This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Interstitial Lung Disease, Subject name: Medicine
Periodic Acid Schiff (PAS) stain positive intra-alveolar material is seen in? 
Select and explain. 
A. Alpha 1 antitrypsin deficiency, B. Pulmonary Alveolar Proteinosis, C. Abetalipoproteinemia, D. Lipoid pneumonia
B: Pulmonary Alveolar Proteinosis
Answer: B: Pulmonary Alveolar Proteinosis 
Explanation: PAS material in alveoli is accumulated surfactant due to decreased turnover in pulmonary alveolar proteinosis. Characterized by dysfunction of alveolar macrophages which results in decreased surfactant clearance The same material may be coughed up by patients and described as chunky gelatinous plugs. Lipoid pneumonia will show fat globules in macrophages.