The study confirms that coexistent fibromyalgia in spondyloarthritis might impact the patient-reported outcome indices for disease activity and function and retention rate of TNFi treatment.

Spondyloarthritis (SpA) is a disease that includes a spectrum of chronic inflammatory entities involving axial skeleton (sacroiliac joints and spine) and peripheral joints, and sharing a number of clinical features such as arthritis, enthesitis, uveitis, dactylitis, psoriasis, and inflammatory bowel disease with a common genetic background, the human leukocyte antigen (HLA) B27. In 2009, Assessment of the Spondyloarthritis International Society (ASAS) proposed a new set of classification criteria with the aim of recognizing patients with early axial SpA (axSpA) including for the first time the imaging of the sacroiliac joints (SIJ) by magnetic resonance imaging (MRI) and abnormal C-reactive protein (CRP), and another set for SpA patients with predominantly peripheral manifestations (e.g., peripheral arthritis, enthesitis, and dactylitis). The axSpA criteria allow the classification of patients with chronic back pain lasting for ≥3 months and occurring before 45 years of age, through two arms: the imaging arm in which patients present with sacroiliitis (either on radiographs or MRI) plus at least one additional SpA feature, and the clinical arm in which patients need to be HLA-B27 positive and present with two or more SpA characteristics. However, the clinical arm has been criticized and is not well-recognized by health authorities.

Rationale behind research:

Fibromyalgia (FM) can co-exist with SpA leading to diagnostic and treatment dilemmas, especially in the presence of enthesitis. Thus, this study was conducted to estimate the prevalence of FM in SpA and to compare the clinical/disease features and TNF inhibitors (TNFi) in patients with/without FM.

Objective:

a) To estimate the prevalence of FM according to the FiRST in a population of patients with SpA and to compare the prevalence with regard to the arm fulfilled within the axial criteria (i.e., the imaging and clinical arms)

b) To compare the demographics/disease features, and TNF inhibitor (TNFi) treatment in terms of initiation and first TNFi retention rate, in patients with and without FM

Study outcomes

Prevalence of FM in SpA:

FM was defined if the score was ≥5/6 in the FIRST questionnaire. Medical files of each patient who completed the FiRST questionnaire were reviewed by two external investigators. The following information was collected: age, gender, smoking status (past, current, never), body weight and height, and the date of SpA diagnosis, all available items permitting the calculation of the fulfilment of the ASAS criteria; BASDAI, global visual analog scale (VAS) according to the patient, presence and number of current swollen joints diagnosed by a physician and CRP at the day of the visit were collected, and severity of the disease evaluated at the time of the visit using the BASFI.

Comparison of clinical/disease features and TNF Inhibitors:

SpA treatments since disease onset including information on non-steroidal anti-inflammatory drugs (NSAIDs), conventional disease modifying antirheumatic drugs (cDMARD), and the type and number of TNFi, number of switches, start/end date and reason for discontinuation for each TNFi. Information on past or current use of psychotropic medications (i.e., myorelaxants, antidepressants, or anxiolytics), strong opioids, and history of depression were collected.

Outcomes

• Prevalence of concomitant FM was greater in the group not fulfilling the ASAS criteria, although this difference was not statistically significant (21.1% vs. 30.0%, not significant). More interestingly, no differences in the prevalence of FM were observed in the group of patients fulfilling the imaging and clinical arms of the ASAS criteria for axSpA (21.3% vs. 19%, not significant).
• FM+ and FM- groups were similar in terms of age, mean age at disease onset and smoking status. However, patients fulfilling the FM+ definition presented more frequently with enthesitis (59.5% vs. 39.0%, p = 0.01), a higher total BASDAI (4.7 (±2.3) vs. 2.6 (±1.9), p <0.01), higher global VAS (5.9 (±2.4) vs. 3.0 (±2.5), p <0.01) and higher BASFI (4.8 (±2.7) vs. 2.0 (±2.3), p <0.01). No significant differences were found for treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) and conventional disease-modifying antirheumatic drugs (cDMARDs); as expected, the percentage of patients with either history of depression, or use of psychotropic medication or strong opioids was significantly higher in the FM+ group (67% vs. 35%, p <0.01). 
• The percentage of patients ever exposed to TNFi did not differ between the FM+ vs. FM– groups (79% vs. 70%, respectively, not significant), whereas the percentage of switchers was significantly higher in the FM+ group (15.2% vs. 4.0%, p = 0.03). Mean duration of the first TNFi was significantly shorter in FM+ group (1.7 (± 2.4) vs. 3.5 (± 4.0) years, p <0.01).
• Retention rate of the first TNFi after 2 years was significantly shorter in FM+ group: 28.1% (95% CI 12.5; 44.0) (n = 9) vs. 41.7% (95% CI 32.2; 51.3) (n = 43) of patients were still on TNFi treatment after 2 years in FM+ and FM– groups, respectively (p <0.01).
• Univariate Cox analysis identified FM (hazard ratio (HR) 1.8, 95% CI 1.1; 3.0), peripheral involvement (HR 1.6, 95% CI 1.0; 2.6) and history of depression or psychotropic medications or strong opioids intake (HR 0.6, 95% CI 0.4; 0.9) as associated factors for discontinuation of the first TNFi; however, on multivariate analysis only FM (HR 1.7, 95% CI 1.0; 2.9) and peripheral involvement (HR 1.6, 95% CI 1.0; 2.6) were independently associated with discontinuation of the first TNFi. Reasons for discontinuation of each TNFi were similar percentages in the two groups (p value not significant), inefficacy being the most frequent reason in the total population.
  

In this study, similar percentages of FM in the different subgroups of the ASAS classification criteria might be a good argument in favor of the validity of these criteria, and in particular of the clinical arm. The coexistence of FM might impact the score of instrument used to evaluate disease activity and severity, particularly in the patient-reported scores, and therefore might complicate the evaluation of treatment response. The implementation of the FiRST questionnaire might be helpful in clinical practice, especially in the presence of enthesitic symptoms.

These results are consistent with the previous studies. However, this is the first study aiming to evaluate the prevalence of FM according to the fulfilment of the ASAS classification criteria and its impact on TNFi treatment.