B43-37 Evolving Interstitial Lung Disease (ILD): From Hypersensitivity Pneumonitis Mimic to Connective Tissue Disease-ILD

Abstract Introduction Connective tissue disease-ILD (CTD-ILD) can present with varied and evolving phenotypes which may mimic other diffuse parenchymal lung diseases, including hypersensitivity pneumonitis (HP). Early seronegative cases often pose a diagnostic challenge, as ILD may initially be the only manifestation before later evolving to reveal autoimmune serologies consistent with Connective Tissue Disease (CTD). Case Description A 59 year old woman with hypertension and type 2 diabetes developed progressive dyspnea, cough, and hand swelling after cleaning an old house that contained dust, mold, and mouse droppings. She also reported pleuritic chest pain, lower extremity edema, and joint stiffness. She was treated empirically with steroids and two courses of antibiotics for presumed pneumonia without improvement and was subsequently admitted for evaluation. CTA chest showed multifocal interstitial infiltrates without pulmonary embolism; cardiac work-up was normal. Given her environmental exposure and imaging pattern, hypersensitivity pneumonitis or organizing pneumonia was suspected. Initial ILD work-up showed mildly elevated C-reactive protein (2.9 mg/dL) with negative autoimmune and myositis panels. Rheumatology evaluation did not identify a specific Connective Tissue Disease. Serial HRCTs showed persistent peribronchial and basilar opacities with no interval improvement, prompting initiation of mycophenolate mofetil for suspected CTD-ILD. Follow-up serology at a tertiary center demonstrated ANA 1:80 (cytoplasmic, speckled) and anti-SSA-52 positivity, suggesting an evolving myositis-spectrum or amyopathic CTD-ILD. Discussion This case illustrates how, even in the absence of a confirmed systemic rheumatologic disorder, patients may initially present with ILD as the first and only manifestation of evolving CTD-ILD. Cavagna et al. reported that up to one-third of antisynthetase-spectrum cases develop new systemic features months or years after isolated ILD onset. The patient’s environmental exposure, HP-like imaging, and negative serologies initially obscured the underlying disease, while later anti-SSA-52 positivity was consistent with a myositis-spectrum or amyopathic CTD-ILD. Joy et al. found that ANA and anti-SSA-52 positivity strongly correlate with ILD development across CTDs. This highlights the evolving nature of CTD-ILD and the need for longitudinal reassessment when ILD persists despite standard therapy. This abstract is funded by: None