Autoimmune Pulmonary Alveolar Proteinosis Triggered by Salazosulfapyridine in a Patient With Rheumatoid Arthritis: A Case Report

A 91-year-old woman diagnosed with rheumatoid arthritis (RA) in her 40s achieved disease stabilization after salazosulfapyridine (SASP) treatment. In May 2025, chest computed tomography (CT) revealed bilateral ground-glass opacities with interlobular septal thickening, presenting a crazy-paving pattern. She was diagnosed with autoimmune pulmonary alveolar proteinosis (aPAP) based on positive serum anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) antibodies and periodic acid-Schiff (PAS)-positive fluid accumulation in the alveoli identified on transbronchial lung biopsy (TBLB). The development of aPAP is considered extremely rare in patients with RA, as the disease is typically characterized by elevated GM-CSF activity, creating a pathological paradox. Previous reports have revealed that almost all patients with aPAP and RA receive SASP treatment. We hypothesized that aPAP associated with RA developed due to a dual suppression of GM-CSF: drug-induced inhibition of GM-CSF at the alveolar level and acquired production of anti-GM-CSF antibodies.