Pain, Emotional Allodynia, and Relational Load (PEARL): Protocol of a Multicenter Observational Case-Control Study...

Background: The International Association for the Study of Pain defines pain as a sensory and an emotional experience, yet no instrument in routine practice quantifies affective hypersensitivity to low-intensity interpersonal stimuli, a pattern we term emotional allodynia, a construct transposed from thermal stimuli in major depression, which this study sets out to validate rather than assume. The Emotional Allodynia Questionnaire (AEQ), an 11-item self-report measure, was preliminarily validated in a single-center fibromyalgia sample, showing excellent internal consistency and a unidimensional structure. This protocol describes the multicenter validation phase. Methods: PEARL is a prospective, multicenter, observational case-control study at five Italian tertiary pain centers. Cases are adults with fibromyalgia diagnosed by the 2016 American College of Rheumatology (ACR) criteria; controls are adults with chronic non-cancer pain of defined nociceptive or neuropathic origin. All participants complete the AEQ together with the Central Sensitization Inventory (CSI), Pain Catastrophizing Scale, Beck Depression Inventory-II, State-Trait Anxiety Inventory, Difficulties in Emotion Regulation Scale and a pain visual analog scale, and are reassessed once at 40 ± 10 days. The targets are 274 cases and 151 evaluable controls, sized respectively for the precision of internal consistency within depression strata and for a 95% confidence interval of width 0.10 around an area under the curve of 0.80. Analyses cover internal structure, convergent and discriminant validity, test-retest reliability, AEQ-CSI phenotyping and covariate-adjusted discrimination. Results: Results are not yet available; recruitment began on 10 September 2025 and should be complete by approximately December 2027. Conclusions: The preliminary phase could not say whether the AEQ separates fibromyalgia from other chronic pain, whether the construct holds over time, or whether it survives adjustment for depression, anxiety, catastrophizing and emotion dysregulation. PEARL is designed to test these three questions, and to examine whether the AEQ-CSI phenotypes replicate. Registered on ClinicalTrials.gov (NCT07677631).