[Pulmonary amyloidosis and non-amyloid immunoglobulin deposits]

The amyloidoses are characterised histopathologically by the tissue deposition of fibrillar amyloid, specifically stained by Congo red and birefringent under polarised light. This characteristic is linked to a beta-folded structural configuration that is the common denominator of the amyloidoses which may have more than twenty distinct protein precursors. The most common is AL amyloidosis which is of immunoglobulin origin. It may be organ limited, or systemic (with predominant cardiac involvement). Limited bronchopulmonary amyloidosis, usually AL, may manifest itself as either tracheobronchial deposits or parenchymal nodules or masses. Diffuse interstitial pulmonary amyloidosis with clinical manifestations is rare and usually associated with systemic AL amyloidosis and deposits involving the alveolar-capillary gas exchange zone. Amyloidosis may also manifest itself as pulmonary hypertension, amyloid hilar and mediastinal adenopathy or pleural involvement. AL amyloidosis may be associated locally with pulmonary lymphoma. Occasionally, non-fibrillar, Congo red-negative, immunoglobulin deposits may occur, presenting as parenchymal pulmonary nodules or cysts. Exceptionally immunoglobulin deposits may show a cellular or extra-cellular crystalline structure.