Unraveling Pulmonary Alveolar Proteinosis

  • Talita Utomo BSc Biomedical Science, University of Sheffield
  • Jialu Li Master of Science in Language Sciences (Neuroscience) UCL


Pulmonary Alveolar Proteinosis (PAP) stands as a rare anomaly in the world of respiratory disorders. This disease only affects 0.37 per 100,000 people.1 This article will examine PAP thoroughly, focusing on insights to foster a clear understanding of this condition. Within the lung's intricate architecture, PAP disrupts the normal function of alveoli, the primary site for oxygen exchange. This disruption results from an accumulation of proteins in the alveoli, posing challenges to efficient respiratory processes.

Throughout this article, we'll delve into essential aspects such as causes, risk factors, and prevalent symptoms associated with PAP. Diagnostic procedures, including imaging studies, pulmonary function tests, and biopsies, will be outlined to provide a comprehensive understanding of the diagnostic landscape.

The article will also further address available treatment options, ranging from Whole Lung Lavage procedures to supportive therapies like oxygen supplementation. A focus on the long-term management of PAP, its impact on daily life, and available resources for individuals navigating this condition will also be covered. Lastly, we'll touch on current research and potential future developments, offering readers a glimpse into ongoing studies and clinical trials that may shape the direction of PAP management.

Understanding the basics of the lungs

As a vital component of the respiratory system, the lungs are intricate organs that exchange carbon dioxide and oxygen to maintain life. They are situated in the thoracic cavity and are protected by the rib cage. There are lobes in each lung; the left lung has two lobes and the right lung has three. The tubular trachea divides into bronchi, which are smaller airways, and alveoli, which are tiny air sacs.2

The small engines that facilitate the exchange of gases necessary for life are called alveoli, which resemble small grapes. These air sacs, encircled by a complex web of capillaries, offer a large surface area for effective gas exchange. Breathed airborne oxygen diffuses past the delicate alveolar walls and into the circulation, where it binds to red blood cell haemoglobin. At the same time as a waste product of cellular metabolism, carbon dioxide diffuses into the alveoli from the blood, where it awaits to expire.3

The carefully designed breathing mechanism is upset by Pulmonary Alveolar Proteinosis (PAP). Surfactant, a complex combination of lipids and proteins essential for preserving alveolar integrity and lowering surface tension, accumulates abnormally within the alveoli in PAP. The once-efficient air exchange passages get clogged with protein as a result of this buildup. The alveoli consequently find it difficult to carry out their gas exchange functions. A series of symptoms, including coughs, dyspnea (shortness of breath), and chest pain, are brought on by this disease. The reduced ability to exchange gases can lead to hypoxemia, a disorder marked by low blood oxygen levels, which exacerbates the respiratory difficulties that people with PAP have. This change in the alveoli's typical function highlights how important it is to fully understand how PAP affects the lungs and what it means for respiratory health in general.4,5

Causes and risk factors

Pulmonary alveolar proteinosis (PAP) may be divided into two groups: primary (idiopathic) PAP and secondary PAP. 90% of PAP cases have been noted to be primary PAP.6

A key factor in primary PAP is hereditary susceptibility. People who have a family history of PAP are more likely to have it, which points to a genetic component that scientists are now looking into. The details of the genetic factors are still unknown and represent an important area of research.1 Moreover, the development of primary PAP is significantly influenced by autoimmune variables. Here, the body's own tissues are mistakenly targeted by the immune system, which causes an abnormal build-up of proteins in the alveoli, which are small air sacs that regulate gas exchange. The exact processes that set off this autoimmune reaction are being studied, highlighting the complex connection between immunological imbalance and PAP symptoms.5

However, secondary PAP is associated with exposure to the environment. The chain of events leading to PAP can be started by smoking cigarettes, vaping, infections, inhaling dust and chemicals, exposure to toxic fumes, or other environmental factors. This kind of illness is frequently linked to particular work-related risks. There is a higher risk of contracting PAP associated with industries including mining, metallurgy, and agriculture, where workers are continuously exposed to particulate matter.5,7 


Medical professionals use a range of diagnostic techniques to diagnose PAP:

Imaging studies (X-rays, CT Scans) 

Generally speaking, chest X-rays and computed tomography (CT) scans are the first steps in the diagnostic process. These methods of imaging are essential for identifying distinctive patterns linked to PAP. One unique aspect that these scans might reveal is the "crazy paving" look, when the lung parenchyma resembles unevenly shaped paving stones. X-rays and CT scans provide a thorough picture of the scope and severity of the illness in addition to verifying the existence of anomalies, which paves the way for additional diagnostic procedures.8

Pulmonary function tests (PFTs)

PFTs, or pulmonary function tests, are essential for determining the lungs' functional capability. These tests are essential for determining any respiratory function deficits. On PFTs, patients with PAP frequently show patterns of restrictive lung disease, which suggests impaired lung expansion. Metrics like lung volumes, capacities, and flow rates give medical professionals important information to assess how PAP affects respiratory function and help create individualized treatment plans.9

Bronchoalveolar lavage (BAL)

This diagnostic technique includes using a saline solution to wash the alveoli and airways of the lung. Following this, the fluid recovered from the lavage is examined to determine its cellular and biochemical makeup. When it comes to PAP, BAL is very helpful. A characteristic of the illness, milky, proteinaceous material, may be seen in the lavage fluid. This identification offers concrete proof of the abnormal material present in the pulmonary environment, which greatly aids in the verification of the PAP diagnosis.1

Biopsy for confirmation

Although BAL, pulmonary function testing, and imaging tests provide an array of diagnostic data, a lung biopsy is frequently necessary for a conclusive diagnosis. This is an invasive treatment that involves taking a small sample of lung tissue for microscopic analysis. By providing specific insights into the changes in cells inside the alveoli, the biopsy helps to distinguish PAP from other lung disorders. Even though the biopsy is crucial for a precise diagnosis, it is usually saved for situations in which other diagnostic techniques have failed to produce a definitive outcome.1

Treatment options

There are two vital treatments for PAP: Whole Lung Lavage, a procedure targeting the removal of accumulated proteins, and supportive therapies, including oxygen supplementation and symptomatic relief medications. 

The main treatment approach for patients with pulmonary alveolar proteinosis is whole lung lavage (WLL). In order to get rid of the accumulated proteinaceous debris in the alveoli, this method entails carefully cleaning the lungs. To ensure comfort during WLL, the patient is usually put under general anaesthesia. One lung at a time is lavaged, drawing out the troublesome material with an infusion of warmed saline solution and subsequent draining. Until the lavage fluid becomes clear, a sign that the aberrant material has been successfully removed, the procedure is carefully repeated. Respiratory discomfort during the operation, infections, and the requirement for further sessions to maintain effectiveness are possible risks but the benefits of this operation greatly outweigh the risks.5,10

In cases of hereditary PAP, Whole Lung Lavage is less practical, especially in pediatric patients. Potential treatments include gene therapy, which requires preclinical studies before being tested on patients. A novel approach being explored is targeting lipid (fat) homeostasis, particularly cholesterol. Statin therapy, known for reducing cholesterol levels, has shown promise in improving PAP, providing a potential alternative for future therapeutic development.11


The uncommon lung condition known as pulmonary alveolar proteinosis (PAP) is typified by an excessive build-up of proteins in the alveoli, which are tiny air sacs vital to oxygen exchange. There are two types of PAP: primary and secondary. 

Imaging tests such as CT and X-ray scans, pulmonary function tests, bronchoalveolar lavage (BAL), and, if required, a lung biopsy are all part of the diagnostic procedure. Whole Lung Lavage (WLL), a process that gets rid of the lungs of deposited proteins, is the usual treatment PAP patients undergo. Some novel treatments are being researched such as statin therapy. 

Even with research advancements, PAP management is still difficult, necessitating a thorough knowledge of environmental, autoimmune, and genetic variables in order to develop efficient treatment plans. Continual research initiatives aim to improve these methods thus improving the prognosis for patients suffering from this uncommon lung disease.


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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Talita Utomo

BSc Biomedical Science, University of Sheffield

Talita is a second-year Biomedical Science student with a passion for science and a commitment to making a meaningful impact. Beyond her professional journey, she has discovered an interest in writing health articles, combining her scientific background with effective communication skills.

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