Novel Metrics in the Longitudinal Evaluation of Pain Data in Sickle Cell Disease.

BACKGROUND: Available modalities for the longitudinal capture and analysis of pain intensity in patients with sickle cell disease (SCD) limit our ability to study intraindividual and interindividual variation in pain and the factors influencing the transition from acute to chronic pain in patients with SCD.
OBJECTIVES: The objectives of this study were to determine the feasibility of electronic capture of longitudinal outpatient pain intensity data and to test the applicability of novel metrics in the study of intraindividual and interindividual variation in pain in patients with SCD.
MATERIALS AND METHODS: Twenty SCD patients aged 13 to 21 submitted 2045 diary days of pain intensity data over 229 days using a web-based electronic pain diary or through text message.
RESULTS: Participants reported pain (11-point Numerical Rating Score >0) on 1559 diary days (76.2%) suggesting a significant outpatient pain burden. In addition to mean maximum daily pain (MMDP), using maximum daily pain (MDP) scores, we calculated the ninetieth percentile (p90) of MDP, proportion of pain-free days (PPFD), Standard Deviation (SD) of MDP and coefficient of variation (CV) of MDP. Although p50 of MDP and p90 of MDP correlated positively with MMDP, PPFD correlated negatively with MMDP and both MMDP and PPFD correlated poorly with the SD of MDP. Examination of graphic representation of pain trends demonstrated how patients with similar MMDP had varying p90, PPFD, SD/coefficient of variation, and ultimately burden of pain over time. Missing data rates were lowest in the first 30 days of reporting and increased over time. Study participants reported a positive experience with momentary pain reporting and improved communication with health care providers regarding pain.
CONCLUSIONS: The longitudinal collection of pain data with the inclusion of hospital data during periods of hospitalization is feasible and acceptable in patients with SCD over periods of 30 to 60 days. Long-term collection of pain diary data, while informative, is associated with higher rates of missing data. Novel metrics of pain have the potential to better describe intraindividual and interindividual variation in pain, inform studies of the transition from acute to chronic pain as well as contribute patient-reported end points of pain for interventional clinical trials of pain in SCD.