Amyloidosis may involve any site in the upper or lower respiratory tract, the larynx being the most common site. It may also affect the esophagus and mediastinal nodes, or produce mass lesions in the neck. Tracheal involvement may occur as part of a generalized amyloidosis, whether primary or secondary, or in a localized form, which itself can be primary or secondary to plasmacytoma.

Biology. The primary localized form affects adults, and only exceptional cases are reported in children.15 The other forms follow the age distribution of generalized amyloidosis and solitary tracheal plasmacytomas. Tracheal obstruction may occur in severe forms and the obstruction may lead to infections and respiratory failure. Bleeding, although not frequent, may be massive and even fatal, as occurred in a patient with laryngeal amyloidosis.16 The bleeding problem is probably related to blood vessels, which themselves may have amyloid in their walls and may not constrict normally.

Pathology. Gross appearance, as seen on bronchoscopy, varies from diffusely heaped up edematous mucosa to single or multiple nodules protruding into the lumen. Macroscopically, tracheal amyloidosis has a firm grey, waxy cut surface (Figure 3-59 [Color Plate 8]).

Microscopically, nodules of amorphous, lightly eosinophilic material are deposited in the mucosa (Figure 3-60 [Color Plate 8]) and large deposits may erode into cartilage. Scant chronic inflammation and fibrosis may be present. Vascular amyloidosis may be noted. Where amyloid extends deeply, it may involve the mucosal glands, producing globules of eosinophilic material replacing the atrophic gland acini. Cartilaginous change, calcification, and osseous metaplasia may occur. Foreign body giant cells and granulomas often surround the amyloid. In localized tracheal amyloidosis secondary to solitary plasmacytoma, amyloid material usually comprises a minority of the tumoral tissue, but it may be even more extensive than the neoplastic plasma cells.

Histochemical staining with Congo red shows apple-green birefringence under polarized light, which confirms the diagnosis (Figure 3-61 [Color Plate 8]). Other stains such as methyl violet or thioflavin-T may also be used. Electron microscopy shows the typical fibrillar structure of amyloid. Immunoglobulin light chains were present and mixed with amyloid in one case. Bronchoscopic differential diagnoses include tra-cheopathia osteoplastica, relapsing polychondritis, inflammatory lesions, and tumors.

With regard to histology, amyloid deposits may be replaced with cartilage and bone. It must be distinguished from other lesions with cartilage and bone, particularly tracheopathia osteoplastica, but also from degenerative and reparative changes that can occur with tracheomalacia. Foreign body reaction to the amyloid should not be mistaken for granulomatous diseases like tuberculosis and sarcoidosis.

Prognosis is generally good in primary localized forms, but the risk of bleeding exists. Laser treatment or surgical excision may be necessary in obstructive lesions. Nodular tracheal amyloidosis may cause obstruction, and postobstructive infection may develop. In diffuse tracheobronchial amyloidosis, post-obstructive infection and respiratory failure may occur. In generalized amyloidosis, pulmonary involvement with pulmonary hypertension, cardiac involvement with arrhythmias and failure, or other complications may complicate the clinical course.

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