Effect of neuropathic pain on functional capacity, emotional state, sleep quality and quality of life in patients with knee osteoarthritis

Introduction: Osteoarthritis (OA) is a chronic disease characterized by progressive cartilage destruction, joint pain, limitation of movement and loss of function. OA is one of the leading health problems in the aging population and causes morbidity that severely restricts both social performance and daily living activities of individuals. The most common symptom of OA is pain. The etiology and pathophysiology of pain in OA is not completely clear. However, nociceptive components may not completely explain the symptoms such as hypersensitivity,referred pain and numbness. The aims of our study were to evaluate the existence of neuropathic pain (NP) component and to assess the effect of NP on functional capacity, emotional status, quality of sleep and quality of life in patients with knee OA. Material and methods: Patients who applied to physical therapy outpatient clinics between September 2019 and July 2020, had knee pain for at least 3 months, aged 40-70, and knee OA diagnosis, according to "American College of Rheumatology" (ACR) diagnostic criteria were included in the study. Patients with diseases known to cause neuropathic pain were excluded from the study. Data including age, sex, educational status, working status, comorbidities, body mass index, symptom duration, presence and duration of morning stiffness, were obtained from patients. The presence of crepitation, knee range of motion (ROM) were evaluated on physical examination. The standing antero-posterior radiographs of the patients were evaluated using the Kellgren-Lawrence grading system. The rest, activity, and night pain of the patients were questioned using a 10-point likert scale (VASrest, VASactivity, VASnight, respectively). NP level in all patients was evaluated with the Douleur Neuropathique 4 Questions (DN4) and PainDETECT (PD-Q) scales. Western Ontario and Mc Masters Universities Osteoarthritis Index (WOMAC) and Lequesne Knee OA Severity Index (Lequesne) were used for functional status assessment. Beck Depression Inventory (BDI) and the Beck Anxiety Inventory (BAI) were preferred for the evaluation of the emotional states of the patients, the sleep quality of the patients was evaluated with the Pittsburg Sleep Quality Index (PSQI). Short Form-36 (SF-36) was preferred in the evaluation of quality of life. Our study was performed on 100 patients with knee OA. Results: The mean age of the patients was 58.8 ± 7.2 years (between the ages of 46-70). 79% of the patients were women and 21% were men. NP accompanied 46% of the patients (n=46) according to the DN4 scale (DN4≥4) and 20% (n=20) of the patients according to the PD-Q scale (PD-Q≥19). 37% of the patients (n=37) had depression when evaluated with BDI, and 46% (n=46) had anxiety disorder when evaluated with BAI. Sleep quality was poor in 47% of the patients (n=47) according to the PSQI score. Age, sex, education level, professional status and BMI of patients with NP were similar to those without NP (p≥0.05). In patients with DN4≥4, symptom duration, frequency and duration of morning stiffness, Kellgren-Lawrence grade, all VAS values, PD-Q, WOMAC, Lequesne, BAI, PSQI scores were higher than those with DN4<4 (p<0.05 for all analyses), but physical functioning, social functioning and pain subscores of SF-36, right knee ROM were lower. In patients with PD-Q≥19, symptom duration, duration of morning stiffness, waist circumference, all VAS values, DN4, WOMAC, Lequesne, BDI, BAI, PSQI scores were higher than those with PD-Q<19 (p<0.05 for all analyses), but physical functioning, social functioning and pain subscores of SF-36, right knee ROM were lower. Conclusion: Although pain in knee OA is generally considered as nociceptive, a significant portion of patients have neuropathic component. NP component is associated with higher levels of nociceptive pain, severity of knee OA, reduced functionality, impairment in quality of sleep, quality of life, depression and anxiety levels. Key words: Knee Osteoarthritis, Neuropathic pain, Quality of life, Functional status, Sleep quality, Mood