Amyloidosis comprises a spectrum of disorders characterized by the extracellular deposition of amorphous material, originating from an abnormal serum protein. The typing of amyloid into its many variants represents a pivotal step for a correct patient management. Several methods are currently used, including mass spectrometry, immunofluorescence, immunohistochemistry, and immunogold labeling. The aim of the present study was to investigate the accuracy and reliability of immunohistochemistry by means of a recently developed amyloid antibody panel applicable on fixed paraffin-embedded tissues in an automated platform. Patients with clinically and pathologically proven amyloidosis were divided into two cohorts: a pilot one, which included selected amyloidosis cases from 2009 to 2018, and a retrospective one (comprising all consecutive amyloidosis cases analyzed between November 2018 and May 2020). The above-referred panel of antibodies for amyloid classification was tested in all cases using an automated immunohistochemistry platform. When fresh-frozen material was available, immunofluorescence was also performed. Among 130 patients, a total of 143 samples from different organs was investigated. They corresponded to 51 patients from the pilot cohort and 79 ones from the retrospective cohort. In 82 cases (63%), fresh-frozen tissue was tested by immunofluorescence, serving to define amyloid subtype only in 30 of them (36.6%). On the contrary, the automated immunohistochemistry procedure using the above-referred new antibodies allowed to establish the amyloid type in all 130 cases (100%). These included: ALλ (n = 60, 46.2%), ATTR (n = 29, 22.3%), AA (n = 19, 14.6%), ALκ (n = 18, 13.8%), ALys (n = 2, 1.5%), and Aβ2M amyloidosis (n = 2, 1.5%). The present immunohistochemistry antibody panel represents a sensitive, reliable, fast, and low-cost method for amyloid typing. Since immunohistochemistry is available in most pathology laboratories, it may become the new gold standard for amyloidosis classification, either used alone or combined with mass spectrometry in selected cases.

β2-microglobulin-related (Aβ2M) amyloidosis (dialysis-associated amyloidosis) is a common complication in long-term dialysis patients. An increased concentration of β2-microgloblin (β2-m) in the serum appears to be a prerequisite for Aβ2M amyloidosis, in turn causing Aβ2M amyloid deposition predominantly in the osteoarticular tissue. There are few reports, however, of Aβ2M amyloid deposition in non-dialysis patients. We describe an atypical case of a non-dialysis patient with Aβ2M amyloid deposition in bladder cancer. A Japanese man in his 80s with no history of dialysis was admitted for transurethral resection of bladder cancer. Histopathological analysis revealed a small amount of amyloid deposition in the small-vessel wall of both the peripheral urothelial carcinoma and necrotic area. Amyloid typing by immunohistochemistry was strongly positive for anti-β2-m antibody, and β2-m was most frequently detected in laser microdissection-liquid chromatography tandem mass spectrometry. Although Aβ2M amyloidosis was expected, contrary to this, the patient's serum β2-m was only 4 mg/L, although his urine β2-m level was increased at 1340 mg/L. The unique findings observed in our patient may contribute to the elucidation of the novel pathogenesis of Aβ2M amyloid fibril formation that is distinct from conventional Aβ2M amyloidosis.

Accumulation of amyloid fibrils from β2-microglobulin (β2M) was first recognized as a characteristic osteoarticular complication in long-term hemodialysis (HD) patients and called "HD-related amyloidosis" (HRA). However, this syndrome can also be observed in end-stage renal diseases (ESRD) patients undergoing peritoneal dialysis, and even in patients with chronic renal failure before the initiation of dialytic therapy, suggesting that HD is not a direct cause but that accumulation of β2M or some β2M-associated molecules in the body is a common pathogenesis. Currently the term "dialysis-related amyloidosis" (DRA) is widely used for β2M-amyloid (Aβ2M) amyloidosis associated with ESRD, although DRA patients consist mostly of those undergoing long-term HD. Factors other than β2M accumulation also play a role in the formation/local deposition of Aβ2M and disruption of tissue architecture. Conformational changes of β2M by misfolding/unfolding, and promoting/inhibitory effects induced by other coexisting molecules, advanced glycation and oxidation, and direct cell toxicity have also been documented. Two technological improvements of HD have been the keys to prevent the development and progression of DRA: the efficient removal of β2M by using high-flux membranes, high-volume convection and adsorptive column/membrane, as well as the use of biocompatible membranes and dialysates (eg, ultrapure and acetate-free dialysates) have minimized both inflammation and β2M production. Epidemiologically, a decrease in the incidence of DRA has recently been reported; however, longer survival of HD patients may contribute to the development of more DRA, though with a delayed onset. In this article, we describe the pathogenesis of DRA, the strategies developed for its prevention and minimization, and the favorable epidemiological data achieved by these efforts.

Hereditary amyloid neuropathy includes hereditary ATTR, hereditary AGel, hereditary AApoAI, and hereditary Aβ2M amyloidosis. Among these diseases, hereditary ATTR is the most common type of amyloidosis caused by mutation in the transthyretin (TTR) gene. Hereditary ATTR amyloidosis is a life-threatening, multi-symptom, gain-of-toxic-function disease that may present with peripheral neuropathy, autonomic neuropathy, cardiomyopathy, ophthalmopathy, and/or leptomeningeal amyloidosis. In addition to the clinical symptoms described above, proven amyloid deposition in biopsy specimens and identification of disease-causing mutations in the TTR gene are necessary to establish the diagnosis. Deposition of amyloid in tissue can be demonstrated by Congo red staining of biopsy materials. Liver transplantation has been shown to be an effective therapeutic strategy for ameliorating hereditary ATTR amyloidosis, however, large numbers of patients are not suitable transplant candidates because of their age and/or advanced disease status. Recently, the clinical effects of TTR tetramer stabilizers, tafamidis and diflunisal, were demonstrated in randomised clinical trials, and tafamidis has been approved for the treatment of hereditary ATTR amyloidosis in European countries and in Japan. With the availability of disease-modifying therapies, early diagnosis and therapy become increasingly important in ATTR amyloidosis.