Screening for diabetic foot ulcer in a primary care setting

Original article:
The North-West Diabetes Foot Care Study: incidence of, and risk factors for, new diabetic foot ulceration in a community-based patient cohort. Abbott CA, Carrington AL, Ashe H, Bath S, Every LC, Griffiths J, Hann AW, Hussein A, Jackson N, Johnson KE, Ryder CH, Torkington R, Van Ross ERE, Whalley AM, Widdows P, Williamson S, Boulton AJM. Diabetic Med 2002; 19: 377–84.

Summary
The North-West Diabetes Foot Care Study is a prospective analysis of a large (n = 9710) cohort of people with diabetes receiving community health care in north-west England. The aim of the study was to determine the incidence of foot ulcers and to study which screening methods are most effective for predicting diabetic foot complications.
Patients were mostly screened by their general practitioner or during a visit to a podiatry clinic. Demographic and specific foot risk data were collected at enrolment. After 2 years, a postal questionnaire was sent to all patients. In total, 7410 questionnaires were returned, some of which related to patients who were reported to have died or who had moved out of the area. The response rate to the questionnaire was 70%.
In 6613 patients, ulcers could be confirmed to have either developed or not developed. All positive ulcer reports were thoroughly crosschecked for validity. Also, a random control group of 300 negative ulcer reports was crosschecked. No false-positive or false-negative results were discovered. On the basis of these data, the annual incidence of foot ulceration was calculated to be 2.2%. Most ulcers were caused by footwear pressure (55%) or trauma (15%), while fissure, self-injury and other causes accounted for the rest. In a Cox proportional hazards analysis, several risk factors were independently related to new ulcer development (Table I).

Table I: Independent predictors of new diabetic foot ulceration using Cox’s proportional hazards multiple regression analysis.

The best predictors of diabetic foot ulceration in a primary health care setting are history of ulcer, abnormal disability score, visits to podiatry, insensitivity to 10 g monofilament, abnormal foot pulses, foot deformities and abnormal ankle reflex score.
Based on these data and previous research, the authors recommend the use of a neuropathy disability score, 10 g Semmes-Weinstein monofilament and palpation of foot pulses as screening tools in general practice.

Comment
This article highlights the need for large prospective studies of the risk factors for diabetic foot complications. Recent studies in this field have only included patients receiving specialized care or have been retrospective in design. Most have concerned patients in highly specialized tertiary care centres. This article, however, is one of the first to assess diabetic foot risk in a primary health care setting. Although there has been some prospective research in primary health care settings into other diabetic foot complications such as amputations [1], studies into the risk of diabetic foot ulcer are particularly scarce. Not only does the specific setting make this study special but also the huge number of patients enrolled.
The annual incidence of ulceration (2.2%) was substantially lower than that found in most other studies. The primary care setting is the most likely explanation for this, as most other studies have been in groups of patients at high risk. There are, however, some potential sources of selection bias that may have contributed to the low incidence. According to the study design, subjects were sent a postal questionnaire to assess the incidence of new ulcers 2 years after baseline screening. Even though the response rate was high (70%), 2300 subjects never replied, which is probably inevitable with such a large sample size. For various reasons the incidence of ulceration in this group may have been different. Subjects may have either found the questionnaire uninteresting or they may not have had time to answer it because they were too busy dealing with their diabetic foot complications. The authors reported a difference in ethnicity (more South Asians) and significantly younger age among the group of non-responders. The effect on the reported incidence is not known. Crosschecking the questionnaires revealed no false-positive or false-negative ulcer reports. There is, however, a theoretical chance of some false-negative reports, which would potentially lead to a higher incidence of foot ulcer.
In the article, the authors used a novel way to describe foot deformities. The Foot Deformity Score consists of the following dichotomous variables: small muscle wasting, hammer or claw toes, bony prominences, prominent metatarsal heads, Charcot arthropathy, limited joint mobility (prayer sign). If present, each deformity scored 1 on either foot. A total score of more than 3 was indicative of significant foot deformity. In the past, many studies of diabetic foot complications have tried to score deformities, but to my knowledge no semiquantitative instrument such as this has been used before. The Foot Deformity Score certainly has face validity and, in my view, the potential to be used in other clinical studies of diabetic foot risk.
The authors found that past or present ulcers were highly predictive of future ulceration. In most diabetic foot risk stratifications and classifications, patients with a history of foot ulcer are usually considered to be at high risk for diabetic foot complications [2]. In contrast with other studies, however, ipsi- or contralateral amputations were not significant factors in the multiple regression analysis [3]. The authors believe this to be confounded by ulcer history in this subset of patients. Another explanation might be that patients with a history of amputation have a high mortality rate [4]. They simply may not have been able to return the questionnaire.
The take-home message of this excellent article is that simple screening techniques to assess neuropathy using a monofilament and palpation of pedal arteries can identify patients at risk of foot ulceration, even in a primary health care setting. Hopefully these screening techniques will be widely applied — also by primary care physicians — to reduce the high burden of diabetic foot complications.

References
1. Rith-Najarian SJ, Stolusky T, Gohdes DM. Identifying diabetic patients at risk for lower extremity amputation in a primary health care setting. Diabetes Care 1992; 15(10): 1386–9.
2. International Working Group on the Diabetic Foot. Practical guidelines on the management and the prevention of the diabetic foot. Apelqvist J, Bakker K, Van Houtum WH et al., eds. Amsterdam: International Diabetes Fund, 1999; 4.
3. Peters EJ, Lavery LA. Effectiveness of the diabetic foot risk classification system of the International Working Group on the Diabetic Foot. Diabetes Care 2001; 24(8): 1442–7.
4. Van Houtum WH, Lavery LA. Outcomes associated with diabetes-related amputations in the Netherlands and in the state of California, USA. J Intern Med 1996; 240(4): 227–31.