Features of pulmonary alveolar proteinosis on BAL:
(1) The collected lavage fluid is milky and opaque rather than clear.
(2) Smears show granular, amorphous extracellular material (globules). On Papanicolaou staining these globules stain either green, orange, or green rim around an orange center.
(3) Most patients with PAP have > 100 globules per slide smear. The maximum number seen in a non-PAP case (polymyositis) was 17; most non-PAP lavage fluids show <= 3 per slide.
(4) The globules are (a) PAS positive and diastase resistant and (b) Alcian blue negative.
(5) The lavage fluid shows a low cellularity.
where:
• Alcian blue is a stain for polysaccharides.
Electron microscopy can be used to demonstrate lamellar bodies for confirmation of suspected cases.
Limitations:
• The nature of the cytologic preparation is not described. I assume based on the gross appearance that the smears were direct without concentration. The number of globules is quantitated per slide and not per volume of lavage fluid.
• I am not sure how PAP would appear on a Thin Prep since this might filter out some of the globules.
• The globules are large enough that they could be counted in a hemocytometer chamber. Since a known amount of lavage fluid was used (3 aliquots of 50 mL sterile normal saline) a semiquantitative count should be possible, which would reduce variability.
