Chronic pain not only causes physical pain, but also induces severe emotional, functional, social and spiritual stresses. Treatment of chronic pain (pharmacological, surgical, psychological) provides only partial relief for most patients, with the efficacy of existing medications often blunted by dose-limiting side effects.
According to definition of 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". Chronic pain (pain lasting more than 3 months) has gradually emerged as a distinct phenomenon in comparison with acute pain. In chronic pain, the pain is no longer serving as a warning signal but becomes a disease per se.
According to the French “Haute Autorité de Santé” (HAS), chronic pain, regardless of topography and intensity, is defined when the pain has several of the following characteristics :
- persistence or recurrence beyond what is usual for the initial presumed cause, particularly if the pain has been present for more than 3 months
- insufficient response to treatment
- significant and progressive deterioration in the patient's everyday functional and relationship capacity related to the pain, at home, in education or at work.
When chronic pain becomes "refractory"
The refractory character of chronic pain is included in the definition, which considers the chronic pain as a pain with insufficient response to treatment. However, the HAS doesn’t use explicitly the term ‘refractory’ (‘rebelle’ in French) considering that this term is ambiguous because it has many meanings and may encompass other terms as “intractable”, “resistant to treatment”, “difficult to analyze”, “fluctuant pain” or “pain associated with a rebellious comportment of patient”.
Due to the lack of clear definition of the “refractory” character of pain, epidemiological data about prevalence and burden of refractory chronic pain (rCP) are lacking too. The burden of chronic pain is however major. In the Global Burden of Disease Study, 5 chronic pain states appear in the top 20 causes of global years lived with disability (YLDs), accounting forabout 159 millions YLDs in the world: low back pain (1st rank), neck pain (4th), migraine (6th), osteoarthritis (13th) and medication overuse headache (18th rank). Such societal burden is partially explained by the high prevalence of chronic pain, estimated to 31.7%, in France, including 6.9% for chronic neuropathic pain (4) and 2.98% for chronic daily headache, and the frequent resistance of these patients to classical analgesic treatments.
Pharmacological, surgical, psychological and alternative medicine approaches for the treatment of chronic pain provide only partial relief for most patients, with the efficacy of existing medications often blunted by dose-limiting side effects. The development of more efficient treatments for chronic pain states has been hampered by the lack of predictive animal models and biomarkers, variation of pain characteristics among patients or an a day-to-day basis for single patients, patient stratification based on the symptoms rather than mechanism and a high rate of placebo responses.
Consequently, very few therapeutic advances in the domain of analgesic drugs have been made in the last years. Translational pain research faces numerous challenges: bridging the gap between pain research and clinical pain management ; developing objective pain-assessment tools; analyzing current theories of pain mechanisms and their relevance to clinical pain; exploring new tools for preclinical and clinical pain research; coordinating efforts among basic scientists, clinical investigators and pain-medicine practitioners.
In light of its fast-evolving nature and its contribution to many other areas of medicine, medical technology has the capacity to help solving these challenges, by developing new objective measures that capture the subjectivity of pain experience or go beyond it and by providing technology-based treatments, and may become an integral part of the diagnosis and treatment of pain.
Considering the burden of pain and the complexity of its management, the French Ministry of Health set up in 1998 a “national pain program” involving tertiary teams to assess and manage refractory chronic pain, leading to the identification of about 250 French pain clinics, regionally organized. In our region, “PACA” (4,8 million residents), there are 13 secondary centers (“pain consultations”) and 2 tertiary “pain centers” (in the 2 main cities Nice and Marseilles) which have a mission of expertise to assess and manage the most difficult chronic pain patients.
In the pain center of the Nice University Hospital (CHU de Nice), the annual number of consultations is about 10 000 with an active list of 3500 patients including 1500 new patients per year. As in other French pain clinics, patients suffering from chronic daily headache, neuropathic pain and low back +/- radicular pain account for about 60% of the recruitment. A significant proportion of these patients are difficult to treat and resist to current multimodal protocols associating classical analgesic drugs and non-pharmacological therapy supported by the biopsychosocial model of chronic pain.
During the last 10 years, the neurosurgical department and pain center of the CHU de Nice have developed close collaborations with the aim to improve the management of these rCP patients. Involving care, research and teaching activities, this collaboration has been particularly focused on surgical neuromodulation to treat refractory neuropathic pain and refractory chronic daily headache (rCDH).