[A case of pulmonary alveolar proteinosis presenting with miniscule ground-glass opacity in the apex of the left lung].

A 66-year-old man was found to have a very small ground-glass opacity in the apex of the left lung. Because the ground-glass opacity had slightly enlarged after 2 years, video-assisted thoracic surgery (VATS) biopsy was performed. The histological findings showed the alveolar spaces to be filled with PAS-positive granular materials, so pulmonary alveolar proteinosis was diagnosed. Although his bronchoalveolar lavage fluid (BALF) did not have a milky appearance, his serum and BALF GM-CSF autoantibody and serum KL-6 levels were elevated. Asymptomatic pulmonary alveolar proteinosis may appear as very small ground-grass opacities.