What is pulmonary alveolar proteinosis (PAP)?

PAP is a lung condition that is caused by a build-up of proteins, fats and other substances (collectively called surfactant) in the air sacs of the lungs, called the alveoli. The alveoli are the part of the lungs that contain air. It is there that gases between the lungs and the blood are exchanged.

PAP is a rare disease, affecting about 1 person in 100,000 people worldwide, with fewer than 10,000 of them in the U.S. It generally develops in adults, but it can be congenital (something you are born with). It is sometimes called phospholipidosis or pulmonary alveolar lipoproteinosis.

Are there different types of pulmonary alveolar proteinosis (PAP)?

Yes. Types include:

  • Autoimmune pulmonary alveolar proteinosis (aPAP): This type is the most common and is believed to represent about 90% of adults who get it. These adults are mostly between the ages of 30 and 60 years old.
  • Secondary PAP: This type is a result of having another type of disease or condition or of being exposed to a toxin of some type.
  • Congenital: There is a form of PAP that happens because of genetic defects passed down in families.

Who gets pulmonary alveolar proteinosis (PAP)?

This condition happens more often in men than in women. It usually affects people between the ages of 30 and 60. Exposures like dusts and smoking increase the risk of PAP, which may explain why it has been recognized more often in men.

What causes pulmonary alveolar proteinosis (PAP)?

In the majority of PAP cases in adults, the cause is suspected to be a lack of or a problem with granulocyte-macrophage colony-stimulating factor (GM-CSF). This substance is needed to make certain immune cells develop. Without it, the air sacs are not able to clear out all traces of protein-containing materials. This leads to accumulation of debris in the air sacs and eventually to breathing problems.

What are the symptoms of pulmonary alveolar proteinosis (PAP)?

PAP has the following symptoms:

  • Shortness of breath, also called dyspnea
  • Chest pain or tightness
  • Fever
  • Weight loss
  • Cough (sometimes, but not always)
  • Low levels of oxygen in the blood
  • Nail clubbing (abnormal growth of toenails or fingernails)

Last reviewed by a Cleveland Clinic medical professional on 06/06/2018.


  • Expert knowledge and experience of healthcare providers at Cleveland Clinic
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