SAT0504 STING-ASSOCIATED VASCULOPATHY WITH ONSET IN INFANCY (SAVI SYNDROME) CAN MIMIC JUVENILE IDIOPATHIC ARTHRITIS.

Background:STING-associated vasculopathy with onset in infancy (SAVI syndrome) can mimic Juvenile Idiopathic Arthritis.Objectives:The aim of this study is to describe a detailed cohort of patients with SAVI syndrome and highlight the similarity, in some cases, of the phenotype of this disease with Juvenile Idiopathic Arthritis.Methods:3 patients diagnosed with SAVI syndrome from the institution Hospital Universitari Vall d’Hebron were recruited. Written informed parental consent was obtained for the use of clinical data and pictures reported. Demographic, clinical, analytical, lung function and previous and current treatment are described.Results:Patient 1, a 11-year-old boy, was identified to carry a de novo p.V155M mutation in TMEM173. He presented at first month of life with recurrent bronchial infection and skin vasculitis lesions in nose, cheeks and toes. Arthritis affected hands, toes and knees but no erosions were found at X-Ray. Fever was not reported. High-resolution computed tomography (HRCT) of the lungs identified a nonspecific interstitial pneumonia (NSIP) and a lung biopsy showed lymphoid hyperplasia. Elevated inflammatory markers were reported and rheumatoid factor (RF), ACPA antibodies and antinuclear antibodies (ANA) were also positive. At the age of 6 years Ruxolitinib (RX) was introduced at the initial dose of 5 mg twice daily with an improvement of skin disease and lung function. Arthritis was well controlled and RX was well tolerated.Patient 2, a 17-year-old girl, was identified to carry a de novo p.V155 mutation in TMEM173. She presented at the age of 3 with a severe polyarthritis of large and small joints. No fever, skin or respiratory symptoms were reported at the beginning of the disease. Laboratory tests were positive for RF and ACPA antibodies. She was diagnosed with Polyarticular JIA and was treated with steroids and Methotrexate without improvement. Few months later she reported dyspnoea with recurrent bronchial infections. HRCT showed NSIP and lymphoid interstitial pneumopathy was found at the lung biopsy. RX was initiated at the age of 17 years but at this time lung fibrosis was stablished. Moreover, RX was not well tolerated due to headache. She requires continuous domiciliary oxygen and has been included to lung transplant.Finally, patient 3, a 29-year-old man, was recently diagnosed with a de novo p.V155 mutation in TMEM173. He presented at the age of 7 years with symmetrical polyarticular arthritis after a bronchial infection that course with fever. No skin manifestations were objectified. Autoimmune lab test was positive for RF, ACPA, and ANA. With the diagnosis of Polyarticular JIA he received different treatments with no response. Due to recurrent bronchial infections a HRCT was performed showing an ILD at bases and follicular bronchiolitis with NSIP pattern in a lung biopsy. Functional tests were worsening without any response to different treatments. SAVI syndrome was suspected, and genetic test was performed with positive result. RX was initiated but compliance was not goodConclusion:SAVI syndrome is a rare monogenic autoinflammatory disease with few cases reported in the literature. Disease phenotype could be different in every patient, with no presence of skin vasculitic lesions or fever. Patient 2 and 3, in contrast with patient 1, had severe articular and lung manifestations with no skin involvement. Furthermore, lab tests were positive for RF and ACPA and were misdiagnosed as JIA so genetic test was performed later in the follow-up. Being aware of the distinct phenotype of the disease could help the clinicians to make a PRONTO diagnostic and reassess the patients with these presentations that not respond well to conventional treatments.References:[1]Liu Y, et al. Activated STING in a vascular and pulmonary syndrome. N Engl J Med. 2014 Aug 7;371(6):507-518.Disclosure of Interests:None declared