The International Association for the Study of Pain Special Interest Group (SIG) for the Study on Neuropathic Pain modified the definition of neuropathic pain in 2008 as “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system.” 1 Authors also proposed a new grading system to palliate the absence of diagnostic tools for neuropathic pain, aimed at determining the level of confidence for pain of neuropathic origin in both clinical and research settings. This grading system classifies neuropathic pain in 3 levels of certainty: definite, probable and possible, the latter 2 requiring supporting neurologic findings.
As this grading system has not gathered widespread support, the SIG established a committee, gathering pain specialists from around the world with the mission of evaluating the 2008 grading system, and in particular, its usefulness and limitations, in order to propose improvements. Key findings and conclusions were recently published in Pain.2
Authors performed a systematic database search for articles citing the 2008 paper, using Scopus, and focusing on citation use, publication classification (i.e. review, research article, clinical study, or other), criteria for neuropathic pain classification, issues raised, and inclusion of other criteria for neuropathic pain diagnostic.
Committee members were provided with results from this literature review ahead of a meeting which took place in May 2015, and during which they were asked to provide feedback on the grading system; discussions which took place at the meeting were used in addition to feedback from committee members to formulate an improved grading system.
Out of the 731 publications identified in the Scopus database and citing the 2008 report, 608 were used to examine use of the grading system. Among these, 269 were review articles, 220, clinical studies, 73 were research articles, and 46 were classified as ‘others’. 414 of the 608 publications cited the paper in relation with the definition of neuropathic pain; 92 publications used alternate definitions of neuropathic pain.
Among the 220 clinical studies citing the 2008 report, 56 used the ‘possible/probable/definite‘ grading system for neuropathic pain, 16 used alternate classification criteria, but also made use of the grading system. The remaining 115 used an alternate set of criteria for neuropathic pain classification: 50/115 used other questionnaire(s), including Douleur Neuropathique en 4 questions (30 [in French]), painDETECT (11), Leeds Assessment of Neuropathic Symptoms and Signs (LANSS, 8).
Limitations identified by committee members included: questionnaires established prior to redefinition of neuropathic pain, difficulty determining lesion location and pathology, presence of atypical sensory signs for neuropathic pain, and lack of causality between lesion and pain. These identified limitations were used to revise the grading system, designed to be used in conjunction with patient history, clinical examination and tests.
In the revised grading system, neuropathic pain is assessed as being possible in patients presenting with a history of neurological lesions or disease and a distribution of pain consistent with a disease of the somatosensory nervous system or the location of detected lesion(s). A probable categorization of neuropathic pain requires negative sensory symptoms, also consistent with disease or lesion. Finally, definite neuropathic pain categorization requires lesion/disease confirmation using diagnostic tests (e.g. CT, MRI, skin biopsy, nerve conduction velocity test).
Major improvements to the grading system were a revised order of grading criteria, a closer reflection of clinical practice, an improved language clarity and better inclusion of questionnaires. Authors pointed to gaps in our understanding of neuropathic pain, which they thought should be addressed in future studies. These included the absence of positive criteria for a non-neuropathic pain diagnosis, and difficulty in assessing sensory function in deep tissues, often the siege of neuropathic pain.
Authors hope that this improved grading system will extend its use among (non-) neurologists, allowing clinicians to better adapt treatment in case of uncertain neuropathic pain diagnosis.
1.Ochoa JL. Neuropathic pain: redefinition and a grading system for clinical and research purposes. Neurology. 2009;72(14):1282-3.
2.Finnerup NB, Haroutounian S, Kamerman P, et al. Neuropathic pain: an updated grading system for research and clinical practice. Pain. 2016.