Daily sleep quality and mood as predictors of pain in children with juvenile polyarticular arthritis.

Children with juvenile arthritis face the health consequences of ongoing, recurrent pain as well as functional and psychosocial burdens. Daily arthritis-related pain is common, and most importantly, daily pain has been shown to predict activity cutbacks (Schanberg, Anthony, Gil, & Maurin, 2003; Schanberg, Gil, Anthony, Yow, & Rochon, 2005). Thus, it is critical to identify predictors of pain in children with juvenile arthritis in order to guide the development of interventions to promote symptom reduction and improve quality of life. Previous research has detected weak associations between disease-related variables and pain (Malleson et al., 2004), suggesting that other factors are involved. Recently, sleep has been identified as an important aspect of the disease experience in children with chronic pain (Chambers, Corkum, & Rusak, 2008; Valrie et al., 2007a), but little research to date has examined sleep as a predictor of pain in children with arthritis. Sleep has been measured via both objective (e.g., polysomnography) and subjective (e.g., standardized questionnaires) methods and the few published cross-sectional studies suggest that children with arthritis experience significant sleep disturbances (Amos, Curry, Drutz, Frost & Warren, 1997; Zamir, Press, Asher, & Tarasiuk, 1998; Passarelli et al., 2006). For example, Bloom, et al. (2003) found that parents of children with arthritis rated their children as having significantly more sleep anxiety, night awakenings, parasomnia, sleep anxiety, and sleep disordered breathing. Moreover, children’s overall sleep reports were significantly related to pain ratings in this study. In a study using objective sleep measures, Passarelli and colleagues (2006) found significantly higher sleep disturbances, characterized by lower sleep efficiency, higher arousal index, and frequent leg movements in children and adolescents with arthritis than in matched controls. Despite preliminary evidence of sleep problems in children with arthritis, no studies to date have had children track variations in sleep and pain under naturalistic circumstances over several weeks in order to examine sleep as a predictor of juvenile arthritis pain. Prospective research designs are well-suited for studying the associations among symptoms and behaviors that are expected to fluctuate over time, such as pain (Stinson et al., 2008) and sleep (Hanson & Chen, 2010). Although sleep difficulties have been documented in children with arthritis, the etiology of sleep problems in juvenile arthritis remains unclear (Labyak, Bourguignon, & Docherty, 2003). Several potential mechanisms have been hypothesized as causing sleep problems in children. Physiological mechanisms have been proposed related to neural circuitry and neurotransmitters underlying sleep and circadian rhythms (Schwartz & Roth, 2008). Other potential mechanisms relate to emotional (e.g., anxiety) or behavioral problems (e.g., bedtime refusal) interfering with sleep (Chorney, Detweiler, Morriss, & Kuhn, 2008; Meltzer & Mindell, 2006). Previous studies of sleep in children with arthritis suggested pain as the cause of sleep problems (Bloom et al., 2002, Passarelli et al., 2006) and no other disease-specific variables have been examined as predictors of sleep problems. However, conceptual models of sleep and pain suggest a complex, bidirectional relationship (Lewin & Dahl, 1999) and recent research in pediatric pain populations has provided more support for sleep as a predictor of pain than the alternate direction of influence. For example, in Ward et al.’s (2008) polysomnography study of children with arthritis, evening pain did not significantly predict sleep parameters measured during the laboratory sleep assessment. A recent longitudinal study by Lewandowski, et al. (2010) also provides support for studying sleep as a predictor of daily pain. Using a sample of adolescents with chronic pain unrelated to a chronic medical illness and a healthy control group, Lewandowski, et al. (2010) found that sleep variables significantly predicted next-day pain reports, but contrary to study hypotheses, daytime pain did not predict sleep at night. Based on these studies and the research priority of identifying predictors of pain in juvenile arthritis, the current study examined sleep as a predictor of pain. A global rating of sleep quality at night was used as the primary sleep measure in order to determine if the subjective experience of sleep influences reported pain. Another unique feature of the current study was to examine the contribution of psychological factors, namely mood, to the pain-sleep relationship. Previous research has suggested that children with arthritis are at an increased risk for internalizing problems (LeBovidge, Lavigne, Donenberg, & Miller, 2003), and the associations between mood, sleep, and pain have long been recognized (Argoff, 2007; Buysse, Germain, Nofzinger, & Kupfer, 2006) in the general psychiatric and behavioral medicine literature, but remain to be established in children with painful medical illnesses. Few studies have examined how these factors are related in pediatric pain populations and only one study of children with chronic or recurrent pain has examined the role of mood in the daily relationship between pain and sleep (Valrie et al., 2008). In order to identify predictors of daily pain variability, the current study examined daily relationships between sleep, mood, and pain in children and adolescents with polyarticular juvenile arthritis over a two-month period. We hypothesized that poorer sleep quality would predict higher pain ratings the following day. Similarly, we expected children with poorer sleep quality overall to have higher pain, on average. We also hypothesized that the relationship between nightly sleep and next-day pain would be weakened at increasing levels of positive mood, such that positive mood would buffer the effects of poor sleep quality on the previous night.