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We would like to thank Altobelli et al 1 for the interest they have expressed in our recently published article ‘Evaluation of the impact of concomitant fibromyalgia on tumor necrosis factor (TNF) alpha blockers’ effectiveness in axial spondyloarthritis (axSpA) : results of a prospective multicentre study’2 and the ARD editorial team to give us the opportunity to address their comments in this present letter.
First, we would like to emphasise that the purpose of this study was not to address the effectiveness of non-steroidal anti-inflammatory drugs (NSAIDs,) antidepressants or third-ladder analgesics, but to evaluate the effectiveness of TNF alpha blockers in an axSpA population and the potential impact of a concomitant fibromyalgia on such effectiveness. We agree that the evaluation of these other coprescription in patients with concomitant fibromyalgia would be of great interest, but this was not the aim of this study. Furthermore, the symptom severity score was not collected in this study.
Second, regarding their comment on stratification based on disease characteristics (in particular on radiographic and MRI sacroiliitis) when evaluating treatment effect, we would like to thank our colleagues for this comment. Indeed, this is exactly what was performed when analysing treatment effect on the multivariable analysis. First, we explored whether patients with/without concomitant fibromyalgia presented with different disease characteristics, and as reported in table 1 of the manuscript, we did not find any differences with regard to radiographic or MRI sacroiliitis when fibromyalgia was defined by the Fibromyalgia Rapid Screening Test (FiRST). However, some differences were observed for the ACR 1990 criteria and the Sust-FiRST definitions. Disease duration was not different across groups, regardless the definition. Nevertheless, since radiographic and MRI sacroiliitis have been consistently reported across studies as factors associated with treatment response, we included these variables in the multivariable model to assess the impact of fibromyalgia on the TNF blockers treatment effect, that is, the reported results of treatment effect are indeed adjusted by the presence/absence of both radiographic and MRI sacroiliitis, along with other factors (summarised in figure 2 of the manuscript) known to be associated with treatment response (ie, age, male gender, HLAB27+, smoking, elevated C-reactive protein (CRP), TNF blocker previous exposure).
Finally, we would like to thank our colleagues for their comment regarding on how enthesitis was assessed. Indeed, the potential overlap of axSpA-related pain at the entheseal sites and positive trigger points for fibromyalgia is a real concern in clinical practice. In the manuscript, as described in methods, we reported the history of peripheral enthesitis collected by clinical history during a face-to-face interview at the study visit by rheumatologists with an expertise in axSpA evaluation. Precisely, during the study visit, rheumatologists were asked to perform a physical examination to determine the presence/absence of tenderness on examination of 31 points. It was (on purpose) not clearly separated in the case report form that these 31 points included both the axSpA enthesitis points (13, according to the MASES index3) and the classic fibromyalgia trigger points (18 points).4 The evaluation of the agreement/overlap of both assessments is the objective of an ongoing ancillary analysis.
Handling editor Josef S Smolen
Contributors Both authors have equally contributed to the preparation of this response letter.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent Obtained.
Provenance and peer review Commissioned; internally peer reviewed.