**3.4 Dialysis-related amyloidosis (Aβ2M)**

β2M is a light chain component of the major histocompatibility complex (MHC) class I molecules. It is found in patients on dialysis and is rarely seen in renal failure patients who have not undergone dialysis. Since β2M is catabolized in the kidney, this protein may accumulate in renal failure patients. Conventional dialysis membranes do not remove this protein, thus dialysis-related β2M deposits occur in dialysis patients. Deposits occur mostly in the carpal ligaments, synovium, and bone. Other organs such as the heart, gastrointestinal tract, liver, lungs, prostate, adrenal glands, and tongue can be affected. These days, we use polyamide high-flux membranes to remove β2M, resulting in a lower incidence of this type of amyloid.

### **3.5 Amyloid β (Aβ) protein**

Aβ protein comes from the proteolysis of an amyloid precursor protein known as transmembrane glycoprotein and accumulates as plaque in the cerebral cortex and in the blood vessel. Deposits within the blood vessels cause CAA, which induces progressive cognitive decline and lobar hemorrhage. The most well-known disease related to Aβ is Alzheimer's disease. Rarely, familial Alzheimer's disease, which occurs in an autosomal dominant pattern, is seen. In addition, by about age 50, Down syndrome patients present with amyloid deposits in the brain similar to those of patients with Alzheimer's disease. Furthermore, a very rare form of hereditary cerebral hemorrhage with amyloidosis occurring in an autosomal dominant pattern has been reported.

Clinical symptoms are mostly nonspecific and may include headache, general weakness, edema, and weight change. Symptoms may also depend on the location and amount of amyloid deposition. Amyloid deposition in the heart causes arrhythmia, heart failure, or abnormal electric rhythm. Amyloid in the kidney eventually induces renal failure with proteinuria and uremia. If amyloid deposits within the blood vessels, it creates ischemic or hemorrhagic condition for the organ. Amyloid deposition also mimics arthritis and peripheral neuropathy. Within the brain, it causes cognitive and memory disorders seen in Alzheimer's disease or prion diseases. Localized deposition in the gastrointestinal tract has nonspecific gastrointestinal symptoms, such as dyspepsia or diarrhea. Since clinical symptoms are nonspecific, and most of the amyloid types can cause similar clinical features in the same organ; the clinical approach to amyloidosis is very limited. Therefore, a pathologic diagnosis of amyloidosis is critical.

#### **4. Pathologic findings**

Amyloid deposition is seen in the same manner within the same tissue no matter what protein it contains, except in a few cases. Grossly, amyloidosis deposition can appear as nodules and organomegaly, and sometimes it can show a pale gray to waxy color change with firm consistency. Microscopically, bright pink amorphous material deposition in extracellular space is most commonly observed under conventional hematoxylin–eosin stain. Peculiar intracellular and spheroid type amyloid depositions may be seen, but they are rare.

Since the adventitious discovery by Hans Hermann Bennhold in 1922, Congo red stain has been the gold standard of confirming the presence of amyloid protein. When properly stained, the amyloid imparts red, orange, or salmon pink color. The subsequent demonstration of apple-green birefringence confirms the diagnosis of amyloidosis. However, this two-step method still suffers low sensitivity, specificity and reproducibility and heavily depends on the interpretation of highly

**65**

*Pathologic Findings of Amyloidosis: Recent Advances DOI: http://dx.doi.org/10.5772/intechopen.84268*

complicating the interpretation.

**4.1 Heart**

**4.2 Kidney**

experienced pathologists. For instance, aside from the inherent sampling error, negative birefringence on positive Congo red stain may result in a false-negative result, even if the stained material actually contains amyloid. This "polarization shadow" can be overcome by rotating the slide table, which may detect additional small amount of amyloid protein. The intensity of the stain is also significantly affected by the washing process in the staining protocol, resulting in low reproducibility and mandating the use of positive control tissue. In addition, Congo red also stains collagen, elastin, or even non-fibrillary materials such as eosinophils, further

To overcome such limitations of Congo red stain, additional filters such as a fluorescein isothiocyanate (FITC) or Texas red filter can be used [6]. These filters can augment the weak signal from Congo red into red fluorescence, greatly improving the detection sensitivity. Additional fluorochrome dyes, such as thioflavin T, can also be recruited. The stain becomes highly fluorogenic only when they are bound to amyloid, which imparts a yellow-green fluorescence when it is examined under fluorescence microscopy. Because both fluorescence filters and dyes are not entirely specific for amyloid, they should be used as adjunct in the context of Congo red stain. In conclusion, the light microscopic diagnosis of amyloidosis pertains not only to the on–off signal but also to staining techniques, specimen alignment under

polarized light, fluorescence microscopy, and experience of the pathologist.

still specific features for specific organs, as will be discussed below.

inducing arrhythmia, restrictive cardiomyopathy, and heart failure.

Generally, histological features are similar throughout the organ, but there are

Heart amyloidosis is induced by various types of amyloid. AL type is the most common amyloid found in the heart, while wtATTR, which causes systemic senile amyloidosis, is the second most common amyloid in the heart. Mostly, gross features will be normal unless it is late-stage amyloidosis. Minimal to mild enlargement of the heart, along with pale and waxy changes on the external surface, can be seen. Within the heart, ventricular wall concentric thickening, including that of the septum, is seen. The epicardium, endocardium, and valves can show nodular deposits. Histologically, there is no definite pattern of amyloid deposition based on the type of amyloid, and it normally shows blight pink amorphous deposition, showing an infiltrative pattern within the interstitium. Expanding to the myocardium can cause atrophy of myocardial muscle. Also, arteriolar deposition can be seen in AL amyloidosis. Depending on the site of deposition and amount of deposition, it can cause conduction abnormality

The kidney is the most common organ where amyloid deposits. Various types of amyloid deposits can occur, but AA and AL type amyloids are the most common amyloid types seen in the kidney. Grossly, the kidney is firm, pale, and waxy. The size can vary between normal, enlarged, or small; if amyloid deposits within the arteries or arterioles and causes ischemia, the kidney becomes small. Histologically, there is no type-specific pattern. Amorphous bright pink deposits are mostly seen in the mesangium and capillary wall (**Figures 1** and **2**). In addition, interstitial peritubular tissue, arteries, and arterioles can be affected. Capillary wall thickening and mesangial expansion are seen. Sometimes, amyloid deposits protrude to the basement membrane of glomerular capillaries, showing discontinuity of the membrane. Expansion of amyloid within the mesangium eventually causes capillary obstruction and renal failure. Proteinuria is a very common finding among patients with kidney amyloidosis.

#### *Pathologic Findings of Amyloidosis: Recent Advances DOI: http://dx.doi.org/10.5772/intechopen.84268*

experienced pathologists. For instance, aside from the inherent sampling error, negative birefringence on positive Congo red stain may result in a false-negative result, even if the stained material actually contains amyloid. This "polarization shadow" can be overcome by rotating the slide table, which may detect additional small amount of amyloid protein. The intensity of the stain is also significantly affected by the washing process in the staining protocol, resulting in low reproducibility and mandating the use of positive control tissue. In addition, Congo red also stains collagen, elastin, or even non-fibrillary materials such as eosinophils, further complicating the interpretation.

To overcome such limitations of Congo red stain, additional filters such as a fluorescein isothiocyanate (FITC) or Texas red filter can be used [6]. These filters can augment the weak signal from Congo red into red fluorescence, greatly improving the detection sensitivity. Additional fluorochrome dyes, such as thioflavin T, can also be recruited. The stain becomes highly fluorogenic only when they are bound to amyloid, which imparts a yellow-green fluorescence when it is examined under fluorescence microscopy. Because both fluorescence filters and dyes are not entirely specific for amyloid, they should be used as adjunct in the context of Congo red stain. In conclusion, the light microscopic diagnosis of amyloidosis pertains not only to the on–off signal but also to staining techniques, specimen alignment under polarized light, fluorescence microscopy, and experience of the pathologist.

Generally, histological features are similar throughout the organ, but there are still specific features for specific organs, as will be discussed below.

#### **4.1 Heart**

*Amyloid Diseases*

**3.4 Dialysis-related amyloidosis (Aβ2M)**

**3.5 Amyloid β (Aβ) protein**

has been reported.

**4. Pathologic findings**

depositions may be seen, but they are rare.

β2M is a light chain component of the major histocompatibility complex (MHC)

Aβ protein comes from the proteolysis of an amyloid precursor protein known as transmembrane glycoprotein and accumulates as plaque in the cerebral cortex and in the blood vessel. Deposits within the blood vessels cause CAA, which induces progressive cognitive decline and lobar hemorrhage. The most well-known disease related to Aβ is Alzheimer's disease. Rarely, familial Alzheimer's disease, which occurs in an autosomal dominant pattern, is seen. In addition, by about age 50, Down syndrome patients present with amyloid deposits in the brain similar to those of patients with Alzheimer's disease. Furthermore, a very rare form of hereditary cerebral hemorrhage with amyloidosis occurring in an autosomal dominant pattern

Clinical symptoms are mostly nonspecific and may include headache, general weakness, edema, and weight change. Symptoms may also depend on the location and amount of amyloid deposition. Amyloid deposition in the heart causes arrhythmia, heart failure, or abnormal electric rhythm. Amyloid in the kidney eventually induces renal failure with proteinuria and uremia. If amyloid deposits within the blood vessels, it creates ischemic or hemorrhagic condition for the organ. Amyloid deposition also mimics arthritis and peripheral neuropathy. Within the brain, it causes cognitive and memory disorders seen in Alzheimer's disease or prion diseases. Localized deposition in the gastrointestinal tract has nonspecific gastrointestinal symptoms, such as dyspepsia or diarrhea. Since clinical symptoms are nonspecific, and most of the amyloid types can cause similar clinical features in the same organ; the clinical approach to amyloidosis is very limited. Therefore, a pathologic diagnosis of amyloidosis is critical.

Amyloid deposition is seen in the same manner within the same tissue no matter what protein it contains, except in a few cases. Grossly, amyloidosis deposition can appear as nodules and organomegaly, and sometimes it can show a pale gray to waxy color change with firm consistency. Microscopically, bright pink amorphous material deposition in extracellular space is most commonly observed under conventional hematoxylin–eosin stain. Peculiar intracellular and spheroid type amyloid

Since the adventitious discovery by Hans Hermann Bennhold in 1922, Congo red stain has been the gold standard of confirming the presence of amyloid protein. When properly stained, the amyloid imparts red, orange, or salmon pink color. The subsequent demonstration of apple-green birefringence confirms the diagnosis of amyloidosis. However, this two-step method still suffers low sensitivity, specificity and reproducibility and heavily depends on the interpretation of highly

class I molecules. It is found in patients on dialysis and is rarely seen in renal failure patients who have not undergone dialysis. Since β2M is catabolized in the kidney, this protein may accumulate in renal failure patients. Conventional dialysis membranes do not remove this protein, thus dialysis-related β2M deposits occur in dialysis patients. Deposits occur mostly in the carpal ligaments, synovium, and bone. Other organs such as the heart, gastrointestinal tract, liver, lungs, prostate, adrenal glands, and tongue can be affected. These days, we use polyamide high-flux membranes to remove β2M, resulting in a lower incidence of this type of amyloid.

**64**

Heart amyloidosis is induced by various types of amyloid. AL type is the most common amyloid found in the heart, while wtATTR, which causes systemic senile amyloidosis, is the second most common amyloid in the heart. Mostly, gross features will be normal unless it is late-stage amyloidosis. Minimal to mild enlargement of the heart, along with pale and waxy changes on the external surface, can be seen. Within the heart, ventricular wall concentric thickening, including that of the septum, is seen. The epicardium, endocardium, and valves can show nodular deposits. Histologically, there is no definite pattern of amyloid deposition based on the type of amyloid, and it normally shows blight pink amorphous deposition, showing an infiltrative pattern within the interstitium. Expanding to the myocardium can cause atrophy of myocardial muscle. Also, arteriolar deposition can be seen in AL amyloidosis. Depending on the site of deposition and amount of deposition, it can cause conduction abnormality inducing arrhythmia, restrictive cardiomyopathy, and heart failure.

#### **4.2 Kidney**

The kidney is the most common organ where amyloid deposits. Various types of amyloid deposits can occur, but AA and AL type amyloids are the most common amyloid types seen in the kidney. Grossly, the kidney is firm, pale, and waxy. The size can vary between normal, enlarged, or small; if amyloid deposits within the arteries or arterioles and causes ischemia, the kidney becomes small. Histologically, there is no type-specific pattern. Amorphous bright pink deposits are mostly seen in the mesangium and capillary wall (**Figures 1** and **2**). In addition, interstitial peritubular tissue, arteries, and arterioles can be affected. Capillary wall thickening and mesangial expansion are seen. Sometimes, amyloid deposits protrude to the basement membrane of glomerular capillaries, showing discontinuity of the membrane. Expansion of amyloid within the mesangium eventually causes capillary obstruction and renal failure. Proteinuria is a very common finding among patients with kidney amyloidosis.

#### **Figure 1.**

*Mesangium depositions of homogeneously bright pink material in kidney, H&E stain.*

**Figure 2.** *Mesangium deposition of amyloid in kidney, ALλ type in immunofluorescence.*
