Subgroup-Specific Approaches for Patients at Risk For or With Chronic Pain
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Reviewing the Concept of Subgroups in Subacute and Chronic Pain and the Potential of Customizing Treatments
Adina C. Rusu, Katja Boersma, and Dennis C. Turk
The conundrum of pain
The tradition in medicine is to make a differential diagnosis of patients on the basis of the presence of a set of signs and symptoms that meet the defining criteria for a specific disease and that are inconsistent with alternative diagnoses that may have some similarities. Once a patient receives a diagnosis a specific treatment or set of treatments will be prescribed preferably to cure the disease or at least to alleviate some if not all of the symptoms. However, not all patients exposed to the same pathogens or traumas meeting criteria for the same disease will present to the healthcare provider in the same way if they seek treatment at all and they may not respond to the same treatment in the same way. For example, only a small percentage exposed to an ankle fracture will develop complex regional pain syndrome, similarly a minority of people exposed to motor vehicle collision develop fibromyalgia but some do. Moreover, although a percentage of people who have amputations will develop phantom limb pain many do not.
In many pain syndromes (e.g. fibromyalgia syndrome (FM), chronic headache, low back pain (LBP), temporomandibular disorders (TMDs)), the definitive identification of causative agents is rare and physical findings are only minimally related to patient-reported symptomatology (e.g. pain severity). Even for pain syndromes with relatively clear-cut causative lesions or processes (e.g. osteoarthritis, postherpetic neuralgia, chronic postsurgical pain), the severity of the insult often bears only a modest relationship to the probability or intensity of pain report. For example, the presence of a severe zoster rash, or a unilateral mastectomy, or a near-complete loss of cartilage in the knee joint may produce no pain at all in one individual and severe chronic pain in another, indicting the presence of substantial individual differences in the processing of information related to noxious stimulation. Even when they receive identical treatments for the same diagnosis, responses are variable. In clinical trials, the emphasis tends to be on mean results with much less attention given to the variability in responses. Why do not all individuals exposed to the same insult demonstrate the same physical and psychological responses to the disease or trauma and how can the variability in response to treatment be explained?