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Received Apr 18, 2017; Accepted Jul 18, 2017
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1. Introduction
Chronic pain (CP) is a worldwide public health problem that causes a substantial burden on healthcare systems and society, taking into account its high prevalence, economic costs, and the quality of life impairment of the patients and their families. CP requires a multidisciplinary approach for its adequate assessment and management [1–5]. For more than twenty years, the International Association for the Study of Pain (IASP) defined chronic CP as “pain that persists beyond normal tissue healing time, which is assumed to be 3 months” [6]. Variations in the definition of CP between and within countries, differences in standards of living and healthcare resources, high prevalence of pain-generating diseases, cultural background, and local traditions can help explain the estimated CP prevalence ranging from 11% to 55% [2, 7–9]. In a recent epidemiological study, CP prevalence in Portugal was estimated at 37% [10]. CP of moderate to severe intensity has been estimated to occur in 19% of European adults and 40% of them reported inadequate management of their pain [8, 11].
CP is one of the most common reasons why people seek medical care [1]. The economic impact of CP in the USA, in 2008, ranged from $560 to $635 billion USD [12]; in Portugal, it was €4611.69 million (in 2010), corresponding to 2.71% of the Portuguese annual gross domestic...