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INTRODUCTION

Deposits of endogenous body constituents or exogenous materials in amounts sufficient to deform structure and impair function can occur virtually anywhere in the body. Deposits of endogenous materials in the lungs or airways cause a variety of diseases (Table 63-1). These may have different clinical manifestations depending on location (i.e., pulmonary parenchyma or conducting airways). This chapter deals with two of these manifestations: amyloidosis and diffuse pulmonary calcification and its variants. Others depositional diseases are discussed elsewhere in this text.

TABLE 63-1Depositional Diseases of the Lungs

AMYLOIDOSIS

Amyloidosis refers to the extracellular deposition of amyloid, a fibrillar, proteinaceous, insoluble material that has characteristic light, ultrastructural, and histochemical features1,2 (Fig. 63-1). Electron microscopic examination of amyloid reveals a dominant (95%) fibrillar component with distinctive periodicity, associated with a lesser (5%) pentagonal doughnut-shaped glycoprotein component, physically and chemically identical in all forms of amyloid, which is derived from a soluble plasma protein, soluble amyloid P protein (SAP). Amyloid also includes various glycosaminoglycans, for example, heparan sulfate and certain apolipoproteins (E and J).3 Radiographic diffraction studies of amyloid show the fibrils to be arrayed in a β-pleated sheet configuration. This accounts for the ordered binding of the histochemical stain Congo red such that Congo red–stained amyloid appears apple-green under polarized light. When amyloid is deposited in tissues it may produce a wide variety of clinical manifestations mediated by atrophy of parenchymal cells (e.g., glomeruli), interference with mechanical function (e.g., heart and lungs), or impaired vasoconstriction of blood vessels, leading to hemorrhage (e.g., lungs and gastrointestinal tract). Mechanisms of tissue injury include direct tissue toxicity and activation of the unfolded protein response.4 Deposition may occur in multiple organs as a systemic disease or may be limited to a single organ. As a result, classification includes both the specific moiety involved and the clinical syndrome.

Figure 63-1

Amyloid deposition. A. Amyloidoma. Cut surface of lung with white arrows indicating a dense, wax-like lesion that is characteristic of nodular amyloid. Incidental finding at autopsy. B. The typical amorphous appearance of amyloid is seen deposited within the wall of a pulmonary venule. Green birefringence on polarized light examination after staining with Congo red will confirm the amyloid nature of the deposit (H&E ×700). C. Amorphous amyloid in the alveolar interstitial space. Arrow indicates a thickened alveolar septum (H&E ×420). (A. Reproduced with permission from Leslie A. Litzky, MD, Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, Philadelphia.)

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