Confirming the Diagnosis of Amyloidosis

Amyloidosis is a general term for diseases characterised by the deposition of insoluble amyloid fibrils in organs or tissues, leading to organ dysfunction and, in many cases, death. Amyloid fibrils are derived from soluble precursor proteins, with the number of known amyloidogenic proteins increasing over time. The identity of the precursor protein often predicts the disease phenotype, although many of the amyloidoses have overlapping clinical features. Most patients with amyloidosis will require biopsy of an involved organ or tissue to confirm the diagnosis. Cardiac transthyretin amyloidosis, however, may be diagnosed without a biopsy provided stringent criteria are met. Where amyloid is confirmed histologically, the identity of the amyloidogenic protein must be determined, given several of the amyloidoses have disease-specific therapies. Laser capture microdissection and tandem mass spectrometry, LCM-MS, has revolutionised amyloid subtyping, being able to identify the amyloidogenic protein more reliably than antibody-based methods such as immunohistochemistry. Here we summarise the biopsy approach to amyloidosis, as well as the non-biopsy diagnosis of cardiac transthyretin amyloidosis. Proteomic and antibody-based methods for amyloid subtyping are reviewed. Finally, an algorithm for confirming the diagnosis of amyloidosis is presented.