Longitudinal relationship between onset of physical symptoms and functional impairment

Patients with chronic physical symptoms (e.g., chronic pain) often have significant functional impairment (i.e., disability). The fear avoidance model is the dominant theoretical model of how the relationship between chronic physical symptoms and functional impairment develops and proposes a cyclical/bidirectional relationship. There has never been a definitive test of the proposed bi-directional relationship. The current study followed 767 Operation Enduring Freedom/Operation Iraqi Freedom soldiers from pre-deployment, when they were relatively healthy, to one year after deployment, when it was anticipated that symptoms would increase or develop. Over the four assessment time points, physical symptom severity consistently predicted worse functional impairment at the subsequent time point. Functional impairment did not show a consistent relationship with worsening of physical symptom severity. These findings suggest that changes to functional impairment do not have a short-term impact on physical symptom severity. Keyword: disability, health function, chronic pain, medically unexplained symptoms, Iraq, Veteran, fear avoidance model, health status, fatigue PHYSICAL SYMPTOMS AND HEALTH FUNCTION Longitudinal relationship between physical symptom severity and functional impairment Patients with chronic physical symptoms (e.g., chronic pain) often have significant functional impairment (i.e., disability or limitations in the ability to perform daily and social activities). Cross-sectional studies find that physical symptoms and functional impairment have a strong association. For example, a cross-sectional study of physical symptoms and functional impairment found each accounted for 35% of the variance in the other (Kroenke et al., 1994). This relationship is significant when controlling for mental health variables (e.g., depression, PTSD; (Helmer et al., 2009; Jackson et al., 2006; Tomenson et al., 2013)) and among patients with medically unexplained symptoms/illnesses (Hoffman & Dukes, 2008) and medically explained symptoms/illnesses (Sogutlu, Levenson, McClish, Rosef, & Smith, 2011) leading some to conclude that chronic physical symptoms and functional impairment are inextricably linked. The fear avoidance model, a cognitive behavioral model, is the dominant theoretical model of the relationship between chronic physical symptoms and functional impairment and has guided our understanding of this relationship for the past three decades (Lethem, Slade, Troup, & Bentley, 1983). The fear avoidance model proposes a cyclical/bidirectional relationship between physical symptoms and functional impairment (Crombez, Eccleston, Van Damme, Vlaeyen, & Karoly, 2012; Wideman et al., 2013). Specifically, according to the model, acute physical symptoms are hypothesized to trigger pain catastrophizing (a cognitive error in which there is exaggeration of the consequences of an event) which causes fear and avoidance of activity. Avoidance of activity leads to physical deconditioning and functional impairment. Functional impairment (and associated physical deconditioning) then increases the severity of the physical symptoms. The fear avoidance model is also the basis for the dominant behavioral treatment for PHYSICAL SYMPTOMS AND HEALTH FUNCTION chronic physical symptoms, cognitive behavioral therapy (Wideman et al., 2013). In cognitive behavioral therapy, patients are encouraged to challenge catastrophizing beliefs and to slowly increase activity to reduce physical symptoms and functional impairment (Brown, 2004; Castell, Kazantzis, & Moss‐Morris, 2011). Recently, however, there have been questions about the directionality and cyclical nature of the fear avoidance model (Wideman et al., 2013). Studies on the direction of the relationships between variables within the fear avoidance model suggest that common assumptions may be incorrect (Sullivan et al., 2009; Wideman & Sullivan, 2011). For example, two recent prospective studies failed to find that pain catastrophizing precedes fear of activity (Bergbom, Boersma, & Linton, 2012; Wideman, Adams, & Sullivan, 2009). The cyclical relationship between physical symptoms and functional impairment is a foundational assumption of the fear avoidance model, yet there has not been a study that examines this bidirectional relationship. There studies that examine one direction of this relationship. These studies find longitudinal evidence that physical symptoms lead to increases in the severity of functional impairment (Momsen, Jensen, Nielsen, & Jensen, 2014; Tomenson et al., 2013). There is conflicting evidence, however, that functional impairment leads to increases in the severity of physical symptoms. Two prospective studies found that functional impairment was associated with greater physical symptoms over time (Bergbom et al., 2012; Bergman, Jacobsson, Herrström, & Petersson, 2004) while two reviews found limited evidence that physical deconditioning increases physical symptoms (Smeets et al., 2006; Verbunt et al., 2003). In the fear avoidance model physical deconditioning is proposed to explain the relationship between functional impairment and physical symptoms. PHYSICAL SYMPTOMS AND HEALTH FUNCTION The goal of the current study is to examine the prospective bidirectional (cross-lagged) relationship between physical symptoms and functional impairment. We examined this relationship among Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) military personnel who were first assessed before deployment at a time when we expected to see relatively few physical symptoms and minimal functional impairment, and then assessed again immediately after deployment, 3 months after deployment and one year after deployment. Combat deployment leads to chronic physical symptoms for approximately 30% of Veterans (McAndrew et al., 2016). By examining the cross-lagged relationships between physical symptoms and functional impairment among deploying military personnel, we can better understand these relationships as physical symptoms and functional impairment are developing.