P005 When rheumatoid arthritis isn’t rheumatoid arthritis: a diagnostic journey

Background/Aims Inflamed joints are the mainstay of rheumatological conditions. Well established treatment guidelines and specialist early inflammatory arthritis clinics are widely implemented within secondary care. Refractory inflammatory arthritis often prompts clinicians to re-examine established diagnoses. VEXAS syndrome is a recently described auto-inflammatory disorder that can mimic classical rheumatological disease, leading to diagnostic delay. Methods Summary of Case: A 73-year-old presented with longstanding systemic inflammation and atypical arthritis. The initial diagnosis was polymyalgic-onset inflammatory arthritis alongside positive rheumatoid factor and anti-CCP antibodies. Results Despite multiple trials of DMARDs and biologics, including anti-TNF therapy, the patient showed poor response. They improved remarkably with corticosteroids but became dependent, requiring up to 40mg prednisolone daily during flares. Tapering resulted in symptomatic relapse. The clinical course became increasingly atypical. The patient developed recurrent fevers, severe fatigue, night sweats, painful subcutaneous nodules and constitutional decline. Haematological abnormalities manifested including macrocytosis, anaemia (Hb < 90 g/L) and intermittent pancytopenia, prompting haematology review and bone marrow biopsy. They suffered with recurrent ocular inflammation with bilateral episcleritis confirmed by ophthalmology. The painful skin lesions required dermatology input who agreed the presentation was not typical for inflammatory arthritis. Inflammation markers were consistently raised with CRP regularly above 190 mg/L and plasma viscosity >2. The overall pattern was no longer in keeping with classical inflammatory arthritis. The combination of steroid-responsive systemic inflammation, cytopenias and multi-organ involvement prompted reconsideration of the diagnosis. Genetic testing for the UBA1 mutation confirmed the presence of a somatic pathogenic variant, establishing a diagnosis of VEXAS syndrome (Vacuoles, E1 enzyme, X-linked, Auto-inflammatory, Somatic). Unfortunately, during follow up, the patient developed a suspected left posterior circulation stroke. Due to the thromboembolic risk associated with VEXAS syndrome, anticoagulation with edoxaban was initiated. Antiphospholipid testing was negative. Tocilizumab was initiated, in which significant clinical response was achieved within 6 weeks. Inflammatory markers normalised along with improvement of haemoglobin. The patient was also able to begin tapering corticosteroids without any relapse of symptoms. This demonstrates the role tocilizumab has with managing the condition. Conclusion This case illustrates the diagnostic challenges in a patient initially thought to have seropositive inflammatory arthritis. It highlights the importance of revisiting a diagnosis when patients fail to respond as expected and seeking expertise from other specialties in cases of unexplained systemic inflammation. Reporting such cases is valuable for learning to reduce misdiagnosing. Those newly diagnosed with VEXAS are thought to have a prognosis of 3 to 5 years due to historic diagnostic delay, however with wider awareness of this condition and better diagnostic ability, the prognosis can be greater. Disclosure L. Ibbotson: None. I. Ali: None.