[Amyloidosis and amyloid deposits. Amyloidosis of the lower respiratory tract].

Amyloid is defined by its affinity for Congo red, which gives it a characteristic green birefringence in polarised light. This peculiarity is the result of its structure in beta-fibrillary folds, which is common to all biochemical varieties of amyloidosis whatever the origins of the immunoglobulin, reactive AA or prealbumin for example. Tracheobronchial amyloidosis exists in two forms: a pseudotumoral mass of a few millimeters in diameter discovered by chance at endoscopy without producing any clinical signs; and multi-focal sub-mucosal plaques which lead to bronchial stenosis and which can be destroyed by laser. Parenchymal amyloid can be nodular, or diffuse and interstitial. The amyloid nodules are single or multiple and their size varies from a few millimeters to several centimeters; they lead to few symptoms and do not require any treatment in the majority of cases if the diagnosis has been achieved by transparietal puncture for example (but the diagnosis is made above all by the excision of a mass which is presumed to be neoplastic). Diffuse interstitial parenchymal amyloid involves the alveolar region: it is a not uncommon finding at necropsy when it only infiltrates the vessels, it can give rise to the symptomatology of an interstitial pneumonia when there is widespread infiltration of the alveolar-capillary zone. The distinction between this type of diffuse interstitial amyloid and the miliary micro-nodular amyloidosis is sometimes difficult with overlapping between these two entities. Amyloid may also involve the pleura, the mediastinal nodes, the respiratory muscles and in particular the diaphragm; macroglossia may be responsible for obstructive sleep apnoea. Tracheobronchial amyloid and pulmonary nodules are generally localised to the respiratory system, whereas diffuse interstitial amyloid is combined in a group along with systemic amyloid. There is no specific treatment for amyloidosis.