A40-50 Radiopathological Discordance in an Atypical Case of Pulmonary Alveolar Proteinosis

Abstract Pulmonary Alveolar Proteinosis (PAP) is rare lung condition characterized by alveolar filling with macrophages due to abnormal accumulation of surfactant in the alveolar space. Classical radiologic findings include ground-glass opacities and interlobular septal thickening. This is a case of a 44-year old gentleman with a 30-pack year smoking history who presented to his local hospital with persistent cough and worsening shortness of breath. He had pulmonary tuberculosis in 2022 but otherwise had an unremarkable medical history. He previously worked as a stone mason for 19 years. CT imaging revealed ground glass opacities and diffuse cysts and he was initially managed as a case of smoking-related ILD with oral and intravenous steroids. A bronchioalveolar (BAL) fluid culture had heavy growth of S pneumoniae and K oxytoca and he was commenced on IV antibiotics and antifungals on suspicion of an atypical chest infection. Autoimmune screen was negative. The patient however continued to deteriorate and was put on high flow nasal oxygen due to increasing oxygen requirements; in parallel, a repeat CT scan showed worsening ground glass change and cystic disease. The patient was referred to our institution and discussed in our ILD multidisciplinary team meeting. A serial review of his scans showed progressive changes suspicious for mucinous adenocarcinoma. A CT-guided biopsy was done and histology showed alveolar spaces filled with granular material which stained strongly for periodic acid-Schiff (PAS). The patient underwent a whole lung lavage with subsequent clinical improvement. Supplemental oxygen requirement decreased to 2 liters/min. Serological testing for Granulocyte-Macrophage Colony Stimulation Factor (GM-CSF) autoantibodies was done and later returned positive. A genetic screen was also done due to the unusual radiological presentation. The patient was discharged on ambulatory oxygen with a clinic follow up for definitive treatment with inhaled GM-CSF. The presence of diffuse ground-glass opacities without the classic crazy-paving pattern, accompanied by cystic changes in histologically-confirmed pulmonary alveolar proteinosis (PAP), is exceedingly rare in literature. This finding emphasizes the need to consider PAP in the differential diagnosis, even when imaging features overlap with other conditions. Anti-GM-CSF antibodies demonstrate 100% sensitivity and specificity for autoimmune PAP in the appropriate clinical context. Although biopsy is typically unnecessary in classic PAP cases, this should be considered when the diagnosis is uncertain. Furthermore, the patient’s marked improvement following therapeutic whole-lung lavage highlights the effectiveness of this treatment, even in atypical presentations of the disease. This abstract is funded by: None