Pulmonary alveolar proteinosis is an uncommon medical condition, entailing the congestion of alveoli with material containing lipoprotein complexes, produced by type II alveolar epithelial cells. It can manifest as an autoimmune, hereditary or secondary medical condition.
Pulmonary alveolar proteinosis (PAP) is a rare condition, whose symptoms are specific to pulmonary pathology, but hardly pathognomonic to the particular disease. Clinical manifestations tend to develop over a period of time; a considerable number of patients (circa 30%) do not report any symptoms, even though PAP is diagnosed due to significant radiologic findings in the lungs.
The condition encompasses three distinct clinical categories. Idiopathic PAP usually leads to symptomatology during adulthood and is diagnosed at that time; congenital PAP is diagnosed in neonates while secondary PAP is a complication of an underlying pathology and also develops in adults .
With regard to the symptoms associated with pulmonary alveolar proteinosis, the ones most commonly reported by patients include dyspnea, which is exertional in nature, fatigue and periodic fever, which tends to be low-grade . Patients may experience loss of weight, mostly non-productive cough, pleuritic chest pain and night sweats. Rarely observed symptoms include hemoptysis and cyanosis. Congenital pulmonary alveolar proteinosis leads respiratory distress syndrome and entails tachypnea, grunting during expiration, nasal flaring, cyanosis, subcostal retractions and, in severe cases, apnea or hypothermia . PAP-induced respiratory distress syndrome is refractory to corticosteroids and surfactants. Lastly, secondary PAP may underlie other pathological conditions, such as myelodysplastic syndromes, an HIV infection, thymic alymphoplasia and a variety of other disorders   .
The diagnosis of pulmonary alveolar proteinosis requires a multitude of examinations and procedures, such as a bronchoalveolar lavage (BAL), chest radiograph, a high-resolution computed tomography (HRCT), pulmonary function tests, blood tests and, rarely nowadays, open lung biopsy.
Currently, BAL is the most useful tool which renders the diagnosis possible. A histological analysis of fluid retrieved via BAL will reveal large alveolar macrophages which closely resemble monocytes and an extensive lymphocytic presence   . Approximately 3/4 of the affected patients are diagnosed with the use of BAL, which also illustrates the presence of granular, eosinophilic lipoprotein complexes.
Radiographs and HRCT
Thoracic x-rays are of use but the findings of bilateral alveolar infiltrates do not correspond to clinical symptoms and are not pathognomonic. An HRCT is expected to yield results, such as ground-glass opacifications and "crazy-paving" patterns formed by interlobular septal thickening next to healthy parenchyma . Nevertheless, this particular finding can also be observed in a plethora of other conditions, such as hemorrhage, acute interstitial pneumonia lipoid pneumonia, and other conditions  .
Pulmonary function tests
Its use is supportive, but not diagnostic of PAP. It reveals a restrictive pattern, diminished FVC and a reduced diffusing capacity.
An open lung biopsy is not commonly employed in current practice, due to the success of BAL in diagnosing pulmonary alveolar proteinosis . However, cases with a high suspicion of PAP with a negative BAL may be investigated surgically for purposes of biopsy.
May be carried out to detect elevated serum anti-GM-CSF antibody titers if the nature of PAP is presumed to be idiopathic.