B43-13 Diagnostic Difficulty of Anti-synthetase Syndrome in a Previously Healthy Female

Abstract Background Anti-synthetases syndrome (ASyS) is an idiopathic, autoimmune myopathy with targets against aminoacyl-tRNA synthetase (ARS). Anti Jo-1 is the most prevalent anti-ARS antibody. ASyS often presents with a triad of myositis, inflammatory arthritis, and interstitial lung disease. Other common symptoms include fevers. 1 Notably, among anti-Jo-1 positive patients, 80-90% of patients will develop ILD at some point. Presentation An active 58-year-old woman with a remote history of tobacco use presented initially with a four-month history of progressive shortness of breath, dry cough, exercise intolerance, and fatigue. Given symptoms and X ray showing consolidation, she was initially treated for presumed pneumonia and allergies with multiple antibiotic courses (amoxicillin, augmenting, azithromycin, doxycycline, cefdinir), several short courses of prednisone, and both inhaled steroids and albuterol. No treatment resulted in lasting improvement. Imaging over three months demonstrated persistent, bilateral, ground glass opacities (GGO) and areas of consolidation involving all lobes. Lab testing revealed negative ANA, RF, CCP, normal ESR, CRP, and elevated aldolase. After discontinuing prednisone, she developed polyarticular joint pain and stiffness in the hands, shoulders, and knees. She was admitted three months after initial presentation for worsening hypoxemia with repeat CT showed progression of GGOs. She underwent VATS with wedge resections of the lung that showed organizing pneumonia with intra-alveolar macrophages, without granulomas or fibrosis. Given the biopsy findings and progressive course, she was diagnosed with organizing pneumonia of unclear etiology. She was discharged with a prolonged course of corticosteroids and myositis panel pending In the outpatient setting, the Anti-JO-1 antibody test returned positive, indicating myositis, aligning with joint and lung symptoms. The patient was ultimately diagnosed with interstitial lung disease in the setting of anti-Jo1 positive ASyS and is being treated with prednisone, with authorization for rituximab therapy pending. Discussion This case highlights an atypical and diagnostically challenging presentation of ASyS in which the initial symptoms in this highly active patient mimicked community acquired pneumonia rather than an autoimmune process. The gradual onset of ILD preceding any myositis or arthritis, in conjunction with negative ANA, RF, and CCP delayed recognition of the underlying autoimmune etiology. Additionally, her biopsy showed organizing pneumonia rather than the more typical nonspecific interstitial pneumonia pattern, more often seen in ASyS. This patient’s presentation underscores a diagnostic challenge that ASyS can initially manifest as isolated or predominantly ILD, with classic musculoskeletal or systemic findings emerging only later in the disease course. This abstract is funded by: None