Illness beliefs regarding diabetic foot ulceration predict mortality

According to the self-regulatory model of illness (Leventhal et al, 1984), people form illness beliefs when faced with a threat to their health, and these beliefs play a central role in determining their emotional and behavioural responses to the illness. These illness beliefs centre around eight core issues that are hypothesised to interact with each other to form the overall illness schema (Table 1). The relationship between beliefs and outcomes is influenced by the nature of the disease in question; and, as such, specific beliefs or belief schema, are not universally associated with positive or adverse outcomes and are experienced differently from person to person.

Evidence suggests that patients’ illness beliefs may not only affect their emotional and behavioural responses to illness but may also influence clinical outcomes. For example, a recent review demonstrated that illness beliefs are associated with glycaemic control in diabetes (McSharry et al, 2011). Furthermore, a study comparing the effects of depression versus illness beliefs in predicting dietary, quality of life and glycaemic control outcomes in diabetes, showed that illness beliefs were more consistent and stronger determinants of these outcomes than depression (Hampson et al, 2000).Research has also shown that illness beliefs may predict mortality. Studies have shown that in groups of people with end-stage renal disease, death was more likely in people who believed their treatment was less effective (van Dijk et al, 2009; Chilcot et al, 2011).

The study
We sought to add to this literature by considering the role of illness beliefs in predicting mortality in people with type 1 or type 2 diabetes who have a diabetic foot ulcer. Furthermore, in view of the prominence of depression as a predictor of mortality in people with diabetic foot ulcers (Winkley et al, 2007; Winkley et al, 2012), we examined whether illness beliefs predicted mortality, after examining the role of potential demographic and clinical determinants and depression. For a full account of the study, see Vedhara et al (2016).

Patients were recruited into a longitudinal research programme examining psychological and behavioural aspects of diabetic foot ulceration and the study was approved by the North Somerset and South Bristol Research Ethics Committee. All participating patients provided written informed consent.

A total of 169 people with type 1 or type 2 diabetes and a neuropathic or neuroischaemic foot ulcer were recruited from outpatient podiatry clinics between January 2002 and January 2007. All clinics subscribed to a standard regimen of foot care and, at study entry, the following data were collected on all participants: age, gender, HbA_1c, number of previous ulcers, presence or absence of infection in the ulcer, diabetes type, presence of neuropathy and ischaemia, and ulcer size. Participants also completed self-report measures of illness beliefs related to their ulcers (Broadbent et al, 2006) and of depression (Zigmond and Snaith, 1983).

In November 2011, survival data were requested from GPs. This included whether they were deceased or alive on 1 November 2011 and, if they were deceased, their date of death.

Results
Of the 160 patients for whom data on mortality were available, 104 people were alive on 1 November 2011, 32 were deceased with date of death known, and 24 were deceased with date of death unknown.

The survival outcome was the number of days survived from the date of recruitment to 1 November 2011 or death from any cause. The analysis examining the data and predictors of mortality involved two steps. First, we considered all potential clinical and demographic predictors, as well as depression, in univariate analyses to identify the significant predictors. The results revealed that diabetes type (type 1 or type 2) and ischaemia were significant predictors of time to death.

In the second step, the measures of illness beliefs were added to these significant covariates. The analysis demonstrated that ischaemia remained a significant predictor of time to death (hazard ratio [HR], 0.976; P<0.0001). Identity beliefs (HR, 1.245; P=0.036) and coherence beliefs (HR, 0.775; P=0.036) also emerged as significant predictors.

Overall, people with less ischaemia, those who had a poor understanding of their condition, those who perceived they experienced more symptoms and those who had a greater belief in the effectiveness of treatment were most at risk of death compared with their respective counterparts. This is shown in Figure 1, which illustrates the average number of days survived based on a median split of patients’ identity beliefs. It demonstrates that, on average, people who believed they experienced a lot of symptoms survived 5.2 years, compared with 6.2 years for those who believed they experienced fewer symptoms.

Conclusion
We examined the role of illness beliefs in predicting time to death in people with diabetic foot ulcers. Our analysis showed that, even after controlling for other predictors, illness beliefs, ischaemia and coherence beliefs predicted time to death: people who believed they experienced a lot of symptoms were at increased risk of death. Death occurred more quickly in individuals with less ischaemia, who perceived their ulcers were associated with greater symptoms and had a poorer understanding of their condition.

The findings from our study could simply reflect the fact that people with diabetic foot ulcers with greater symptoms are experiencing a greater severity of the condition, which results in a greater risk of mortality. This is not, however, consistent with what is known about neuropathic and neuroischaemic foot ulcers. Nerve damage is a defining feature of such ulcers. Consequently, the more severe the underlying pathology, the more likely the patient will experience fewer symptoms. Thus, if we were considering a pathophysiological explanation alone, then the experience of fewer symptoms (an indication of more severe disease-state) might be associated with a faster time to death, rather than the converse.

The relationship between illness beliefs and mortality may be made clearer by examining the whole belief schema of an individual (i.e. the relationship between all eight core issues shown in Table 1). Patients who believed their ulcers were associated with greater symptoms (high identity beliefs) also believed that their ulcers had more serious consequences for them, and were associated with greater emotional distress and less personal control. This constellation of beliefs may have led to unhelpful behavioural and/or emotional responses, such as poorer adherence to treatment, leading to the observed association with mortality.

Illness beliefs can be modified and, in doing so, can result in improvements in a range of outcomes, such as treatment adherence and mood across many different conditions, including diabetes (Broadbent et al, 2009a; 2009b; Petrie et al, 2012; Jones et al, 2015). Therefore, taking illness beliefs into account during consultations may not only improve our understanding of the risk factors associated with mortality, but could also improve survival for people with diabetic foot ulceration.