Offset Analgesia as a Measure of Central Sensitization in Children

Specific Aims/Objectives To date, OA has not been evaluated in pediatric chronic pain disorders. In the current study, the investigators plan to measure OA responses in a population of common pediatric pain disorders. The primary objective of this study is to determine if OA paradigm can detect impairment of central inhibitory modulation pathways in subgroups of chronic pain disorders in children and adolescents. The investigators hypothesize that chronic pain in children and adolescents results from central sensitization and impaired central inhibitory modulation of pain and thus children with chronic pain disorders will have a decreased OA response compared with healthy controls. If the results of this study are positive, this testing paradigm could be a valuable objective marker in examining the efficacy of pharmacological and/or rehabilitative treatment modalities in reversing or alleviating central sensitization-induced pain in children with chronic pain disorders. Additionally, if existing self-report questionnaires, Pain Sensitivity Questionnaire (PSQ) and Central Sensitivity Inventory, correlate with the magnitude of offset analgesia observed, they could be used to screen for central sensitization in high volume and busy clinical settings. Aim 1: To determine if children with common chronic pain disorders, including musculoskeletal pain, complex regional pain syndrome, functional abdominal pain and chronic headaches demonstrate impaired ability to actuate central descending inhibitory function as measured by a test of offset analgesia. To accomplish this aim, the investigators will compare 30 children with common chronic pain disorders with 30 age and sex matched controls. Power will be 80% to detect a 20% or larger difference in the change in self-reported pain scores as a result of the dynamic heat pain test stimulus between the two groups using a Student t-test (nQuery Advisor version 7.0, Statistical Solutions, Cork, Ireland). Aim 2: To determine if the Pain Sensitivity Questionnaire (PSQ) and/or Central Sensitization Inventory (CSI) can serve as screening tools for assessment of central sensitization i.e., impairment of central descending inhibitory function in children with common chronic pain disorders. To accomplish this aim investigators will correlate scores on the above scales with the magnitude of offset analgesia using Pearson correlations in 30 children with chronic pain disorders and 30 healthy age and sex-matched controls. The investigators hypothesize that the magnitude of OA will correlate with either PSQ, CSI or both thus these questionnaires would serve as assessment tools for central sensitization in children with common chronic pain disorders in clinical setting. The Mann-Whitney U-test will be applied to compare medians and interquartile ranges on the PSQ and CSI between the chronic pain and healthy control groups. In addition, investigators will identify individuals who show a decrease in VAS pain scores after the dynamic test stimulus of at least 20% (responders) and will assess whether PSQ and CSI can predict responders and non-responders using a receiver operating characteristic (ROC) curve approach with area under the curve (AUC) to measure how well pain perception and central sensitization assessment tools can help to identify responders and non-responders.