P105 Auto-inflammatory idiopathic serositis: an under-characterised phenomenon?
Authors: Pillai Kavya , Perera James , Kurzeja Dominik , Amin Sanaah , Choudhury Maahia , Stratton Richard 
Published: April 2021

Abstract
Background/Aims
Serositis is a broad term encompassing inflammation of the pericardium, pleural or peritoneum. Serositis can be secondary to various conditions ranging from systemic lupus erythematous, inflammatory bowel disease and familial Mediterranean fevers. Due to the multitude of precipitating causes, idiopathic serositis is a diagnosis of exclusion and requires extensive medical work-up. This case series details patients who have developed inflammatory serositis without a clear underlying precipitating cause over the past 12 years at the Royal Free Hospital, a tertiary rheumatology centre based in London.
Methods
Patients were identified retrospectively through electronic records by searching through clinic letters and discharge letters from 2008 to 2020. Search terms including serositis, pericarditis, pleuritis and peritonitis were used. Data collected included their key demographic details, laboratory and pathology investigations as well as the course of treatment and follow up data, including rate of recurrence, complication and survival outcomes. Patients with underlying rheumatological, immunological, or malignant causes were excluded.
Results
Four hundred and twenty patients over 12 years with serositis were identified with 22 patients classified as idiopathic, auto-inflammatory serositis. Patient demographics indicate a 5:2 female preponderance for the condition with an average age of 61 (range 19-87) and Caucasian ethnicity (68.2%, 15/22). Patients were investigated for underlying causes, including screening for infection and autoimmune conditions, and imaging was performed including computer tomography and positive emission tomography. Autoimmune screening revealed weakly positive autoantibodies of low sensitivity (anti-neutrophil antibodies and rheumatoid factor) in 18.2% (4/22) patients. Treatment options varied, typically with immunosuppression being initiated acutely with steroid therapy, either oral prednisolone or intravenous methylprednisolone, depending on severity of disease presentation before progression to steroid-sparing agents, including mycophenolate motefil (50%, 11/22), cyclophosphamide (13.6%, 3/22) and azathioprine (9.1%, 2/22). Other therapies including colchicine (40.9%, 9/22) were used. Relapse was relatively uncommon once patients were established on steroid-sparing agents (21.7%, 5/22). However, Anakinra (interleukin-1 receptor antagonist) was initiated in patients with recurrent relapses (9.1%, 2/22) with good response. One patient died through bronchopneumonia following cyclophosphamide therapy. Of note, pericardial stripping was required in patients with haemodynamic compromise during admission in 3/22 (13.6%) with 1 patient in this subset subsequently requiring Anakinra therapy.
Conclusion
Auto-inflammatory idiopathic serositis appears to be distinct category of serositis affecting predominantly middle aged to elderly female Caucasian patients, without underlying connective tissue disease, requiring prolonged therapy with immunosuppressive agents, which can be characterised by involvement of multiple serous membranes and/or recurrent episodes of serositis. This condition appears to respond well to immune suppression with steroids, steroid-sparing agents and Anakinra. Further work will be required to characterise and classify this condition and to establish treatment guidelines.
Disclosure
K. Pillai: None. J. Perera: None. D. Kurzeja: None. S. Amin: None. M. Choudhury: None. R. Stratton: None.