Amyloidosis is often overlooked because its clinical manifestations can mimic those of more-common diseases. It is important to get a precise diagnosis as early as possible for the prevention of further organ damages.
Amyloidosis is a disorder caused by deposition of insoluble abnormal
amyloid. The kidney is a frequent site of
amyloid deposition. The
amyloid fibrils have a characteristic appearance and generate birefringence under polarized light when stained with the
Congo red dye. Classification of
amyloidosis is based on the precursor
protein that forms the
amyloid fibrils and the distribution of
amyloid deposits as either systemic or localized. Involvement of
amyloid fibrils in kidneys mainly occurs as
amyloid light-chain (AL) or
amyloid A (
AA) amyloidosis. The
potassium permanganate method with
Congo red staining was once used widely to discriminate AL and AA
amyloidoses, but this method has a problem of false positive results. We found that extracellular and cytoplasmic glomerular 4', 6-diamidino-2-phenylindole (
DAPI)-positive areas were clearly consistent with
amyloid deposition in
AL amyloidosis. In contrast, the overlapping staining was not seen in
AA amyloidosis. Therefore, we propose that
DAPI staining readily distinguishes AL renal
amyloidosis from AA renal
amyloidosis as a simple and reproducible histochemical method. J. Med. Invest. 64: 217-221, August, 2017.