What is systemic AA amyloidosis?
Systemic AA amyloidosis, formerly called secondary or reactive amyloidosis, is attributable to deposition of fragments of SAA that forms amyloid fibrils. It can complicate any chronic inflammatory disorder, whether infectious, neoplastic, rheumatic, or heritable periodic fever syndromes. Notably, up to 7% of patients with AA amyloidosis have no clinically obvious chronic inflammatory disease. Some of these may have an undiagnosed autoinflammatory syndrome (see Chapter 79 : Familial Autoinflammatory Syndromes) or Castleman disease. The clinical feature most common in AA amyloidosis is renal involvement (70%–90%) followed by hepatosplenomegaly. Clinical cardiac disease and autonomic nerve involvement are less common than in AL amyloidosis. Patients with AA amyloidosis attributable to a chronic inflammatory (rheumatic, Crohn’s) disease have a slow progression, whereas AA amyloid attributable to an untreated chronic infection can be rapidly progressive.
