The International Association for the Study of Pain (IASP) is considering a new descriptor for the mechanism of chronic pain to help treat the large number of patients whose condition cannot be described as either nociceptive or neuropathic.
Creating a new descriptor of chronic pain may provide clearer prescribing options for GPs -- drug therapies where appropriate and non-drug therapies such as referral to allied health professionals for patients with chronic pain which is neither nociceptive nor neuropathic.
Professor Milton Cohen, director of the St Vincent’s Hospital Pain Clinic in Sydney, and international colleagues are arguing that the 2011 redefinition of neuropathic pain excludes a large group of patients who do not have obvious neuropathy, defined as disease or damage to the somatosensory system.
“GPs need to recognise that neuropathic pain has quite a narrow definition – it’s not just the default descriptor for pain that isn’t nociceptive. It’s pain that is due to neural disease or damage,” Professor Cohen says.
“However this doesn’t cater for a whole lot of people who have pain that is not nociceptive but have features suggestive of neuropathic pain such as sensitivity to touch, easy exacerbation and spread, yet they don’t have neuropathy. We need a third descriptor.”
Professor Cohen says this group of patients typically have diagnoses including fibromyalgia, complex regional pain syndrome (CRPS) type 1, musculoskeletal pain (such as non-specific chronic low back pain), and functional visceral pain disorders (such as irritable bowel syndrome and bladder pain syndrome).
This pain has previously been referred to as unknown or idiopathic, but these terms do not describe the mechanism. The pain likely involves a change in nociceptive processing, probably in the central nervous system, Professor Cohen says.
“One of the problems is that the descriptor neuropathic pain has been taken as a catch-all diagnosis which has kept the focus on drug treatment, but these days we recognise that drug treatment is only an adjunct.
“GPs shouldn’t keep searching for a broken part. A thorough physical examination will indicate whether there is a waiting-to-be-diagnosed problem, but we have to recognise the role of the central nervous system in chronic pain and pay much more attention to the context in which this is occurring.”
The IASP is considering a number of options for the new descriptor. The next step will be to define a set of clinically useful positive classification criteria, Professor Cohen says.
These clinical descriptors are complementary to new classifications of chronic pain to be introduced in the upcoming 11th revision of the World Health Organisation’s International Classification of Diseases (ICD), due to be voted by the World Health Assembly in 2017.
ICD-11 is considering the introduction of the term Chronic Primary Pain in cases that cannot be better explained by another chronic pain condition.
Clinical descriptors (according to 2011 IASP redefinition)1
Nociceptive pain: Pain that arises from actual or threatened damage to non-neural tissue and is due to activation of nociceptors.
Neuropathic pain: Requires a demonstrable lesion or a disease that satisfies established neurological diagnostic criteria.
New descriptor: Is intended to apply to pain states characterised by clinical and psychophysical findings that suggest altered nociception, despite there being no clear evidence of actual or threatened tissue damage or evidence for disease or lesion of the somatosensory system
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