Background: Pulmonary alveolar proteinosis (PAP) is a rare lung disease that mainly presents with dyspnea. PAP diagnosis can be easily missed in the background of a coronavirus disease 2019 (COVID-19) infection, due to the similarity of their presentation and radiological findings. We present a case report of a post-COVID-19 patient, who later developed severe PAP. Case presentation: A 55-year-old male patient presented to the emergency department with progressive exertional dyspnea and hypoxia following a COVID-19 infection. Chest X-ray showed severe bilateral infiltrates. Patient received multiple courses of broad-spectrum antibiotics and prolonged course of corticosteroids without improvement. "Crazy paving" appearance in a follow up chest computed tomography raised the suspicion of PAP of what was initially thought to be a post-COVID-19 syndrome presentation. A diagnostic segmental bronchioalveolar lavage with a lung biopsy revealed a proteinaceous material filling the alveoli, with a positive periodic acid-Schiff (PAS) stain. Due to severe hypoxia, therapeutic segmental followed by whole lung lavage was performed with significant improvement. Conclusion: Diagnosing PAP is challenging due to the rarity of the disease. An accurate diagnosis of PAP requires a combination of medical history, imaging, and bronchoalveolar lavage staining positive for PAS. Decision whether to treat with a segmental or whole lung lavage is individualized to each patient. Further studies are needed to confirm whether COVID-19 or long-term use of steroids might be contributing to PAP.
