Neuropathic pain in patients with primary knee osteoarthritis: A cross-sectional study

Background: Pain in knee osteoarthritis (OA) may have a neuropathic component. We used the Douleur Neuropathique in 4 questions (DN4) questionnaire to assess neuropathic pain in knee OA and to identify factors associated with neuropathic pain. Methods: A total of 161 patients with knee OA satisfying the American College of Rheumatology 1986 classification criteria for knee OA were prospectively studied. DN4 questionnaire was administered; a score of ≥4/10 was classified as diagnostic for neuropathic pain. The Indian version of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) was used to assess pain, stiffness, and physical function. Factors associated with neuropathic pain were explored. Results: Mean age was 55.7 [+ or -] 8.8 years. The mean total Indian WOMAC was 75.07 [+ or -] 13.8 and WOMAC pain score was 16.1 [+ or -] 3.6. Seventy-nine patients of 161 (49%) had DN4 score ≥4 (neuropathic pain present). When diabetics were excluded (n = 58), the proportion of patients with DN4 score ≥4 reduced to 45.6%. The most frequently described pain characteristic was sensation of electric shock (58.4%). Mean total WOMAC and physical function subscale were significantly higher in neuropathic pain group when compared to the group without neuropathic pain (DN4 ≤3), 77.5 [+ or -] 11.5 versus 72.6 [+ or -] 15.5, P = 0.024 and 54.3 [+ or -] 8.8 and 49.8 [+ or -] 12.6, respectively, P = 0.008. Conclusions: Neuropathic pain (DN4 ≥4) was seen in up to 49% patients with knee OA. Centrally acting drugs such as tricyclic antidepressants or duloxetine can be used to improve the quality of life and physical function of knee OA patients with neuropathic pain.