A35-17 A Case of Anti-Synthetase Syndrome: When Pneumonia Isn’t Pneumonia

Abstract Introduction Anti-synthetase syndrome (ASS) is an uncommon autoimmune disorder defined by antibodies against aminoacyl-tRNA synthetases, most frequently anti-Jo-1. The clinical spectrum includes interstitial lung disease (ILD), inflammatory myopathy, arthritis, Raynaud’s phenomenon, and “mechanic’s hands.” ILD accounts for most of the morbidity and can precede extra-pulmonary symptoms, often mimicking pneumonia and delaying recognition. Early treatment is crucial to prevent irreversible fibrosis, yet balancing adequate immunosuppression with infection risk remains a major challenge. Case Description A 63-year-old man with chronic kidney disease, a thrombus in the ascending aorta on anticoagulation, and new-onset proximal muscle weakness presented with worsening dyspnea, as well as concern for hemoptysis versus hematemesis. Patient required high-flow nasal cannula. Chest CT angiography revealed bibasilar infiltrates without effusion, and the patient was empirically treated for presumed bilateral pneumonia and sepsis. Previous records showed a positive ANA (1:160, speckled). Workup in the hospital revealed elevated creatine kinase (7,265 IU/L) and aldolase (40.4 U/L). Patient received 3 days of pulse dose steroids 1 g daily and continued on high-dose methylprednisolone (1 mg/kg) for suspected inflammatory myositis. Ganciclovir was started for Cytomegalovirus (CMV) viremia. His myositis antibody panel returned positive for anti-Jo-1 antibody (132 SI), confirming anti-synthetase syndrome. Since the patient was born in Vietnam and the initial QuantiFERON-TB Gold test results were inconclusive, bronchoscopy with bronchoalveolar lavage (BAL) was performed to rule out tuberculosis, and the workup was negative. After CMV PCR became undetectable and TB was excluded, immunosuppression was escalated with rituximab (1,000 mg IV × 2 doses, 2 months apart) and mycophenolate mofetil (titrated to 1 g twice daily). Prophylaxis with trimethoprim-sulfamethoxazole and valganciclovir was initiated. Subsequent imaging revealed complete resolution of the interstitial infiltrates, allowing the patient to be gradually weaned off supplemental oxygen. Discussion This case illustrates how anti-synthetase-related ILD can initially resemble severe pneumonia. Early recognition of the autoimmune origin and deliberate sequencing of therapy (treating active infections before introducing combination immunosuppression) were key to recovery. Initiating corticosteroids followed by rituximab and mycophenolate, supported by comprehensive infection screening and prophylaxis, underscores the value of multidisciplinary coordination in restoring lung function and preventing relapse in this complex autoimmune disease. This abstract is funded by: None