AAPT Fibromyalgia Criteria and Concomitant Musculoskeletal Diagnoses in a Referral-Based Pain Clinic Cohort: A Retrospective Pilot Study

Background/Objectives: Fibromyalgia (FM) is diagnosed using symptom-based criteria, and clinician-assigned labels may diverge from standardized classification frameworks. FM may also coexist with musculoskeletal and other pain-related conditions. We determined the proportion of patients in a combined referral-based cohort who fulfilled the 2019 ACTTION-American Pain Society Pain Taxonomy (AAPT) criteria after retrospective record-based adjudication and described documented concomitant musculoskeletal or pain-related diagnoses and symptom burden according to AAPT status. Methods: This retrospective, single-center cross-sectional pilot study included consecutive adult outpatients evaluated in a tertiary pain unit between January and April 2026 after referral for suspected FM or with a previous clinician-assigned FM diagnosis. AAPT classification was reconstructed from available longitudinal clinical documentation; the historical look-back varied by record availability and extended approximately 8–10 years in some patients. Results: Among 76 patients (96.1% female), 28 fulfilled the AAPT criteria (36.8%; 95% CI, 26.9–48.1). At least one documented concomitant musculoskeletal or pain-related diagnosis was recorded in 25/28 AAPT MET patients (89.3%; 95% CI, 72.8–96.3) and 26/48 AAPT NOT MET patients (54.2%), corresponding to a crude, unadjusted OR of 7.05 (95% CI, 1.87–26.54; p = 0.002). This association may partly reflect criterion-related overlap and differential diagnostic ascertainment. Exploratory analyses suggested greater symptom and affective burden in the AAPT MET group, whereas NRS pain intensity did not differ. Conclusions: Approximately one-third of this combined referral-based cohort fulfilled the AAPT criteria on retrospective adjudication. Documented concomitant musculoskeletal or pain-related diagnoses were common, but the observed association with AAPT status should not be interpreted as independent or causal. Standardized classification and multidimensional clinical pain phenotyping provide complementary information in chronic widespread pain.