Amyloidosis is a shared name for a number of rare, complex and serious disease entities with an annual incidence in Denmark of about 2 per 100,000. Amyloidosis is caused by extra-cellular deposits of amyloid substance created by accumulation of different misfolded proteins. Accurate characterization of the amyloid protein is essential. Amyloid light chain (AL) amyloidosis is a plasma cell dyscrasia that can be treated with chemotherapy, whereas transthyretin (ATTR) and secondary Amyloid A (AA) amyloidosis are other entities that are not treated within haematology. It is generally recognized that conventional immunohistochemistry has limitations, particular due to unspecific staining. Immune electron microscopy (IEM) and laser dissection microscopy followed by tandem mass spectrometry (LDM-MS) are the new gold standards. It has not been established if one of the methods is superior; each method have some strengths and weaknesses. At Odense Amyloidosis Center, IEM and LDM-MS have been established for standard diagnostics in 2017.
To compare the sensitivity and specificity of IEM and MS for sybtyping amyloid deposits in different organs
We performed a retrospective study of 106 Congo red positive biopsies from a number of different involved organs; heart, kidney, lung, gut mucosa, subcutaneous fat, bone marrow. IEM was performed with gold-labeled antibodies against kappa, lambda, transthyretin and amyloid A.
IEM identified specific staining of amyloid fibrils in 91.6% of the biopsies; in 6 biopsies amyloid fibrils were not identified, and in 2 biopsies the subtype of the amyloid fibrils could not be established. MS identified an amyloigenic protein signature in 104/106 biopsies but in 9 of the biopsies the amyloid subtype could not be clearly identified. Protein subtype was established in 95 biopsies (89.6%). The concordance of the results ranged from 89.6–100% for the different subtypes. Importantly, the combined use of both methods increased the diagnostic sensitivity to 100%. Some variety in performances of the methods was observed on organ level.
In conclusion, we demonstrate that both IEM and LDM-MS are sensitive and specific methods for the identification of amyloidogenic proteins in amyloid deposits in biopsies from various organs.