Pulmonary Pathology Online
Pathology of Pulmonary Alveolar Proteinosis
Pulmonary alveolar proteinosis is a rare condition and patients with this disease usually present with insidious dyspnoea that has progressed over months, sometimes with mild systemic symptoms such as low grade fever and weight loss.
Usually, it has a benign course with eventual resolution.
Rarely, rapid progression to respiratory failure is seen.
Death occurs due to progressive filling of alveoli or superimposed infection.
Clinical signs are few, and minor in comparison to the radiological opacification which commences as bilateral peri-hilar feathery and nodular shadowing.
Computarised tomography may show a 'mosaic' of involved and spared lobules.
The disease is characterized histologically by eosinophilic material filling the alveoli.
The material has a dense, finely granular appearance and is PAS-positive and diastase resistant.
There is relative preservation of the parenchymal architecture and no inflammatory response.
Cholesterol crystal clefts and foamy macrophages are present, the latter frequently degenerating.
Interstitial changes are initially minimal, although type-II pneumocyte hyperplasia may be present.
Pulmonary alveolar proteinosis may be heralded by a phase of endogenous lipid pneumonia ( indicated by the foamy macrophages ).
The differential diagnosis includes pneumocystis pneumonia and protein-rich edema.
The former is foamy with tiny haematoxyphil dots, the latter much more homogenous.
Both lack of granularity, acinar clefts, foamy macrophages and strong PAS positivity of alveolar proteinosis.
In case of doubt, immunohistochemistry (for pneumocystis and for surfactant apoprotein), a Gomori-Grocott stain (for pneumocystis) or electron microscopy may assist.
Electron microscopy demonstrates that the granular material is composed of large numbers of osmiophilic lamellar bodies up to 5 microns in diameter.
It resembles surfactant and stains for surfactant apoprotein.
This disease is often idiopathic. It may occurs after exposure to irritating dusts, chemicals and in immunosuppressed individuals.
Pulmonary alveolar proteinosis may be associated with dusty occupations (particularly acute high dose silica exposure) and immunosuppression (leukemia, lymphomas, their treatment and related opportunistic infections).
Animal models employing heavy dust exposure implicate overproduction of surfactant, compounded by inadequate clearance.
Cases associated with immunosuppression stain poorly for surfactant and here the material may represent cell debris.
In children the disease may reflect compensatory oversecretion in the face of surfactant apoprotein B deficiency.
The alveolar material promotes the growth in vitro of organisms such as Nocardia asteroides and secondary nocardiosis is a recognized complication.
Treatment is by high volume alveolar lavage.
Summary of findings:
Histologically, it is characterized by accumulation of dense, amorphous, PAS-positive, lipid-laden material in intra-alveolar spaces and clinically by respiratory difficulty, cough, fever and yellow sputum, containing gelatinous material.
Intra-alveolar exudates consist of surfactant-like material, necrotic alveolar macrophages and granular pneumocytes. Alveolar walls show little inflammation.
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