This is to our knowledge the first prospective study that examines the performance of standardized PROs for both axial (axSpA) and peripheral (PsA) SpA in patients with pFM and compares them to patients with SpA and with or without concomitant FM in a real-life setting.
The basis of conducting the present study was recently published results showing that FM is a frequent finding not only in the general population23 but also appears frequently as a so-called ‘secondary’ FM as a concomitant clinical issue in chronic inflammatory rheumatic diseases38 and especially in axSpA23 or PsA39, the latter showing prevalences of around 20% of cFM in the examined cohorts. On the other hand, less patient-dependent evaluations such as ultrasound examinations showed recently that PsA patients are presenting with a higher number of involved entheses and patterns of entheseal involvement than patients with FM40. However, it was not investigated whether those evaluations discriminate polyenthesitis and FM in the same patient.
First data comparing the performance of some PROs before and after biologic drug treatment have already shown that cFM has a negative impact on the response to such treatment both in axSpA21,25 and PsA41 patients. Since all these studies were analysing data retrospectively based on existing information received from patient´s records, they also raised the need for a prospective evaluation on whether the clinical indices and especially the PROs validated in these indications are being influenced by cFM and, subsequently, how these data would also correspond in patients with primary FM diagnosis without any other RMD condition.
Our results, which included the currently most frequently used PROs in both axSpA and PsA clearly show that almost all of them need to be interpreted differently in the presence or absence of cFM. The only exceptions were ASDAS-CRP and duration of morning low back pain stiffness, which nevertheless still were slightly increased in patients with pFM. These findings strongly suggest to search for FM as an important comorbidity when evaluating these standard questionnaires in patients with axSpA and PsA both in daily practice and in the setting of clinical studies.
Our analyses showed that FM is significantly associated with worse scores on all PROs. The analysis of all individual questions of PROs clearly shows that the presence of fibromyalgia negatively affects all areas of patients' health and daily life. In particular, the feeling of fatigue (question 1 of the BASDAI), pain in the entheses and joints, as well as in the back and the physical function of the patients are significantly worsened by the co-existence of fibromyalgia. The other clinically relevant result is that questionnaires specifically developed for FM also showed high scores in patients with axSpA and PsA with cFM but, importantly, not in those without.
This study has some weaknesses but also some strengths. One could consider that the sample size of axSpA + and PsA+ (12 and 18 respectively) was too small to draw conclusions. However, such prevalence in the group of SpA patients presenting with cFM was expected, based on the existing literature42–44. In addition, the available studies21,25,26 so far have used the FiRST questionnaire to screen patients for FM at study inclusion. In our study, we based the diagnosis by the decision made by experienced rheumatologists and took also into account the revised ACR 2016 criteria, something that may also explain the small differences to previous results.
The strengths of the study are that our analyses were performed prospectively without any exclusion that might have biased the final outcome and on a representative total number of SpA and FM patients, in daily practice. Furthermore, the patients were eligible for treatment adaptation with high level of symptoms of clinical activity, which makes our results being closer to the clinical context on the influence of cFM on treatment decisions.