Abstract Introduction Idiopathic inflammatory myopathies (IIM) are heterogeneous rheumatic diseases with variable muscle and extra-muscular involvement. Diagnosis often depends on clinical features and myositis-specific antibodies, which help guide management and prognosis. Among these, the OJ autoantibody targets aminoacyl-tRNA synthetase and is associated with antisynthetase syndrome (ASSD), a condition that can present with rapidly progressive interstitial lung disease (ILD). Detection of anti-OJ remains challenging, as commonly used commercial assays have limited sensitivity, and testing may be unavailable. In patients with rapidly progressive ILD, clinicians must maintain a high suspicion for ASSD, since rare antibodies like anti-OJ may be missed, delaying diagnosis and treatment. Case Our patient is a 77-year-old woman with coronary artery disease, heart failure with preserved ejection fraction, and chronic ILD on 4-5 L/min home oxygen presented with worsening dyspnea and leg edema and was admitted for presumed heart failure exacerbation. Despite antibiotics and diuresis, hypoxia persisted. Chest CT revealed diffuse ground-glass opacities (GGO) with progressive fibrotic reticulations and traction bronchiectasis concerning worsening ILD Image 1. Review of prior admissions showed three similar episodes over six months, each responsive to steroids. Serial CT scans demonstrated rapid progression of diffuse GGOs and peripheral reticulations. Previous ILD serologies showed positive antinuclear antibodies and anti-Ro but negative myositis panels. Due to concern for rapidly progressive ILD, repeat testing was obtained and returned positive for anti-OJ antibody. She was ultimately diagnosed with antisynthetase syndrome and started on steroids and rituximab with improvement in her symptoms. Discussion Our case demonstrates how diagnosing anti-synthetase syndrome requires high clinical suspicion as much as understanding the limitations of available assays. Although our patient’s presentation was consistent with myositis-associated interstitial lung disease, the initial workup was non-diagnostic, highlighting the limited sensitivity of standard available assays. Commercial platforms (e.g., Quest, ARUP) primarily use ELISA or line-blot testing, which, while highly specific (∼95%), demonstrate poor sensitivity (∼20%) for rare antibodies such as anti-OJ due to loss of native antigen structure. In contrast, immunoprecipitation preserves antigen conformation and yields markedly higher sensitivity (100%) and specificity (93.8%). In the context of RP-ILD, immunoprecipitation assays should be considered the preferred modality for detecting antisynthetase antibodies, given their superior sensitivity and specificity, thereby facilitating accurate exclusion or confirmation of antisynthetase syndrome. This abstract is funded by: none
Situt et al. (Fri,) studied this question.