Pulmonary alveolar proteinosis (PAP) should be suspected when the classic imaging finding of a “crazy paving” pattern is seen on chest CT; however, this appearance can be subtle and PAP may present with a range of varying CT features. The diagnosis is confirmed by identifying eosinophilic extracellular material that stains positively with Periodic Acid–Schiff on bronchoalveolar lavage specimens. The autoimmune form of PAP (aPAP) is confirmed by detecting anti–GM-CSF antibodies in the patient’s serum. We propose a novel classification with definite, probable and possible aPAP diagnosis based on various combination of chest CT, BAL and anti-GM-CSF antibodies.

Historically, whole-lung lavage has been the first-line treatment and should be performed only in expert centres. Following positive results from recent randomised, placebo-controlled trials, inhaled GM-CSF supplementation with molgramostim or sargramostim is now equally positioned as first line therapy, WLL remaining the preferred option for patients with respiratory failure, particularly at the time of diagnosis.

Rituximab and plasmapheresis may be prescribed as third- and fourth-line treatments, respectively, and lung transplantation may be considered for eligible patients with end-stage respiratory failure. A deeper understanding of aPAP pathogenesis has opened new therapeutic avenues, including the use of PPARγ agonists or statins; however, future research must define the optimal long-term treatment strategy and, crucially, establish clear evidence-based criteria for when therapy should be commenced.