CTICasesPulmonary Alveolar Proteinosis — Anti-GM-CSF Antibody Diagnosis
Imaging findings
CT demonstrates geographic crazy paving pattern with secondary lobules either completely involved by ground-glass opacity with septal thickening or completely spared, creating a striking lobular mosaic. The pattern is bilateral and predominantly lower lobe predominant in distribution. Diagnosis in this case was established by detection of anti-GM-CSF antibodies in BAL fluid rather than by the characteristic milky appearance of lavage fluid or pathologic lavage analysis, as the bronchoscopy and BAL were performed at an outside institution.
Key takeaways
Anti-GM-CSF autoantibodies can be detected in BAL fluid and serve as a highly specific diagnostic marker for autoimmune (primary) PAP, with sensitivity and specificity reported above 95% in some series. This non-invasive diagnostic approach is increasingly utilized when the typical milky BAL appearance or PAS-positive material on cytology is not available. The treatment mechanism of exogenous GM-CSF supplementation (which overcomes the antibody blockade of native GM-CSF) explains why GM-CSF can both cause and treat PAP depending on context.
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