Psychology is the discipline that attempts to understand the role of mental functions in individual and social behavior. In medicine, psychology became more widely integrated when the biopsychosocial model of disease was adopted by the World Health Organization, through the approval of the International Classification of Functioning, Disability and Health (ICF) (Figure 1) as the framework and classification of health.
In the biopsychosocial model, functioning and health results from a complex interplay of the health components - body functions and structures, activities and participation - and the contextual factors - environmental factors and personal factors [2]. In the ICF, psychological variables can be found either within the body functions or within the personal factors. Depression, as in the study by Brionez and coworkers [1], is part of the body functions (emotional function) - and as such can be the direct consequence of the health condition or an emotional reaction to the presence of the disease. The increased prevalence of depression in patients with inflammatory rheumatological diseases is partly attributed to a direct effect of cytokines, including IL-1, IL-6 and TNFα [3, 4]. On the other hand, helplessness or internality (beliefs about the controllability of a disease) [5] and coping (cognitive and behavioral strategies that persons develop when confronted with stressors) [6] are considered personal factors as they determine the individual psychological context through which a health condition can affect functioning and disability (including depression). The ICF framework also recognizes that the personal factors are not necessarily fixed, but can be influenced by aspects of health. The learned helplessness theory showed that the severity and unavoidability of a (health-related) stressor makes a vulnerable personality more likely to become helpless [7].
Brionez and colleagues admit that the cross-sectional design of the present study will not be able to unravel directionality or causality of the interplay between psychological variables and health [1]. Their analyses merely describe associations - nothing more, but also nothing less. The strength of this study is that not just one psychological variable but a broad range of psychological variables, each representing a different construct, were analyzed in one study. Each construct considered was shown to be independently important.
Remarkably, those psychological variables considered negative (depression, helplessness and passive coping) were associated with worse self-reported physical function, while positive beliefs (internality and active/adaptive coping) were not associated with better physical function. This observation contradicts the impression of rheumatologists that persons with ankylosing spondylitis adapt positively to their (slowly progressing) disease, and tend to underestimate the health impact of the disease. In clinimetric research, adaptation is seen as the major mechanism of a positive reference shift, which refers to the idea that patients do not rate their health in reference to an absolute standard but in reference to a relative standard that shifts over time [8]. The fact that active/adaptive coping in this study is not associated with better self-reported functioning does not exclude that a reference shift towards under-reporting takes place. It could be that a positive reference shift through adaptation is present but cannot be picked up by the instruments used in the study, or that adaptation is not the major determinant of a positive reference shift.