The Diagnostic Path of Amyloidosis. When to Think of it and how to Find it

The diagnosis of amyloidosis has been difficult and troublesome until the introduction of periombelical fat tissue aspirate as the method of choice for tissue biopsy. Nowadays the diagnostic path includes three main steps: suspicion of the disease, periombelical fat tissue aspirate or biopsy of the involved organ(s), and identification of the amyloidogenic protein. Several clinical and biohumoral conditions are highly suggestive of the disease, such as MGUS or multiple myeloma for AL, chronic inflammatory diseases for AA, and a family history of cardiac or peripheral neuropathy for the hereditary forms. However, in case of a tissue sample positive for Congo red staining, these conditions are not sufficient to identify the type of amyloid fibrils. Indeed misdiagnosis, especially in the presence of MGUS, is very likely and deserves particular attention. In most cases traditional immunohistochemistry is no longer adequate and there is a need for further investigations such as immunoelectron microscopy (immunogold) or proteomics with laser dissection and mass spectroscopy. Chemotherapy cannot be started until a definite diagnosis of the type of amyloidosis has been made.