A practical approach to the diagnosis of systemic amyloidoses

Abstract

Key Points• The first wide, prospective report on the role of IEM in the differential diagnosis of systemic amyloidosis.• IEM allows for the correct characterization of the amyloid protein in virtually all cases and represents a viable alternative to mass spectrometry.Accurate diagnosis of systemic amyloidosis is necessary both for assessing the prognosis and for delineating the appropriate treatment. It is based on histologic evidence of amyloid deposits and characterization of the amyloidogenic protein. We prospectively evaluated the diagnostic performance of immunoelectron microscopy (IEM) of abdominal fat aspirates from 745 consecutive patients with suspected systemic amyloidoses. All cases were extensively investigated with clinical and laboratory data, with a follow-up of at least 18 months. The 423 (56.8%) cases with confirmed systemic forms were used to estimate the diagnostic performance of IEM. Compared with Congo-red-based light microscopy, IEM was equally sensitive (75% to 80%) but significantly more specific (100% vs 80%; P < .001). In amyloid light-chain (AL) amyloidosis, k cases were more difficult to diagnose (sensitivity 71%), whereas the analysis of abdominal aspirate was informative in only 40% of patients with transthyretin amyloidosis. We found a high prevalence (20%) of a monoclonal component in patients with non-AL amyloidosis, highlighting the risk of misdiagnosis and the need for unequivocal amyloid typing. Notably, IEM identified correctly the specific form of amyloidosis in >99% of the cases. IEM of abdominal fat aspirates is an effective tool in the routine diagnosis of systemic amyloidoses. (Blood. 2015;125(14):2239-2244) IntroductionAmyloidosis is a heterogeneous group of diseases that share the deposition of amyloid fibrils in organs and tissues, with the same characteristic cross-b-sheet secondary structure, independently of their protein primary structure.1 More than 30 unrelated autologous proteins can produce systemic amyloidoses, 2-5 either localized or systemic. The various forms differ in pathogenesis and prognosis, but they usually show overlapping clinical manifestations, making their differentiation on clinical grounds very difficult. Precise amyloid typing is crucial for the adequate treatment of patients because the various forms require different approaches, which can range from autologous stem cell transplantation in amyloid light-chain (AL) amyloidosis to liver transplantation in transthyretin (TTR) amyloidosis (ATTR). 2,4,5 Diagnosis and classification are based on histologic demonstration of amyloid deposits and characterization of the amyloid precursor. Abdominal subcutaneous fat aspiration with a fine needle is fast and harmless and is the most common diagnostic tool when a systemic form is suspected, 6 offering a convenient alternative to organ biopsy. The resulting tissue smear is examined by polarized light microscopy (LM) after Congo red staining in order to detect the presence of amyloid. The second step is to identify the amyloidogenic protein in order to u...

The lung in amyloidosis

“…The diagnosis of amyloidosis should be based on tissue biopsy. Sampling of easily accessible sites, such as abdominal fat [6] or minor salivary glands [7] can spare organ biopsy in most patients. An increased risk of haemorrhage has been reported with organ biopsy, with <5% bleeding complications in liver biopsies [8] where the transjugular approach should be preferred.…”

“…Since the clinical characteristics of the different forms of amyloidosis are similar, but treatment differs radically, targeting different precursors and pathogenic mechanisms, the unequivocal identification of the amyloid type is vital to avoid therapeutic errors. Typing of the amyloid deposits can be performed using immunohistochemistry in specialised laboratories [13], immune-electronmicroscopy [6] and mass spectrometry [14,15].…”

What is new in diagnosis and management of light chain amyloidosis?

“…The diagnosis requires the demonstration of amyloid deposits in a tissue biopsy. With an 81% diagnostic sensitivity in AL amyloidosis, 13 abdominal fat is the most easily accessible biopsy site and can be innocuously aspirated. In case of a strong clinical suspicion, biopsies should be obtained at additional sites in patients with negative fat aspirate.…”

“…This technique can achieve 100% specificity and can correctly classify more than 99% of patients with systemic amyloidosis. 13 Being not antibody-dependent, mass spectrometry-based proteomics can overcome the limitations of light microscopy immunohistochemistry, greatly improving the diagnostic accuracy. 18 Mass spectrometry diagnostics can be performed after laser capture microdissection of Congo red-positive areas from slides obtained from paraffinembedded tissue 19 or on protein extracted from the whole sample.…”

New and developing therapies for AL amyloidosis

“…Fibril typing is then critical to determine appropriate therapy and is most widely performed through immunohistochemistry, which produces definitive results in about two-thirds of patients of AL amyloidosis [7]. Additional approaches include immuno-electron microscopy [8] and mass spectrometry, which can identify the amyloid protein in up to 98% of cases [9]. Detailed characterization of the underlying clonal hematological disorder is a further crucial step in planning the optimal treatment strategy.…”