• fibromyalgis/pain syndromes
• disease activity
• treatment
• spondyloarthritis

We read with great interest the study published by Moltó et al on the impact of concomitant fibromyalgia (FM) on tumor necrosis factor (TNF) alpha blockers’ effectiveness in axial spondyloarthritis (axSpA).1 Indeed, this is a challenging problem in daily practice, especially considering the difficulties in differentiating enthesitis and FM symptoms.2 Therefore, we would like to raise some issues that need clarification in order to better understand the relevance of the study.

In the published paper, data on the history of antidepressant, third-ladder analgesic and nonsteroidal anti-inflammatory drug (NSAID) intake in patients enrolled are extensively reported. The results indicate that the use of antidepressants was significantly greater in patients with FM according to FiRST,3 American College of Rheumatology (ACR) 1990 criteria4 and sustained FiRST. However, no data are reported regarding the outcome of these therapies on FM symptoms, which could be evaluated by using the symptom severity score.5 We believe that this issue could significantly impact the patient-reported outcomes.

We also consider of great relevance the stratification of patients with axSpA in terms of presence or absence of chronic damage. In the paper, the authors report data on X-ray and MRI sacroiliitis. This classification implies the inclusion in the study of different subgroups of patients with axSpA, since those with X-ray sacroiliitis are likely to be patients with ankylosing spondylitis (AS) with a longer disease duration, while patients with MRI sacroiliitis might have been affected by non-radiographic axSpA. This observation deserves attention based on the finding that patients with established AS may fulfil FM criteria more often than patients with non-radiographic axSpA, probably due to the severity and duration of chronic pain.6 This aspect should be considered when evaluating the response to TNF alpha blockers, being able to affect patient-reported outcomes.

Finally, the results of the study show a higher percentage of the history of peripheral enthesitis in patients with FM. However, the authors do not specify how the enthesitis was diagnosed (ie, by clinical evaluation or imaging tools) and in which site.7 Again, this is a crucial point since patients with FM experience widespread pain and have tender points that could simulate enthesitis symptoms if detected only on the basis of clinical examination in the absence of an instrumental assessment8 (see online supplementary table S1).

In conclusion, we appreciate the issue addressed by the authors in their paper, which provides precious information for a more aware treatment of patients with axSpA and concomitant FM. We believe that an answer to our comments would help readers better understand the relevance of this study. Certainly, it is important to face the challenge of a correct interpretation of disease activity indexes including patient-reported outcomes in patients with axSpA and concomitant FM in order to avoid unwarranted use of medications.