HPE Chronic pain – part one | Page 6

OVERVIEW Chronic low back pain: an overview This article provides an overview of the epidemiology of low back pain, its aetiology, and differential diagnosis. Current treatment recommendations are reviewed as well as new therapeutic approaches under development Rainer Freynhagen MD DEAA Professor, Chair, Department of Anaesthesiology, Critical Care Medicine, Pain Medicine & Palliative Care, Pain Center Tutzing Feldafing, Benedictus Hospital Feldafing; Academic Teaching Hospital Technische Universität München, Feldafing, Germany According to the World Health Organization, low back pain is highly prevalent in Western countries and one of the major contributors to loss of quality of life as well as absenteeism. The condition can be classified, according to the duration of pain, as acute (less than 6 weeks), subacute (lasting from 6 to 12 weeks), and chronic (more than 12 weeks). Although occupation and working conditions, obesity, lifestyle, body height, and age are some of the known risk factors, the exact causes of low back pain still need to be fully elucidated and its diagnosis is not always straightforward. It is clear, however, that the chronic form of the disease, which is frequently associated with comorbidities such as depression, panic/anxiety disorders, and sleep disturbances and may even lead to long-term disability, poses a substantial burden to societies and health care systems alike. 1,2 Epidemiology and pathophysiology In 2010, the World Health Organization ranked low back pain already among the top ten diseases and injuries worldwide in terms of highest number of disability-adjusted life years. Its lifetime prevalence is estimated to be between 60% and 70% in industrialised countries, with an incidence of 5% per year among adults. The incidence of low back pain reaches its peak at ages 35–55 years, and its overall prevalence increases until 60–65 years and then slowly decreases. 1 A recent systematic review of the literature describing studies reporting prevalence data from medical records in the US, Canada, Sweden, Belgium, Finland, Israel, and the Netherlands revealed a wide range of values, from 1.4% to 20%. 3 A total of 37% of the cases worldwide can be attributed to working postures and repetitive movements. 1 The Global Burden of Disease Study, conducted in 2015, reported a global point prevalence of activity-limiting low back pain of 7.3%, corresponding to 540 million people, and low back pain is now regarded as the first cause of disability worldwide. 4 About 90% of all patients will have non-specific low back pain, which, in essence, is a diagnosis based on exclusion of a specific pathology. Non-specific low back pain has an estimated point prevalence of 18%. 5 Many physiological mechanisms may act to cause low back pain. Therefore, the traditional binary classification of pure nociceptive (arising from damage to non-neuronal tissue and activation of nociceptors) pain or neuropathic pain (due to a lesion/disease affecting the somatosensory system) was limited in the sense that it was inaccurate and did not cover all patients. For this reason, the term 6 | 2019 | hospitalpharmacyeurope.com ‘mixed pain’ was adopted to designate low back pain with overlapping nociceptive and neuropathic symptoms. Therefore a first definition has been published recently: Mixed pain is a complex overlap of the different known pain types (nociceptive, neuropathic, nociplastic) in any combination, acting simultaneously and/or concurrently to cause pain in the same body area. Either mechanism may be more clinically predominant at any point of time. Mixed pain can be acute or chronic. 6 Why is that so important? A systematic review of chronic low back pain studies highlighted that 20–55% of patients had a greater than 90% likelihood of having a neuropathic pain component, and a meta-analysis of 20 studies describing the prevalence of the neuropathic component showed values ranging from 25% to 73%. 7,8 What is known is that it has a substantial economic impact and can lead to suboptimal treatment. The costs of treatment for patients with back pain plus a neuropathic component can, in fact, be 50% higher than the costs incurred by the average patient. 2 A model of prevalence and cost for back pain in the general population estimated as much as 67% higher costs for patients with neuropathic back pain compared to those with nociceptive back pain only, and 16% of the total back pain-related costs were attributable to pain with a neuropathic component. 9 A typical neuropathic pain component is radicular low back pain, which radiates below the knee along a dermatome, due to irritation/ inflammation/compression of a lumbar nerve root. Sciatica, a common symptom in different medical conditions, can be caused by nerve compression owing to a protruding intervertebral disk or inflammation. Pseudoradicular pain, however, mimics irritation of the nerve root and, while it projects to the extremities, it cannot be attributed to a typical dermatome of a nerve root. This distinction is relevant from the clinical point of view because projected pain has necessarily a neuropathic component, whereas referred pain may be predominantly nociceptive. Moreover, the therapeutic strategies followed for these two conditions are theoretically distinct, with nociceptive pain being sensitive to drugs as non- steroidal anti-inflammatories (NSAIDs) or opioids and neuropathic pain being more responsive to antidepressants and anticonvulsants. 7 For most patients with low back pain, a self- limited course constitutes the natural history of the disease. Serious causes of low back pain, on the other hand, are uncommon, and an exhaustive search of the aetiology is rarely fruitful.