"Eficacia de la Terapia de activación Conductual Para Pacientes Con Dolor crónico: Ensayo clínico Randomizado"

Chronic pain is a word-wide major health problem, which seriously affects the quality of life of those who experience it and causes important socio-economical costs (Tsang et al., 2008). According to the results of the last Chilean National Health Survey (2010), 34.2% of Chileans older than 15 years present pain ranging from moderate to severe. The pain experienced by a considerable proportion of these individuals (73.5%) is chronic. Among Chileans, chronic pain has been found to be related to more sickness leaves, a five-time increase in the use of primary care services, and the presence of depressive disorders (Miranda et al., 2013). In fact, around 35% patients with chronic pain suffer from depression (Gracely, Ceko, & Bushnell, 2012). In the case of some specific pain disorders such as fibromyalgia, this comorbidity is even greater (life prevalence around 90% for depressive symptomatology and 62-86% for major depressive disorder; Gracely et al., 2012). As a result, some authors posit that fibromyalgia and depression are two manifestations of a single affective spectrum disorder (Gracely et al., 2012). In fact, according to some evidence, both disorders share pathophysiological aspects. For example, pharmacological treatment of both fibromyalgia and depression includes the same dual serotonergic and noradrenergic agonists, namely, amitriptyline and duloxetine (Maletic & Raison, 2009).

Depressive symptoms impair chronic pain treatment and are associated with a worse chronic pain prognosis (Li, 2015). The increasing and concomitant prevalence of depression and chronic pain represents a burden for the primary care systems. Providing effective and appropriate primary care interventions to address this comorbidity is indeed needed, considering that chronic pain and depression lead to great disability. Taking into account that reducing disability is part of the second strategic objective of the Health Goals of the Decade 2011-2020 for Chile, the design and dissemination of therapeutic strategies aimed at the treatment of these problems is a priority in this country.

Behavioral Activation (BA) is an evidence-based psychological intervention for depression (Cuijpers, Van Straten, & Warmerdam, 2007; Dimidjian, Barrera, Martell, Muñoz, & Lewinsohn, 2011). It has been shown to be as effective as comprehensive cognitive behavioral therapy (Cuijpers et al., 2007) and antidepressant therapy (Dimidjian et al., 2006), with a lower dropout rate than the latter (Dimidjian et al., 2006). There is also evidence that BA works as well as medication and better than cognitive behavioral therapy in the treatment of severe depression (Dimidjian et al., 2006). Moreover, several meta-analyses support the efficacy of BA for the treatment of depression (Cuijpers et al., 2007; Ekers, Webster, Van Straten, Cuijpers, Richards, & Gilbody, 2014; Mazzucchelli, Kane, & Rees, 2009). According to the result of the last meta-analysis conducted (Ekers et al., 2014) - in which 26 randomized controlled trials (RCTs) were analyzed with a total of 1,524 participants - the treatment with BA is superior to the control condition (usual treatment, placebo, or waiting list), showing a high effect size (standardized mean difference, SMD: -0.74, 95% CI -0.91 a - 0.56). In addition, the examination of four RCTs with 283 participants showed that CT is also superior to medication. In this case the effect size was moderate (SMD -0.42, IC -0.83 to -0.00). Finally, according to the results of different studies conducted with several populations, BA can be used in multiple contexts and populations (Dimidjian et al., 2011) such as adolescents (Jacob, Keeley, Ritschel, and Craighead, 2013), seniors (Quijano et al., 2007), university students (Gawrysiak, Nicholas, & Hopko, 2009), and primary care patients (Uebelacker, Weisberg, Haggarty, & Miller, 2009).

More research on the efficacy of BA is still needed, especially with regard to its effect after follow-up; however the results reported so far are promising. Furthermore, BA is much easier to apply and disseminate than other psychological treatments. For these reasons, there is now an increasing interest in examining the efficacy of this intervention in populations with different comorbidities such as obesity, cancer, anxiety, borderline personality, substance abuse, childhood abuse history, smoking, and post-traumatic stress disorder, among others (Dimidjian et al., 2011).

BA could be particularly suitable for treating depression among patients with chronic pain, as some of its main purposes are fighting inactivity, increasing environmental reinforces, and decreasing aversive experiences. Indeed, inactivity, loss of reinforces, and excessive unpleasant experiences seem to play a key role in the etiology of both depressive disorders and chronic pain (Dimidjian et al., 2011, Leeuw et al. 2007). According to Lewinsohn's integrative model of depression (Lewinsohn, Hoberman, Teri, & Hautzinger, 1985), when a person with certain vulnerabilities faces a stressful event, that event and the emotions associated with it interrupt their normal behavior patterns, reduce the availability of the reinforcers in the environment, and increase the rate of aversive experiences. All this finally leads to depression. Depressive symptoms have a series of behavioral, cognitive, and emotional correlates that make the subject more vulnerable to new stressful events, thus creating a pathological cycle that is self-perpetuating in time. Something similar occurs when a person suffers a painful injury. According to Vlayen and Linton's Fear and Avoidance Model (FAM, 2000), in the face of a painful injury, vulnerable individuals (with increased pain catastrophizing or increased pain-related fear) develop strategies aimed at avoiding pain and the activities that cause it. This leads to inactivity, loss of reinforcers, disability, and depression, and consequently, to the exacerbation of the pain intensity and pain-related anxiety and catastrophizing. The patient is trapped in a vicious circle of symptoms that feed-back each other and perpetuate over time. Taking into account the FAM assumptions, as well as the purpose of the BA, this treatment may likely not only be useful for reducing depression in patients suffering from pain, but also for reducing the intensity of their pain and the anxiety and catastrophism associated with it. BA could break the chain of perpetuation in both disorders. In fact, there are preliminary data that support this premise. In a case study, in which BA was used with a woman who had been suffering from chronic pain associated with a diagnosis of fibromyalgia for 11 years, a clinically significant decrease in depressive symptoms was observed after treatment. In addition, the degree in which the pain interfered with the patient's daily activities was reduced (in a 100%), as well as pain-related anxiety and the use of pain medication use. These results (with the exception of reduction in medication use) were maintained within three months of the intervention (Lundervold, Talley, & Buermann, 2006). These same authors replicated these findings in another study, in which they applied the same treatment to another woman who had been suffering from fibromyalgia for 22 years. In this case, the decreases of pain intensity, pain-related anxiety, depression, and medication use were maintained three and six months after the intervention (Lundervold, Talley, & Buermann, 2008).