The present epidemiological research evaluated the prevalence of neuropathic pain characteristics in patients with painful knee osteoarthritis (OA) and the plausibility that such neuropathic features were specific of OA.
Outpatients with chronic pain associated with knee OA who attended orthopedic surgery or rehabilitation clinics were systematically screened for neuropathic pain with the Douleur Neuropathique in 4 questions (DN4) questionnaire. Data from medical files and those obtained during a single structured clinical interview were correlated with the DN4 scores. Information on potential confounders of neuropathic-like qualities of knee pain was collected to evaluate as much as possible only the symptoms attributable to OA.
Of 2,776 patients recruited, 2,167 patients provided valid data from 2,992 knees. The DN4 was scored positively (≥ 4) in 1,125 patients (51.9%) and 1,459 knees (48.8%). When patients with potential confounders were excluded, the respective prevalences were 33.3% and 29.4%. Patients who scored positively in the DN4 had more severe pain, greater structural damage, and more potential confounders of neuropathic pain. Three potential confounders conveyed much of the variability explained by regression analyses. However, latent class analyses revealed that the concourse of other factors is required to explain the neuropathic pain qualities.
A relevant proportion of patients with chronic pain associated with knee OA featured neuropathic pain qualities that were not explained by other conditions. The present research has provided reasonable epidemiological grounds to attempt their definite diagnosis and classification.