HPE Chronic pain – part one - Page 3

INTRODUCTION Chronic pain: a symptom or a disease? This short overview addresses key concepts to align the definitions and concepts of chronic pain Bart Morlion MD PhD The Leuven Center for Algology, University Hospitals, Leuven, KU Leuven, Belgium Pain is one of the most common reasons for a patient to consult a healthcare professional. One in five adults in Europe is estimated to be affected by chronic pain. 1 What is pain? A frequently used definition of pain was proposed by the International Association for the Study of Pain (IASP): “Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage”. 2 Our nociceptive system is one the fastest and most sensitive defense mechanisms in our body. Mostly, acute pain can be considered as a symptom of an underlying activation of our warning system by internal and/or external harmful stimuli. Recently, the definition of pain has been challenged by alternative proposals. The IASP Definition of Pain Taskforce suggests to define pain as “An aversive sensory and emotional experience typically caused by, or resembling that caused by, actual or potential tissue injury”. 3 Another proposal from 2016 suggests: “Pain is a distressing experience associated with actual or potential tissue damage, with sensory, emotional, cognitive and social components.” 4 Importantly, all these definitions imply the subjective nature of pain experiences. What are pain descriptors? Aside from the distinction between acute and chronic pain, pain syndromes can be divided into three classes according to their clinical features and aetiology. Class 1: Nociceptive pain Nociceptive pain, is physiological protective pain involving activation of high-threshold nociceptor neurons by noxious mechanical, chemical or thermal stimuli (for example, ligamentous stretch or pinprick). Class 2: Inflammatory pain Inflammatory pain is pain hypersensitivity involving detection of active peripheral tissue inflammation by nociceptors and sensitisation of the nociceptive system (for example, facet pain or spondylodiscitis). Class 3: Pathological pain The third class, pathological pain, is not a symptom but, rather, represents a disease state of the nervous system. Pathological pain is not adaptive and has no protective function, and can be divided into two types: nociplastic and neuropathic. Nociplastic pain is the result of nociceptive signaling amplification in the absence of neural lesions or inflammation (for example, fibromyalgia or chronic widespread pain). 5 Conversely, neuropathic pain is a maladaptive plasticity that may or may not be due to a lesion or disease, and affects the somatosensory system and alters nociceptive signal processing so that responses to noxious and innocuous stimuli are enhanced and pain is felt in the absence of stimuli (for example, radicular pain). What is chronic pain? A classification according to duration, speed and time will categorise pain either as acute or chronic. Acute and chronic pain are totally different types of pain. Chronic pain is not just an extension of acute pain. Yet, the duration of the pain is the first criterion to distinguish acute and chronic pain. For many years, chronic pain was defined as “pain without apparent biological value that has persisted beyond the normal tissue healing time (usually about three months)”. 6,7 Recently, the International Classification of Diseases defined chronic pain as pain that lasts or recurs for longer than three months. 8 Although chronic pain may be a symptom of an underlying chronic condition, it frequently outlasts the normal healing process and often no other underlying disease can be identified. The common understanding is that, unlike acute pain, chronic pain has no protective function. Over the last decades, the paradigm of chronic pain shifted from a pure biomedical to a biopsychosocial phenomenon. Indeed, the biopsychosocial model of chronic pain recognises chronic pain as a combination of physical dysfunction, beliefs, coping strategies, distress, illness behaviour and social interactions. Since the introduction of the biopsychosocial model, treatment of chronic pain has become multimodal and multidisciplinary, with the aim of maximising pain reduction, quality of life, independence and mobility. What is pain chronification? The transition from acute to chronic pain is a very complex process involving a plethora of neurobiological and psycho-neurophysiological processes. The development and maintenance of many chronic pain syndromes appears to arise from an imbalance between amplified ascending signals and inadequate activation of the descending inhibitory pathways. A common process is central sensitisation which is defined as “increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input”. 9 hospitalpharmacyeurope.com | 2019 | 3