The ”Joint criteria” for fibromyalgia diagnosis in rheumatoid arthritis patients: validation and assessment of disease activity

The objectives of this study where to validate the ”joint criteria” for fibromyalgia (FM) diagnosis represented by the difference between tender joint count (TJC) and swollen joint count (SJC) in rheumatoid arthritis (RA) patients undergoing biological treatment and examine clinical and ultrasound parameters in patients with and without FM. Patients and methods. RA patients on biological treatment were included during one month. ROC analysis was used to determine whether the ”joint criteria” could differentiate between patients with associated FM and those without. The disease activity score in 28 joints (DAS28) was calculated and ultrasound (US) examination was performed using the 7 joint score. Results. 39 patients were included. The ”joint criteria” had a sensitivity of 85% and specificity of 87% for FM diagnosis for a difference of ≥ 6 between TJC and SJC. Nine (23%) patients were diagnosed with FM using these criteria. Patients with RA-FM had higher values compared to RA for the DAS28 (5.1 vs 3.3, p= 0.01), TJC (12 vs 3, p < 0.001) and patient global assessment (PGA) (58 vs 41, p < 0.001), but similar values for SJC (1 vs 2, p=0.6), erythrocyte sedimentation rate (ESR) (27 vs 22, p= 0.21), C reactive protein (CRP) (8.6 vs 8.4, p= 0.6) and ultrasound parameters (Gray Scale synovitis 2.6 vs 3.8, p= 0.9; Power Doppler synovitis, 1.2 vs 1.6, p= 0.5; Gray Scale Tenosynovitis 0.4 vs 0.3, p=0.3; Power Doppler Tenosynovitis, 0.3 vs 0.2, p=0.08). Discussions. Our findings confirm previous published data on RA-FM diagnosis and disease characteristics on a sample of RA patients on biological treatment. The ”joint criteria” is a feasible tool and could easily identify patients with RA and FM in order to improve disease management. Conclusions. A difference of ≥ 6 between TJC and SJC is diagnostic of FM in RA patients. Patients that satisfy this criteria have higher DAS28 scores, TJC, PGA but similar SJC, ESR, CRP and US scores compared to RA patients without FM.