B41-44 Examination of HRCT Findings in Fibrotic Interstitial Pneumonia With Positive for Specific IgG Antibody to Bird Antigen

Background The measurement of serum bird-specific IgG has become increasingly common in clinical practice to hypothesise the causative antigens in chronic fibrotic hypersensitivity pneumonitis (HP). However, there is limited research correlating these findings with imaging characteristics. Objective To investigate the imaging findings and clinical background of patients with chronic interstitial pneumonia who are positive for serum bird-specific IgG. Methods This retrospective study included patients who tested positive for serum bird-specific IgG at our institution between February and September 2024. We reviewed the patients’ bird exposure history and high-resolution computed tomography (HRCT) findings to assess the correlation between these factors. Results A total of 91 patients underwent serum bird-specific IgG testing, of whom 37 tested positive. The median age of the 37 positive patients was 75 years (range, 56-88). The cohort comprised 13 females and 24 males, with 21 patients having a smoking history. The diagnoses of interstitial lung disease prior to IgG testing were as follows: 20 cases of idiopathic interstitial pneumonia, 5 cases of fibrotic hypersensitivity pneumonitis, 9 cases of collagen vascular disease-related interstitial pneumonia, and 3 cases of drug-induced pneumonitis. Of the 37 IgG-positive patients, 10 reported current exposure to birds, while 5 had a history of bird keeping but no current exposure. HRCT findings were classified according to the ATS/JRS/ALAT guidelines for fibrotic HP: 11 patients had a Typical HP pattern, 6 had a Compatible with HP pattern, and 20 had an Indeterminate for HP pattern. Of the 10 patients with current or past bird exposure, 5 had a Typical HP pattern, while 5 had an Indeterminate for HP pattern. Conclusions HRCT findings in patients with serum bird-specific IgG positivity and fibrotic hypersensitivity pneumonitis are heterogeneous. Clinical judgement, including a detailed history of bird exposure, is essential in diagnosing bird-related fibrotic hypersensitivity pneumonitis.