non-removable fibreglass cast. The cast requires changing each 1-2 weeks (occasionally longer until the inflammation settles and the condition goes into remission. There is currently no evidence that any other intervention is effective. The time to remission varies in different case series but may be as long as 12 months or more. Residual deformity may require surgical correction.
THE FUTURE FOR FOOT CARE IN DIABETES
There is a clear need for more detailed information on the part played by different causative factors, and more evidence to establish the indications for specific therapeutic measures – in both chronic ulceration and in the acute Charcot foot. This can only be obtained by carefully conducted laboratory and clinical research. Until this information is available, the mainstay of management must rely on more widespread adherence to the principles of management listed above.
The management of disease of the foot should, however, be linked wherever possible to systems of measurement to document as far as possible both the incidence and the outcome of all new episodes within different communities. If it is possible to use the resultant information to demonstrate geographical differences, it will give further insight into pathways for optimal prevention and treatment.