Chronic unexplained pain is present in many patients, including those with fibromyalgia, chronic whiplash, chronic low back pain, osteoarthritis, headache and chronic fatigue syndrome. An increasing amount of scientific evidence indicates that central sensitization, defined as an increased sensitivity to a variety of stimuli, accounts for chronic ‘unexplained’ pain in the majority of these patients. Central sensitization is not an epiphenonema: Michele Sterling and Gwen Jull have shown that in patients with whiplash, central sensitization modulates the transition from acute to chronic whiplash, and has predictive ability for rehabilitation outcome in chronic whiplash. Science made us understand the mechanisms behind central sensitization, yet few chronic pain studies have used central sensitization as an outcome or even a treatment goal. Here we introduce you with some basic issues addressing the recognition and treatment of central sensitization in patients with chronic pain.
One of the main characteristics of central sensitization in patients with chronic pain is a generalized rather than a localized decrease in pressure pain threshold. ‘Generalized’ implies more than a segmental spreading of the symptom area, in that it means that the increased sensitivity is localized at sites segmentally unrelated to the primary source of nociception (e.g. the lower limbs in case of a whiplash trauma). In addition, central sensitization entails much more than generalized hypersensitivity to pain and pressure (touch): it is characterized by an increased responsiveness to a variety of stimuli including chemical substances, cold and heat temperature, electrical stimuli, stress, emotions, and mental load. The clinical picture is suggestive of a general intolerance to all kinds of physical and emotional stressors and hence a large decreased load tolerance of the human body in general.
I guess you can now relate the clinical picture to some of your patients. If not, some of the following typical examples might help you out. Some patients spontaneously mention that a hug by their partner can be painful. Others wear sunglasses inside buildings even during the winter time (hypersensitivity to light), while others turn down the radio volume even when it is already low (hypersensitivity to sound). Hyper-responsiveness to mechanical stimuli entails exaggerated responses to active and passive movements as well. Finally, less obvious symptoms may also be related to central sensitization. ‘Central’ symptoms such as fatigue, concentration difficulties, sleep disturbances, and non-refreshing sleep are all frequently experienced by patients with central sensitization. If you want to learn more about to recognize central sensitization in patients with chronic pain, please refer to the following paper: Nijs J, Van Houdenhove B, Oostendorp RAB. Recognition of central sensitization in patients with musculoskeletal pain: Application of pain neurophysiology in manual therapy practice. Manual Therapy 2010;15:135-141.
Once recognized, how can we - physical therapists - account for central sensitization in patients with chronic pain? Or can we treat central sensitization? In despite of some hopeful scientific findings, this remains an unsolved question. Still, we know now that central sensitization is a highly dynamic mechanism, which is good news for our patients. It implies that it can get worse, but recovery is possible as well! The first thing you need to do as physio is explaining the mechanism of central sensitization to your patients. This is not only fun, but it is highly effective for improving pain cognitions, illness perceptions and quality of life in patients with chronic pain. Pain neurophysiology education has been studies in many randomized controlled trials, and each of them turned out very positive. For an overview and clinical practice guidelines, please refer to: Nijs J, van Wilgen CP, Van Oosterwijck J, van Ittersum M, Meeus M. How to explain central sensitization to patients with ‘unexplained’ chronic musculoskeletal pain: Practice guidelines. Manual Ther 2011;16:413-418. In addition, stress management should be an important aspect of the treatment of central sensitization: the hyperexcitability of the somatosensory system in people with chronic pain is likely to be related to the stress response system (i.e. the hypothalamic-pituitary-adrenal axis and the autonomic nervous system).
Finally, graded activity programs, cognitive behavioral therapy and acceptance and commitment therapy are in line with the treatment of ‘cognitive-emotional sensitization’. Physical therapists can really improve their skills and ability to help chronic pain patients by adopting (parts of) such established treatments in their daily practice. Moreover, by combining such treatments with pain neurophysiology education, one can incorporate such ‘psychological’ treatments into the neuroscience model of central sensitization, which makes it more accessible and acceptable to many patients (even those reluctant to psychological approaches). An overview of all treatment options, including drugs and medical treatment, can be found in the following paper: Nijs J, Meeus M, Van Oosterwijck J, Roussel N, De Kooning M, Ickmans K, Matic M. Treatment of central sensitization in patients with ‘unexplained’ chronic pain: what options do we have? Expert Opinion on Pharmacotherapy 2011; 12(7):1087-98.