discussion
Amyloidosis can be classified into systemic and localized, and can be
classified according to the type of deposited fibrinogen into
immunoglobulin light chain amyloidosis (AL), amyloid A amyloidosis (AA),
β2 microglobulin amyloidosis (Aβ2M) and transthyretin amyloidosis
(ATTR).(3) In systemic amyloidosis, the amyloid is
deposited away from the site where it is produced, and it is transported
via the circulatory system to the site of deposition. In localized
amyloidosis, the location of amyloid production and deposition are the
same. It is mainly caused by the AL amyloid, which is produced and
deposited in local sites.(4) The exact etiology of
localized amyloidosis is not yet known.
When amyloidosis is suspected, it requires tissue biopsy under local
anesthesia and microscopic examination (using H&E and Congo red stains)
are usually sufficient to establish a diagnosis. The next step is to
exclude other organ involvements in systemic amyloidosis, then exclude
underlying systemic disease (e.g. chronic inflammatory arthritis,
tuberculosis, familial Mediterranean fever, Crohn’s disease…etc).
Finally, it’s important to establish the subtype of amyloidosis; This is
usually tested using serum or urine immunofixation electrophoresis to
search for a clonal disorder.(5)