Short summary

SUMMARY Background: Chronic widespread pain is challenging in the management of the patient with rheumatoid arthritis (RA). However, pain is not always caused by inflammation but can be associated to central pain mechanisms as seen in fibromyalgia (FM). FM is characterized by widespread pain and tenderness; often accompanied by disturbed sleep, fatigue and multiple symptoms from various organ systems. Among patients with RA the prevalence of concomitant FM is reported to be 12-17% compared to 1-

Rationale

Managing chronic widespread pain in patients with rheumatoid arthritis (RA) presents a significant challenge. While inflammation is a common cause of pain in RA, it's important to recognize that pain can also stem from central pain mechanisms, as observed in fibromyalgia (FM). FM is characterized by widespread pain and tenderness, often accompanied by disrupted sleep, fatigue, and multiple symptoms affecting various organ systems. The prevalence of concurrent FM in RA patients is reported to be 12-17%, compared to 1-3% in the general population. Generally, the pain experienced by FM patients is attributed to lower pain thresholds resulting from abnormal central pain processing. It's possible that the pain reported by RA patients with coexisting FM could be explained by this phenomenon. Despite this, there remains limited understanding of RA patients meeting FM criteria. While studies of muscle pathology in FM patients haven't identified a histopathological basis for the pain experienced, an earlier study examining muscle changes in RA patients did uncover alterations potentially related to muscle pain. Additionally, small fiber neuropathy (SFN), a condition associated with autoimmune diseases, is believed to contribute to the pain observed in FM. Our goal is to investigate whether there is indeed a histopathological explanation for the increased prevalence of fibromyalgia in rheumatoid arthritis.

Description of the cohort

RA patients will be assessed in the daily clinic in Esbjerg and Odense and examined for concomitant fibromyalgia. Patients will then be invited to participate in the study. Inclusion will continue until 25 RA patients fulfilling fibromyalgia criteria have undergone the index tests, and thus, based on the expected prevalence, at least 25 RA patients not fulfilling fibromyalgia criteria have undergone the index tests.

Data and biological material

Muscle and skin biopsies

Collaborating researchers and departments

Department of pathology, Odense University Hospital

• Anne Bruun Krøigård
• Anne Ringer Ellingsen

Department of Neurology, Aarhus University Hospital.

• Pall Karlsson