Beyond Pneumonia: Autoimmune Pulmonary Alveolar Proteinosis in a Pediatric Patient.

Pulmonary alveolar proteinosis (PAP) is a rare pediatric lung disorder marked by the accumulation of surfactant-like material within the alveoli, impairing normal gas exchange. Among its subtypes, the autoimmune form, caused by neutralizing antibodies against granulocyte-macrophage colony-stimulating factor (GM-CSF), is particularly uncommon in children and often mimics atypical infections. We describe the case of a 12-year-old girl with progressive dyspnea, hypoxia, and declining physical performance over four months. Imaging revealed diffuse bilateral ground-glass opacities, and initial treatment for atypical pneumonia showed minimal improvement. Further workup, including bronchoalveolar lavage and lung biopsy, identified alveolar spaces filled with periodic acid-Schiff (PAS)-positive proteinaceous material. Serologic testing confirmed elevated GM-CSF autoantibodies, establishing the diagnosis of autoimmune PAP. The patient required supplemental oxygen and underwent multiple whole lung lavages (WLL), ultimately achieving significant clinical improvement and functional recovery. This case underscores the importance of considering autoimmune PAP in pediatric patients with unexplained interstitial lung disease unresponsive to conventional therapy. Early testing for GM-CSF autoantibodies and timely initiation of WLL may prevent misdiagnosis and lead to favorable outcomes.