Rare diffuse diseases of the lung. Pulmonary alveolar proteinosis, lymphangioleiomyomatosis, amyloidosis.

Pulmonary alveolar proteinosis (PAP), lymphangioleyomiomatosis (LAM) and amyloidosis are three unrelated diseases of rare occurrence, with characteristic histopathological features. A pattern of alveolar filling with granular pink material accumulation is characteristic of PAP. This material can be recognized in lung biopsies, but also in bronchial lavage fluid. PAP is clinically related to the abnormal clearance of alveolar surfactant, most commonly due to the disruption of the granulocyte macrophage-colony stimulating factor signalling pathway. Whole lung lavage is the treatment of choice. LAM is characterized by cystic lung degeneration and interstitial proliferation of LAM cells, which express both melanocyte and smooth muscle cell markers, has a typical cystic pattern on CT scan, can be associated clinically with abdominal angiomyolipomas and limphangioleiomyomas, and occurs in female patients, either in isolation or as a manifestation of tuberous sclerosis. Sex hormone manipulation is the therapy of choice in this otherwise progressive disease. Diffuse interstitial or perivascular amyloid deposits in the lung can form in the context of systemic amyloidosis, usually associated with myeloma or monoclonal gammopathy, and less often with chronic inflammatory diseases. Nodular amyloid deposits, in contrast, are not associated with systemic lung disease, and present instrumentally as a coin lesion or lung mass. Isolated tracheobronchial amyloidosis is another rare form that is not related to systemic disease. In all conditions, amyloid has a typical waxy, amorphous, slightly eosinophilic stain, stains red with Congo red and presents a characteristic apple-green birefringence under polarized light, which is essential for diagnosis.