The Emotional Allodynia Questionnaire (AEQ) is an 11-item self-report instrument that measures disproportionate emotional reactivity to low-intensity interpersonal cues(perceived unresponsiveness, exclusion, loss of reciprocity), a pattern termed emotional allodynia. It was preliminarily validated in a single-center fibromyalgia sample. PEARL (validation phase) is a multicenter, prospective, observational psychometric validation study that (1) replicates the internal structure and convergent validity of the AEQ in an independent fibromyalgia sample, (2) tests its known-groups (discriminative) accuracy in separating fibromyalgia from non-fibromyalgia chronic pain of defined nociceptive or neuropathic origin, expressed as the area under the ROC curve (AUC), and (3) assesses test-retest reliability. There is no intervention.

Design: multicenter (Italian tertiary pain centers), observational, case-control psychometric validation study. Cases are adults with fibromyalgia (2016 ACR criteria); controls are adults with chronic non-cancer pain of defined nociceptive or neuropathic origin who do not meet fibromyalgia criteria. Group membership reflects clinical diagnosis and is not assigned by the investigators.

Assessment: the primary assessment is cross-sectional at baseline (T0). All enrolled participants (cases and controls) are reassessed once for test-retest reliability (T1) at approximately 40 days (plus or minus 10 days). The battery comprises the AEQ, Central Sensitization Inventory (CSI), Pain Catastrophizing Scale (PCS), Beck Depression Inventory-II (BDI-II), State-Trait Anxiety Inventory (STAI-Y forms 1 and 2), Difficulties in Emotion Regulation Scale (DERS), and a Visual Analog Scale (VAS) for pain. Questionnaires are self-administered on paper with physician-verified completeness at the point of care, then transcribed into a secure online data-collection form.

Sample size: two targets. The fibromyalgia cohort comprises 274 patients (137 per depression stratum, sized for internal consistency and depression-stratified estimation; PASS 2024 v24.0.5). For the known-groups discriminative analysis, 151 evaluable non-fibromyalgia chronic pain controls are required, sized on precision for a 95% confidence interval of width 0.10 around an anticipated AUC of 0.80 (Hanley-McNeil standard-error method, PASS 2024 v24.0.9); the 97-per-group level is the minimum to test an AUC of 0.80 against a null of 0.70 (two-sided alpha 0.05, 80% power; Hanley-McNeil / Obuchowski-McClish).

Primary analysis: ROC analysis with the AEQ total score as classifier and diagnostic group as the reference (fibromyalgia = positive); the AUC is tested against 0.70 with its 95% CI. A covariate-adjusted logistic-regression sensitivity analysis (age, sex, depressive comorbidity) and a center-adjusted analysis are pre-specified. Secondary analyses include convergent and discriminant validity, exploratory and confirmatory factor analysis, test-retest ICC, AEQ-CSI median-split phenotyping (Resilient, Emotional Allodynia, Central Sensitization, Mixed), a pre-specified depression-stratified analysis, and exploratory unsupervised clustering.

CASES (fibromyalgia)

Inclusion Criteria:

• Age 18 years or older
• Clinical diagnosis of fibromyalgia confirmed according to the 2016 revision of the ACR criteria
• Chronic non-cancer pain for at least 3 months
• Ability to understand and independently complete self-report questionnaires in Italian
• Willingness to provide written informed consent

Exclusion Criteria:

• Active oncological disease or cancer-related pain
• Any current or past psychiatric diagnosis except Major Depressive Disorder and Panic Disorder (assessed by clinical history)
• Severe cognitive impairment precluding questionnaire completion
• Inability to understand or complete questionnaires in Italian

CONTROLS (non-fibromyalgia chronic pain)

Inclusion Criteria:

• Age 18 years or older
• Chronic non-cancer pain for at least 3 months with a defined nociceptive or neuropathic generator (e.g., radiologically or surgically documented degenerative, structural, or post-surgical musculoskeletal pain, or neuropathic pain with an identifiable neurological lesion or disease)
• Not meeting the 2016 ACR criteria for fibromyalgia
• Ability to understand and independently complete self-report questionnaires in Italian
• Willingness to provide written informed consent

Exclusion Criteria (parallel to cases):

• Diagnosis of fibromyalgia or another recognized nociplastic primary pain condition (e.g., primary chronic widespread pain)
• Active oncological disease or cancer-related pain
• Any current or past psychiatric diagnosis except Major Depressive Disorder and Panic Disorder
• Severe cognitive impairment precluding questionnaire completion
• Inability to understand or complete questionnaires in Italian

Note: ongoing pharmacological treatment for pain or mental health is not an exclusion criterion in either group; Major Depressive Disorder and Panic Disorder are recorded at baseline and used in covariate-adjusted and stratified analyses.

Adults attending Italian tertiary pain outpatient services. Cases are identified from fibromyalgia services; controls are identified among patients attending the same services for chronic non-cancer pain of defined nociceptive or neuropathic origin. Consecutive eligible patients are considered for enrollment.

Individual participant data (IPD) will not be shared publicly. Under Italian data protection regulations and the EU General Data Protection Regulation (GDPR), participant-level data from this study cannot be made publicly available. The working dataset is pseudonymized and held on secure institutional systems. De-identified data supporting the main findings may be made available from the corresponding author upon reasonable request, subject to a data-sharing agreement and compliance with applicable data-protection requirements.