Pulmonary alveolar proteinosis postlung transplantation: A causation conundrum

Pulmonary alveolar proteinosis (PAP) is a rare pulmonary disorder caused by defective granulocyte-macrophage colony-stimulating factor signaling, leading to abnormalities of macrophage metabolic and immune functions, with resultant impaired surfactant metabolism and its accumulation within the alveoli. PAP can relapse in patients who underwent lung transplantation for PAP related to genetic defects. However, its occurrence is exceedingly rare in lung allografts of patients who underwent lung transplantation for other primary end-stage lung disease. Prompt diagnosis and appropriate treatment strategy are crucial to prevent the decline in the allograft function and to avoid unnecessary empiric treatments for rejection and/ infection. Here we present a case of PAP in a patient, 8 months postbilateral lung transplantation for COVID-19 fibrosis.