medwireNews: Enough patients with knee osteoarthritis (OA) experience pain with neuropathic characteristics to warrant attempts to diagnose and classify these features, say researchers.
They found that among 2176 patients with OA, a third scored positively for neuropathic pain on the Douler Neuropathique in 4 questions (DN4) questionnaire, after patients with reasons other than OA for such pain had been excluded.
Analysis showed that three of these potential confounders – conditions other than OA that cause changes in cutaneous sensory perceptions on the knee, or cause abnormal sensations over the area of the knee, and referred back or hip pain – were highly specific for neuropathic pain, but less sensitive than the DN4.
“[W]hen these factors are absent, the presence of neuropathic pain is unlikely, yet the DN4 can sense additional neuropathic features in some patients,” explain the researchers, led by Ángel Oteo-Álvaro (Hospital General Universitario Gregorio Marañón, Madrid, Spain).
Further confirmation and classification of these additional features could reveal links between neuropathophysiology and signs and symptoms of the condition, they note.
“For example, the selective blockade of Aβ-fibers supplying the knee could provide useful information about putative neuropathic mechanisms contributing to knee OA pain or to develop new therapies for it”, the researchers write.
Of the 2176 participants, 1125 (51.9%) had a positive DN4 score of at least 4 points. This fell to 33.3% after patients with confounders had been excluded.
Those patients who scored positively on the DN4 had more severe pain, greater structural damage and more potential confounders of neuropathic pain.
Oteo-Álvaro and colleagues say that their findings are supported by animal models, examples of which include the demonstration of peripheral lesions, markers of nerve injury and regeneration, the involvement of microglia and changes in the functional properties of primary afferent Aβ-fibres among others.
Small interventional studies have also shown clinical benefit in knee OA patients taking analgesic treatments targeting neuropathic pain over and above that seen with analgesic drugs prescribed for nociceptive pain, the researchers add in Pain Practice.
“[W]e have shown that the presence of neuropathic mechanisms contributing to the pain associated with knee OA is plausible”, they conclude.