Concomitant Diagnosis of Fibromyalgia and Ankylosing Spondylitis: Relation to Clinical Features and Plasma Pentraxin -3 Level

Background: Ankylosing spondylitis (AS) is a chronic systemic inflammatory rheumatic disease that specifically affects the spine and sacroiliac joint. AS diagnosis is often delayed in the clinical practice and this delay may cause the patients to miss the chance of early treatment. Fibromyalgia (FM) is a frequently encountered clinical syndrome, fibromyalgianess is a term used when patients who are diagnosed with inflammatory arthropathies meet the criteria for FM syndrome as shown in rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Sjogren syndrome, and AS. Objectives: We aimed primarily to assess the frequency of concomitant diagnosis of FM syndrome in AS patients and study its impact on clinical disease aspects. Secondary, our aim extended as a preliminary pilot study to assess the Plasma Pentraxin-3(PTX-3) as a potential marker for the diagnosis of FM syndrome in AS patients. Methods: Plasma PTX-3 in 61 AS patients was compared to 60 matched controls. FM was diagnosed by FM Rapid Screening Tool. Bath AS disease activity index (BASDAI) and AS disease assessment score using C-reactive protein (ASDAS-CRP), Bath AS functional impairment index (BASFI), Bath AS metrology index (BASMI), AS quality of life (ASQoL) scale, Beck Depression Inventory, and Bath AS Radiology Index (BASRI) were assessed. Results: The patients were categorized into two groups according to the concomitant diagnosis of FM syndrome. Group I included 14 (22.9%) AS patients who fulfilled the clinical diagnosis of FM syndrome. Group II included 47 (77.1%) AS patients without FM syndrome. AS patients with FM (Group I) had significantly(p<0.001) increased an average of ages, disease duration, diagnostic delay of AS, switching of bDMARDs, morning stiffness duration, ASDAS-CRP, BASFI, ASQoL score, BASDAI (p=0.008), and BDI score (p=0.005) compared to AS patients without FM (Group II). PTX-3 levels were significantly (p<0.001) higher in Group I (p<0.001) (median, 0.23; IQR, 0.15-0.41 ng/ml) than Group II (median, 0.13; IQR, 0.035-0.21ng/ml) which showed no significant differences (p>0.05) compared to the controls. PTX-3 levels had significant positive correlations (p<0.05) with disease duration, BASFI, and ASQOl. Age, female sex, switch of biologic, ASDAS CRP, and PTX-3 were significant predictors of FM in AS patients. Conclusion: These results indicate that concomitant FM is a significant problem in patients with AS and its presence is associated with higher disease activity, impaired function as well as an overall negative impact on QoL. Easy scanning of suspicious cases of FM with FiRST questionnaire can be done in daily practice. PTX-3 is more or less accurate as the clinical features to improve the diagnostic certainty of FM in the presence of AS with a proven sensitivity of 62.3%, a specificity of 90%, a positive predictive value of 82.75%, and a predictive value of 73.9%.