Pain intensity variability and its relationship with quality of life in youths with juvenile idiopathic arthritis.

OBJECTIVE: To describe variability of pain intensity experienced by youths with juvenile idiopathic arthritis (JIA) and examine factors related to within-day patterns of pain and the relationship between magnitude of pain variability and quality of life. METHODS: Pain intensity was self-reported on a visual analog scale (VAS; range 0-100) by 112 youths with JIA ages 8-18 years using electronic diaries 3 times per day for 7 days. Average absolute change in pain (AAC) was computed as a measure of the magnitude of pain variability for each participant. Logistic regression was used to examine the relationship between demographic and disease characteristics and the probability of having high pain variability (AAC ≥10 VAS units). Linear regression was used to examine the relationship between quality of life (assessed by the Pediatric Quality of Life Inventory) and AAC. The generalized estimating equations approach was used to examine the relationship between the time of day and pain intensity. RESULTS: The mean ± SD AAC was 15.6 ± 10.5. The majority of youths (65%) had high AAC (≥10 VAS units). Disease severity predicted high pain variability (ß = 0.02, P = 0.044). Higher AAC predicted lower quality of life (adjusted R(2) = 0.194, ß = -0.59, P = 0.003). Within-day patterns of pain intensity varied by JIA subtype and sex. CONCLUSION: This study characterized the pain intensity variability experienced by youths with JIA. Pain variability throughout the day was common, varied by JIA subtype and sex, and was related to quality of life. These findings have implications for future pain research, patient education, and development of clinical interventions for this population.