Background Whether patient’s experience of fibromyalgia severity is related to measures of pain sensitisation assessed by quantitative sensory testing is not clear. How disease duration effects the relationship between disease severity and pain sensitisation changes is also unknown.

Objectives To examine the associations between pain sensitisation and fibromyalgia disease severity, as measured by the Polysymptomatic Distress scale (PDS) and Fibromyalgia Impact Questionnaire (FIQ). Secondly, to examine the impact of disease duration on the associations.

Methods Participants were recruited from referrals to a hospital clinic and the diagnosis verified by a specialist rheumatologist. Patients self-reported PDS and FIQ. Quantitative sensory testing included assessments of pressure pain threshold (PPT), temporal summation (TS) and conditioned pain modulation (CPM) were performed. PPT was tested 3 times at 5 predefined sites (a non-painful interphalangeal joint, dorsal radio-ulnar joint, lateral epicondyle of the elbow, middle surface of the trapezius muscle, and tibialis anterior muscle) using an algometer (FPIX 25). The pressure at which the patient first reported a slight pain was recorded, and the mean PPT values at each site and for all measurements (aggregated mean) were calculated. Lower PPTs indicate more pain sensitization. TS was estimated using probes of increasing weight that were tapped against the radioulnar joint. Pain was recorded on a numeric rating scale for the 1^st, 5^th, and 10^th tap of the probe that elicited a pain ≥ 4 on a 0-10 scale. The maximum difference in pain between the 1^st and either 5^th or 10^th tap was calculated, and an increase in pain during repetitive stimuli indicate TS. PPT was also tested before and after a conditioning stimulus with a blood pressure cuff around the contra-lateral arm, and the ratio of the PPTs (post:pre) was calculated. A positive ratio indicates adequate CPM.

Cut-offs of pain sensitization were defined as PPT < median, TS ≥ 2 and CPM <1. Disease duration was dichotomized at ≤ 5 vs. > 5 years. The associations between quantitative sensory testing and disease severity were explored in linear regression models adjusted for age, sex and body mass index and interactions with disease duration were explored.

Results A total of 78 patients (90% women, mean age 40.9 years (SD 7.3)) were recruited. In linear regression models, aggregated mean PPT was weakly associated with the PDS score, the FIQ total score and the pain, fatigue and depression components (Table 1). The mean PPTs from the trapezius and tibialis anterior muscles were also weakly but significantly associated with several components of the PDS and FIQ. TS was weakly associated with the anxiety and depression components of FIQ while there was no association between CPM and PDS or FIQ (Table 1). We found no evidence of disease duration being an effect modifier for the associations.

Conclusion In this cohort of patients with clinically verified fibromyalgia, pain sensitisation was weakly associated with self- reported disease severity. Disease duration did not impact on the relationship. Our results point to the multifactorial nature of the fibromyalgia symptom burden.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests Pernille Steen Pettersen: None declared, Trond Haugmark: None declared, Inger Jorid Berg: None declared, Tuhina Neogi: None declared, Hilde Berner Hammer Speakers bureau: AbbVie, Lilly, Novartis, UCB, Grant/research support from: AbbVie, Roche, Pfizer, Heidi A. Zangi: None declared, Ida K. Haugen Grant/research support from: Pfizer/Lily (paid to institution) and personal fees from Abbvie, Novartis and GSK, outside of the submitted work., Sella Aarrestad Provan Consultant of: Boehringer Ingelheim, Grant/research support from: Boehringer Ingelheim.