Pulmonary Alveolar Proteinosis (PAP) vs Idiopathic Pulmonary Fibrosis (IPF) - Diagnostic Considerations
PAP is a rare clinical syndrome that is characterized by the accumulation of surfactant in the pulmonary airspaces (Greenhill SR and Kotton DN, 2009). Lung biopsies usually reveal presence of diastase-resistant intra-alveolar exudate with minimal interstitial fibrosis and "honeycombing". In some patients with PAP, however, interstitial fibrosis can be considerable and at least two PAP patients were initially thought to have IPF (Arbiser ZK et al., 2003). PAP is no longer idiopathic, since functional deficiency of granulocyte-macrophage colony-stimulating factor (GM-CSF) appears to cause the disease. The presence of autoantibodies against GM-CSF in serum is considered to be diagnostic for PAP (Kitamura T et al., 1999; Bonfield, TL et al., 2002). It is highly important to excude PAP as a possible diagnosis since the prognosis of PAP and IPF are different. The life expectancy of PAP patients is longer, 5-year mortality is 20% vs 80% for IPF patients. Also, patients with PAP favorably respond to pulmonary lavage and can possibly be treated with GM-CSF. It is unfortunate that GM-CSF antibodies test is not yet widely available in clinical laboratories.
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