Amyloidosis: A cancer-derived paraproteinemia and kidney involvement

Systematic review of accuracy of reporting of Congo red-stained amyloid in 2010-2020 compared with earlier

BACKGROUND

Almost always, Congo red-stained amyloid between polariser and analyser is said to show "green birefringence" or "apple-green birefringence". In 2010, we found that not all published images showed green, and not all that did showed only green. This systematic review of more recent papers was to find if there had been any improvement in the accuracy of reporting.

MATERIALS AND METHODS

MEDLINE was searched on 15 March 2021 for papers published between 2010 and 2020 inclusive mentioning amyloid and Congo red. These were examined for descriptions of colours, which were compared with images. Papers were searched for mentions of anomalous colours, errors in physical optics, and misquotation of references about polarisation.

RESULTS

In 374 papers, there were 444 descriptions of colours, with 511 images in 257 papers. The commonest descriptions were apple-green, 249/444 (56%), and green, 105/444 (24%). The description agreed with colours seen in 116/511 images (23%) (previously 64/191, 34%). Green was seen in 342/511 images (67%) (previously 159/191, 83%), but not in 169/511 (33%), although each image was reported to show green. Green alone was seen in 103/511 images (20%) (previously 59/191, 31%), and was combined with at least one other colour in 239/511 (47%). Ten papers included the term anomalous. Eight papers incorrectly said that there was green dichroism, three incorrectly used the term green metachromasia, and two incorrectly mentioned green fluorescence. Twenty-seven papers misquoted references.

CONCLUSIONS

There is widespread and increasing inaccuracy of reporting of colours seen in Congo red-stained amyloid. People persist in saying "green birefringence" or "apple-green birefringence", even when no green is seen, or there are also other colours. Few appear to appreciate that the other colours are genuine, respectable, and helpful, the physical optical principles that explain the colours are now understood, and the best expression to use is anomalous colours.KEY MESSAGE"Green birefringence" and "apple-green birefringence" are inappropriate terms to describe the findings in amyloid stained with Congo red and examined between crossed polariser and analyser, because green is not always seen, and even when it is, other colours are commonly seen as well. The proportions of colour images showing any green and green alone, and the proportion of descriptions that agreed with illustrated colours, significantly decreased in 2010-2020 compared with earlier. The most appropriate and scientific description of the findings is anomalous colours.

Typing of hereditary renal amyloidosis presenting with isolated glomerular amyloid deposition

Background

The commonly used methods for amyloid typing include immunofluorescence or immunohistochemistry (IHC), which sometimes may come with diagnostic pitfalls. Mass spectrometry (MS)-based proteomics has been recognized as a reliable technique in amyloid typing.

Case presentation

We reported two middle-aged patients who presented with proteinuria, hypertension and normal renal function, and both had a family history of renal diseases. The renal biopsies of both patients revealed renal amyloidosis with the similar pattern by massive exclusively glomerular amyloid deposition. The IHC was performed by using a panel of antibodies against the common types of systemic amyloidosis, and demonstrated co-deposition of fibrinogen Aα chain and apolipoprotein A-I in the glomerular amyloid deposits of each patient. Then the MS on amyloid deposits captured by laser microdissection (LMD/MS) and genetic study of gene mutations were investigated. The large spectra corresponding to ApoA-I in case 1, and fibrinogen Aα chain in case 2 were identified by LMD/MS respectively. Further analysis of genomic DNA mutations demonstrated a heterozygous mutation of p. Trp74Arg in ApoA-I in case 1, and a heterozygous mutation of p. Arg547GlyfsTer21 in fibrinogen Aα chain in case 2.

Conclusions

The current study revealed that IHC was not reliable for accurate amyloid typing, and that MS-based proteomics and genetic analysis were essential for typing of hereditary amyloidosis.