Abstract
Anti-synthetase syndrome (ASS) is a rare inflammatory myopathy with a wide variety of clinical presentations. ASS-related interstitial lung disease (ASS-ILD) presents with rapid onset and progression, which could often be confused with other more common acute processes such as pneumonia, especially when ILD can be the sole manifestation. A woman in her 50s presented with recurrent dyspnoea for 2 months requiring multiple hospital admissions, and each time, she was diagnosed with multifocal pneumonia and treated with antibiotics. On admission, the evaluation revealed a markedly elevated creatine kinase level at 3258 U/L and a CT scan of the chest revealed worsening scattered ground-glass opacities. Given the concern for ILD as the cause of antibiotic failure, she underwent bronchoscopy with bronchoalveolar lavage which revealed non-specific interstitial pneumonia. A subsequent myositis panel revealed a positive anti-Jo-1 antibody, and she was diagnosed with ASS-ILD. She completed a course of intravenous immunoglobulin and methylprednisolone and experienced significant clinical improvement with the resolution of hypoxaemia and improved polyarthralgia.ASS could often be misdiagnosed as other more common acute lung processes, as a clinically subtle course can escape detection given its rarity, as well as its non-specific and highly variable presentations. This case highlights the importance of early suspicion and consideration of performing specific autoantibody testing when evaluating patients with a suspicion of undifferentiated autoimmune condition.