Abstract
The concept of sickness behavior offers a framework to view both the neurovegetative and psychological symptoms that accompany illness as a common entity that results from increased inflammatory activation. Despite the prevalence of sickness behavior in medical populations, to our knowledge this study provides the first attempt to develop a standardized measure to assess sickness behavior using standard self-report questionnaires commonly used with cancer patients. The set of items included in the measure match theoretical conceptualizations of sickness behavior and target symptoms that comprise anhedonia, depressed mood, cognitive dysfunction, social disinterest, fatigue, low libido, poor appetite, somnolence, sensitivity to pain, and malaise. The measure showed high internal consistency, adequate test-retest reliability, and good convergent validity with both psychological and biological correlates. A confirmatory factor analysis also determined that a two-factor, rather than a single-factor measurement model, encompassing a physical and a psychological sickness symptom dimension, accounted for sickness behavior. Future psychometric work is still needed to further validate this new practical assessment tool. Descriptive analyses revealed relatively low levels of sickness behavior symptoms in the sample as a whole with both physical and psychological sickness behavior symptoms exhibiting a significant linear decrease over time. As expected, both physical and psychological sickness behavior symptoms showed associations with two pro-inflammatory cytokine markers, IL6 and TNF-alpha and a neuroendocrine marker, cortisol. Longitudinal associations suggest that higher levels of the pro-inflammatory cytokine TNF-alpha may impact the progressive decline of physical sickness symptoms over time with symptoms taking longer to disappear. Because cortisol was associated with more rather than less physical sickness symptoms, results raise the question of whether the anti-inflammatory neuroendocrine activity may be dysregulated in breast cancer survivors. The mechanistic basis for these associations requires further examination. In this study it was also evaluated whether a cognitive behavioral stress management intervention and relaxation training intervention could reduce sickness symptoms over time. Breast cancer survivors were assessed at baseline and then randomly assigned to a 10-week cognitive behavioral stress management intervention (N = 70) or a 1-day control condition (N = 55). Psychosocial measures, urine, and blood were obtained from participants at 3 months, 6 months, and 12 months post-intervention to assess relevant behavioral, endocrine and immune variables. Relative to the control group, the experimental group showed marginally more prevalence of physical sickness behavior symptoms in the short term (post-intervention, 3-months; p = .08) and a steadier decline of symptoms in the long-term (15-month follow-up period). The adaptive nature of sickness behavior as a motivational strategy that helps restore homeostatic balance in the long run may be one possible interpretation of these results. Whether these intervention effects on sickness behavior were mediated by changes in pro-inflammatory cytokines or cortisol was examined but not supported by these data and needs to be further examined in future studies.