Neuropathic pain: An updated grading system for clinical and research settings
Pain usually occurs from activation of nociceptive afferents by actual or potential tissue-damaging stimuli. Pain may also results by activity generated within the nervous system without adequate stimulation of its peripheral sensory endings. For such type of pain, the International Association for the Study of Pain Special Interest Group (SIG), redefined the neuropathic pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system," in 2008.
The authors also attempted to revise a new grading system to palliate the absence of diagnostic tools for neuropathic pain. This grading system is aimed for clinical and research purposes to determinine the confidence level for pain of neuropathic origin and classified into 3 levels of certainty: definite, probable and possible. However, the grades probable and possible require confirmatory evidence from a neurologic examination.
The grading system of possible, probable and definite neuropathic pain has been used since 2008, but did not gather support. Special Interest Group (SIG) held a committee with expert panel and recommendations for an improved grading system, its pros and cons with a mandate to propose improvements.
The authors had performed a systematic review for articles citing the 2008 paper with the help of Scopus and concentrated on citation use, publication classification criteria for neuropathic pain classification, issues raised, and inclusion of other criteria for neuropathic pain diagnostic. Out of 731, total 608 articles were identified in the Scopus database and used to examine the use of grading system, 414 of which cited the neuropathic pain definition. Of 220 clinical studies citing the paper, 56 used the grading system and 16 used alternate classification criteria. The remaining 115 used an alternate set of criteria for neuropathic pain classification: 50/115 used other questionnaires including Douleur Neuropathique en 4 questions (30 [in French]), painDETECT (11), Leeds Assessment of Neuropathic Symptoms and Signs (LANSS, 8).
Futher, with the aid of these questionnaires, limitations were identified and 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). Paramount advancements made in the grading system included; a revised order of grading criteria, a closer reflection of clinical practice, an improved language clarity and prefered inclusion of questionnaires. In future studies, gaps (absence of positive criteria for a non-neuropathic pain diagnosis, and difficulty in assessing sensory function in deep tissues) pointed out by the authors should be addressed for understanding of neuropathic pain.
With these implications, authors anticipate that this improved grading system will spread its use among (non-) neurologists, these efforts allowing clinicians to better accommodate treatment in case of uncertain neuropathic pain diagnosis.