Renal amyloidosis with emphasis on the diagnostic role of electron microscopy

ABSTRACT

Our understanding of renal diseases with structured deposits has improved in the last two decades with the development of new diagnostic techniques that also changed the role of ultrastructural pathology in diagnostic decision-making. This review article addresses the current role of electron microscopy in the evaluation of structured deposits and discusses the impact of new developments. The diagnosis in a subset of structured deposits, amyloidosis, relies on morphologic and tinctorial characteristics at the light microscopic level. Congo red staining of tissue with demonstrable birefringence upon polarization has been regarded as the mainstay during tissue evaluation; however, there are pitfalls that must be considered, and electron microscopy remains a crucial adjunct investigative tool. Ultrastructurally the amyloid fibrils are unique with their characteristic appearance. They are randomly arranged, rigid, criss-crossing, non-branching, 7–15 nm (0.07–0.15 um) in diameter and of variable length. The morphology of fibrils is very similar in the different types of amyloidosis. By scanning electron microscopy amyloid fibrils appear artfully displayed. Immunofluorescence and immunohistochemical stains can be used to characterize the type of amyloidosis while mass spectroscopy is extremely useful in cases where typing of the amyloid using the above-mentioned techniques is difficult or equivocal.

KEYWORDS:

• Amyloid
• ultrastructure
• fibrils
• electron microscopy
• Congo red
• Thioflavin T
• fibrillary glomerulopathy

Key points

• The diagnosis of amyloidosis may be subtle and may require ultrastructural confirmation.

• Thioflavin T stain is more sensitive than Congo red.

• The ultrastructural appearance of amyloid is characteristic with randomly disposed, disorganized, tangled, non-branching fibrils measuring 7–15 nm in diameter.

• There is some variability in the ultrastructural appearance of amyloid fibrils, mainly their disposition and overall arrangement.

• One of the drawbacks in the diagnosis of amyloidosis by electron microscopy is sampling.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.