Renal Amyloidosis

　　1. Etiology

　　In recent years, scholars have conducted detailed chemical analysis and research on the deposits in the pathological tissue, finding that 85% to 95% of all amyloid deposits are fibrous components, which are the precursor proteins of amyloid substances, soluble in water and low ionic strength buffers, with a molecular weight between 4000 and 25000 Da. To date, more than 20 types of amyloid precursor proteins have been identified, and these proteins have different primary structures, which can exist in both dissolved and fibrous forms. When existing in a fibrous form, X-ray diffraction can reveal that these amyloid fibers have a common core structure, that is, a parallel β-sheet-like structure perpendicular to the long axis of the amyloid fibers, and therefore, some scholars also believe that amyloidosis is a disease of protein secondary structure. Research also found that these proteins not only have etiological significance but also have a direct relationship with clinical manifestations, related diseases, treatment, and prognosis, so it is recommended that clinicians further analyze the chemical composition of amyloid deposits after establishing the diagnosis of amyloidosis. The following briefly introduces several main amyloid precursor proteins.

　　AL protein is an abnormal structure protein derived from monoclonal immunoglobulin light chains or their partial fragments, with a molecular weight of 5000 to 16000 Da, which can be excreted in urine. The most common light chain component is the Lambda (λ) type of light chain, with a few being Kappa (κ) type, the former being about twice as much as the latter. Research has found that not all fragments of the light chain have the same amyloid formation characteristics, and the variable region Vλ is most closely related to amyloidosis, and patients with Vλ monoclonal immunoglobulin are more prone to kidney involvement and less likely to be associated with myeloma. In 90% of patients, the deposited light chain components contain constant region sequences, so clinical tests can use anti-light chain serum that can specifically bind to the constant region for the detection of this disease. For the other 10% of patients whose deposits do not contain the constant region, anti-λ chain or anti-κ chain antisera can be used for detection. AL protein-induced amyloidosis is the most common systemic amyloidosis, and the disease can occur concurrently with B cell clone plasma cell diseases, such as multiple myeloma, lymphoma, and macroglobulinemia. About 15% of AL-type amyloidosis patients have myeloma. Most AL-type amyloidosis patients have a low-grade monoclonal immunoglobulin disease, and a sensitive method such as immunofixation of concentrated urine can detect a monoclonal component in 86% of patients' urine.

　　AA protein derives from the serum amyloid A protein of the circulating acute-phase reactant, with a molecular weight of 4500-9200 Da, and the subunit of the fibrous peptide chain is composed of 76 amino acid N-terminal split fragments. SAA is a high-density lipoprotein synthesized in the liver, and its protein concentration in the blood rises simultaneously with the concentration of C-reactive protein produced by the liver during inflammation. The production of SAA protein is regulated by cytokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF). Benditt et al. reported that the amino acid composition and the sequence of amino acid residues at the amino terminus of AA protein are different from those of AL protein, with the sequence being arginine-serine-phenylalanine-phenylalanine-serine, or serine-phenylalanine-phenylalanine-serine. This AA protein lacks cysteine and threonine components, and the content of proline and valine is also very low, thus determining that AA protein is unrelated to immunoglobulins. Amyloidosis caused by AA protein can be seen in any patient with a persistent serum acute-phase reactant, such as secondary amyloidosis due to chronic inflammation, familial Mediterranean fever, Muckle-Well syndrome, and so on.

　　Amyloid thyroid transport protein is a fibrous amyloid protein deposited in the tissues of diseases such as familial amyloid polyneuropathy, familial amyloid cardiomyopathy, and vitreous amyloidosis. At least 70 variants are known to be associated with amyloidosis at 127 sites of the TTR molecule, among which the most common mutation associated with FAP is the replacement of valine at the 30th position with methionine, and the mutation associated with FAC is the replacement of valine at the 122nd position with isoleucine. It should be noted that in some elderly individuals, systemic amyloidosis involving the heart is due to the prolonged presence of the normal inherent thyroid transport protein in the blood, with the wild-type thyroid transport protein deposited as amyloid protein in the myocardium and other tissues, known as senile systemic amyloidosis.

　　Amyloid apolipoprotein AI is a major component of high-density lipoprotein. Currently, there are 10 known precursor proteins of this protein's amyloidosis, including 7 single-base substitutions, and other variants include insertions or deletions. The disease is an autosomal dominant genetic disease, with clinical manifestations of visceral amyloidosis, mainly myocardial lesions and polyneuropathy. Liver lesions are also extensive but liver function is good. Renal damage is significant, and most eventually develop into renal failure.

　　The amyloid fibrinogen alpha chain mutant encodes amyloidogenic fibrils, and it is known that four mutant types are related to the disease. Among them, two are frameshift mutations, including the deletion of the third base of the codon 524 and the deletion of codon 522, resulting in the replacement of arginine at position 554 with leucine. Other mutations include the replacement of glutamic acid at position 526 with valine. The clinical manifestation is hereditary kidney amyloidosis, but the family history is not obvious. Most patients develop proteinuria or hypertension in middle age, and progress to chronic renal failure in 4 to 10 years.

　　The precursor protein of amyloid beta 2-microglobulin is beta 2-microglobulin, with a molecular weight of about 12,000 Da, which is the constant chain of MHC class I molecules, expressed in all nucleated cells, and exists in a free state in normal circulation. It can be filtered by the glomerulus and reabsorbed and decomposed by the proximal tubule. Amyloidosis of beta 2-microglobulin was first reported in 1980, occurring in patients with long-term hemodialysis. Long-term dialysis, especially hemodialysis, leads to the accumulation of beta 2-microglobulin in the blood. The dialyzer clears little beta 2-microglobulin, and the accumulated beta 2-M deposits in the tendons near the ulnar nerve and wrist joint. Affected bones appear cystic changes, and the clinical manifestations are mainly the movement disorder of the wrist joint, gradually affecting other joints.

　　In addition to the above proteinaceous fibril components, tissue amyloid deposits contain some non-fibrillar components, mainly including serum amyloid P-component, apolipoprotein E, heparin sulfate proteoglycans, and so on.

　　SAP protein is a cytoplasmic glycoprotein, a non-fibrillar amyloid protein with a molecular weight of 23,500 Da. It is produced by liver cells and only decomposed in liver cells, with a half-life of 24 hours in circulation. SAP has a homologous structure with C-reactive protein, but its concentration in blood does not increase during inflammation, which is different from SAA protein. SAP has a specific pentameric structure with a cationic ligand binding site, and monomers can bind to ligands in a calcium-dependent manner. During amyloidosis, SAP in serum remains at a high concentration, suggesting its possible involvement in the pathogenic process of amyloidosis. The structure of SAP pentamers can bind to amyloid proteins and inhibit their degradation. This has been confirmed by using SAP gene knockout mice, showing that SAP promotes amyloidosis, and the deposition rate of amyloid substances significantly decreases in the absence of SAP. Intravenous injection of purified SAP can selectively bind to amyloid deposits, and this characteristic has been applied in clinical practice. Radio-labeled SAP is used to localize and quantify amyloid deposits in patients with amyloidosis.

　　Apolipoprotein E is found in the amyloid deposits of all patients with amyloidosis, and apolipoprotein E4 is closely related to Alzheimer's disease and is also a high-risk genetic factor for other forms of amyloidosis, but its pathogenic mechanism is still unclear. Heparsulfate proteoglycan is a basement membrane component also found in all amyloid deposits, and its pathological role is still unclear. An anion sulfate that can bind to it can reduce the deposition of amyloid fibers in guinea pigs with acquired amyloidosis, and it may be used as an effective therapeutic drug in the future.

　　Second, pathogenesis

　　1. Amyloidosis may be related to abnormal immune function of the body, abnormal protein metabolism, and the denaturation and decomposition of connective tissue. However, it is now considered to be caused by the deposition of a group of proteins that have common characteristics. The excessive production of these proteins aids in their deposition, especially in patients with AL-type amyloidosis complicated by multiple myeloma.

　　2. In secondary amyloidosis and familial Mediterranean fever, some serum AA apolipoprotein synthesized during the acute phase can act as AA amyloid deposits; in amyloidosis caused by β2-M, the increase in serum β2-M levels is due to excessive production or secretion or reduced degradation, but the deposition is unrelated to serum levels. Some believe that the increased serum level of β2-M is sufficient to accumulate in tissues and cause amyloidosis. The possible pathogenesis of Aβ2-M deposition in long-term hemodialysis patients is as follows:

　　(1) The loss of renal function in uremic hemodialysis patients results in a decrease in the filtration of β2-M by the glomerulus and an increase in the accumulation of blood β2-M. Long-term use of general dialyzers for hemodialysis, due to the low clearance of β2-M by copper phthalocyanine membranes and cellulose membranes, can lead to an increase in the concentration of Aβ2-M in the blood. However, switching to PAN membranes, polysulfone membranes, or dimethylpolysiloxane membranes can increase the clearance of Aβ2-M due to the increased convective clearance of Aβ2-M and increased adsorption of β2-M on the membrane surface, thereby reducing the level of β2-M in the blood.

　　(2) Endotoxin contamination in dialysate and the effect of dialysis membranes can activate monocytes/macrophages and lymphocytes, leading to an increase in cytokines such as interleukin-1 (IL-1), tumor necrosis factor (TNF), and transforming growth factor (TGF), which are released into bone matrix and cartilage, promoting the deposition of Aβ2-M in the bone and causing disease. Their effect on bone resorption is greater than that of parathyroid hormone.

　　3. In some amyloid proteins, especially ASC protein or AE protein, due to the substitution of a single amino acid, the deposited protein is different from the normal similar substance, and it is believed that the deposition may be directly related to the molecular biochemical characteristic changes caused by the change in peptide sequence. In AL-type amyloidosis, the deposited light chain is often a hydrolysis fragment of the original light chain, occasionally the original light chain.

　　4. Due to the possible mediation of partial mutation and degradation of amyloid deposition, in β2-M deposition, the involved proteins are more acidic and have higher glycosylation characteristics than normal β2-M, and glycosylated β2-M can cause transient increases in TNF-α, IL-1, and monocyte chemotaxis.

　　5. Indeed, all amyloid proteins are often deposited together with amino sugars and amyloid P substance (i.e., SAP protein). The molecular mechanism of amyloid protein deposition is still under study.

　　Clinically, it often complicates with congestive heart failure, which presents with progressive and refractory attacks. Heart failure caused by amyloidosis is difficult to treat, and some patients are extremely sensitive to digitalis, leading to severe and even fatal arrhythmias, such as if it involves the conduction system, it can cause conduction block, atrial fibrillation, atrial flutter, and ventricular arrhythmias, which are often late manifestations of primary amyloidosis with extremely poor prognosis.

　　Amyloidosis is a systemic disease, involving not only the kidneys but also other organs. Due to the differences in the organs involved, the severity and site of the lesions, the clinical manifestations are also different; secondary cases, due to the differences in the underlying diseases, their clinical manifestations are varied, and there are also cases with no obvious systemic involvement but with renal involvement as the initial manifestation.

　　1. Classification:Amyloidosis has several types, each of which can be distinguished by the immunochemical properties of amyloid protein fibers. These basic characteristics are: β-sheet structure in X-ray diffraction examination; fine fiber non-branching appearance under electron microscopy; apple green birefringence under polarized microscopy after Congo red staining. Based on these biochemical characteristics, combined with pathological features and clinical manifestations, it is divided into 6 types.

　　1, AL type (i.e., primary amyloidosis):Primary amyloidosis refers to amyloidosis with unknown etiology, occurring without the presence of other diseases, mainly affecting the heart, digestive tract, tongue, skin, and nervous system, with 40% involving the kidneys.

　　2, AA type (i.e., secondary amyloidosis):Secondary amyloidosis refers to the occurrence of amyloidosis during the course of other diseases, and common causes include:

　　(1) Chronic infections account for 50%, mostly recurrent chronic suppurative infections such as lung abscess, empyema, bronchiectasis, osteomyelitis, etc.; they can also be seen in infectious diseases such as tuberculosis, syphilis, leprosy, and others.

　　(2) Malignant tumors, such as medullary thyroid cancer, islet cell tumor, etc.

　　(3) Rheumatoid arthritis associated with amyloidosis accounts for 20% to 60%.

　　(4) Diabetes.

　　(5) Bullous pemphigoid.

　　(6) Ulcerative colitis.

　　The main organs involved in secondary amyloidosis are the kidneys, accounting for 25%. In addition, the liver, spleen, and adrenal glands are also common organs involved.

　　3. Plasma cell disease associated with amyloidosis:Multiple myeloma and other plasma cell diseases associated with amyloidosis account for 6% to 15%.

　　4. Hereditary familial amyloidosis:Hereditary familial amyloidosis syndrome is rare, including various diseases, commonly familial Mediterranean fever, an autosomal recessive genetic disease. Glomerular amyloidosis is commonly manifested as proteinuria (often nephrotic syndrome) and progressive renal insufficiency, with symptoms such as recurrent urticaria and deafness. Other conditions include Finnish Amyloidosis, etc. Hereditary familial amyloidosis can be divided into nephrotic type, neuropathy type, and mixed type.

　　5. Localized amyloidosis:Localized amyloidosis refers to amyloid lesions that are only seen in individual organs or tissues, such as the brain, cardiovascular system, skin, and urinary tract. The first two are more common in elderly patients.

　　6. Hemodialysis-related amyloidosis:Long-term hemodialysis patients due to β2-M accumulation often deposit in synovial membranes and long bones, causing cystic bone disease, destructive joint disease, and carpal tunnel syndrome, but rarely deposit in internal organs.

　　Secondly, the manifestations of the kidneys:More than 3/4 of patients with amyloidosis have renal disease manifestations, and the clinical manifestations of renal involvement are divided into 4 stages.

　　1. Preclinical stage (Stage I):There are no自觉 symptoms or signs, and the laboratory tests are also normal. Diagnosis can only be made by renal biopsy. This stage can last for 5 to 6 years.

　　2. Proteinuria stage (Stage II):Seen in 76% of patients, proteinuria is the earliest manifestation. More than half of the patients have high-molecular-weight, low-selective proteinuria, with varying degrees. The degree of proteinuria is related to the deposition site and degree of amyloid protein in the glomeruli, and can manifest as asymptomatic proteinuria that lasts for several years. Microscopic hematuria and cellular casts are rare. Hypertension is present in 20% to 50% of patients, and orthostatic hypotension is a characteristic manifestation of autonomic neuropathy.

　　3. Nephrotic syndrome stage (Stage III):Large amounts of proteinuria, hypoalbuminemia, and edema are common, while hyperlipidemia is less frequent. A few patients only have long-term, small amounts of proteinuria. Renal vein thrombosis is the most common complication of nephrotic syndrome, most of which have an insidious onset and present as refractory nephrotic syndrome. A few cases have an acute onset, with symptoms such as abdominal pain, worsening hematuria, increased proteinuria, and deterioration of renal function. Abdominal X-ray or B-ultrasound examination shows that the kidneys are significantly larger than before. Nephrotic syndrome caused by AA protein accounts for 30% to 40%, and AL protein accounts for 35%. Once nephrotic syndrome appears, the disease progresses rapidly, with a poor prognosis. The survival rate within 3 years is not more than 10%.

　　4. Uremic stage (Stage IV):After nephrotic syndrome, progressive renal function decline occurs, up to half of the patients have azotemia, severe cases die of uremia. Renal tubules and interstitium may be involved occasionally, with the latter manifested as polyuria, even polydipsia. In a few cases, there may be renal glycosuria, renal tubular acidosis, and hypokalemia, among other electrolyte disorders. The development from nephrotic syndrome to uremia takes 1 to 3 years or more. The degree of amyloid deposition in the glomeruli is poorly correlated with renal function.

　　Third, the manifestations of extrarenal organs:

　　1. Primary amyloidosis disease:Common symptoms include weight loss, weakness, and fatigue, and multiple organ involvement is common.

　　(1) The kidneys are the most common, accounting for 50%.

　　(2) The heart (40%) is invaded, causing myocardial lesions, cardiac enlargement, arrhythmia, and conduction block. In severe cases, sudden death may occur. 50% die of congestive heart failure and arrhythmia, which is the most common cause of death in primary AL protein type patients.

　　(3) Gastrointestinal mucosal involvement can cause constipation, diarrhea, malabsorption, and intestinal obstruction, among other symptoms. Submucosal vascular involvement may be accompanied by gastrointestinal bleeding, even massive bleeding leading to death. Tongue involvement may result in macroglossia, with the patient having difficulty speaking and swallowing. When lying on the back, the macroglossia may hang down and produce a loud snoring sound. When the stomach is involved, the symptoms may be similar to those of gastric cancer, with repeated vomiting making it difficult to eat.

　　(4) Autonomic or peripheral nerve involvement (19%) manifests as polyneuritis multiplex, paresthesia of the extremities (reduced sensation and numbness in a glove or sock-like distribution), and hypotonia and decreased tendon reflexes; ulnar nerve damage and peripheral tendons with amyloid deposition may manifest as carpal tunnel syndrome; it can lead to autonomic dysfunction, manifested as orthostatic hypotension, gastrointestinal dysfunction, bladder dysfunction, or impotence, and central nervous system involvement in elderly patients may manifest as dementia.

　　(5) Bone marrow involvement can cause compensatory erythrocytosis, and smooth muscle and skeletal muscle involvement is manifested as muscle weakness.

　　(6) Joint involvement is manifested as multiple joint swelling and pain, or bone cystic changes due to bone involvement.

　　(7) Liver damage is 16%, and purpura of the skin is 5% to 15%.

　　2. Secondary renal amyloidosis disease:The symptoms of kidney disease are often masked by the symptoms of the primary disease, and the liver and spleen are also major organs affected. The liver and spleen may become enlarged, with pain in the liver area. In severe cases, liver function may deteriorate, portal vein pressure may increase, and ascites may occur. Jaundice is rare and is more common in the late stage of the disease. In addition, the adrenal glands are often affected, with the lesion being most severe in the cortical layer near the medulla. The adrenal cortex may become enlarged, often leading to tissue necrosis and functional decline due to adrenal vein thrombosis, manifesting as Addison's disease.

　　3, Renal amyloidosis disease associated with multiple myeloma:The main symptoms are unbearable bone pain, X-ray films show bone destruction or fracture phenomena. Because bone destruction often causes increased blood calcium levels, secondary hyperuricemia, abnormal increase of serum globulin, and the appearance of coagulability protein in urine.

　　4, Senile amyloidosis disease:It often occurs in the brain, heart, pancreas, aorta, seminal vesicle, and bone and joint tissues. Due to the deposition of amyloid protein, the cell function of the deposited organs becomes disordered and dies. The blood vessel walls in the lesion sites show amyloidosis, which is characterized by the inflammation of blood vessels due to the deposition of Congo red-stained amyloid fibers. The involvement of blood vessel walls is a feature of senile amyloidosis, and it is believed that this amyloid protein originates from the circulatory system. Due to different underlying diseases, the chemical structure of amyloid protein also varies.

　　5, Hemodialysis-related amyloidosis disease:Long-term hemodialysis patients have an abnormal increase in the amyloid protein (Aβ2-M) of β2-microglobulin polymers in the blood, which is closely related to the bone and joint complications of the patients, and its clinical manifestations are as follows:

　　(1) Carpal tunnel syndrome: patients may experience pain, numbness, and motor impairment in one or both hands, with a low incidence rate in those who have been on dialysis for less than 5 years, a 13-fold higher incidence rate in those who have been on dialysis for 9 years, and a 100% incidence rate in those who have been on dialysis for more than 17 years. Aβ2-M deposition is present in the carpal tunnel tissue, ulnar nerve, and surrounding tendons sheaths.

　　(2) Amyloid arthritis: the shoulders, hips, knees, wrists, sternoclavicular joints, interphalangeal joints, ankles, elbows, cervical and lumbar joints of long-term dialysis patients can be affected, with the first four being most commonly affected. Joint swelling and pain, functional limitation, stiffness, X-ray films show joint space narrowing, bone destruction, and bone damage near the joints can be seen as cystic translucent areas. When finger joints are involved, trigger finger can be caused by tenosynovitis, and tendon rupture can occur.

　　(3) Pathological fracture: cystic bone damage occurring in the femoral head, neck, or acetabulum can lead to pathological fractures.

　　(4) Extraosseous deposition of Aβ2-M: rare, Aβ2-M can deposit in extraosseous tissues such as the gastrointestinal tract, heart, liver, spleen, lung, adrenal glands, prostate, testicles, etc. The blood vessel walls in the involved areas show deposition of Aβ2-M amyloid protein, and the symptoms caused by different deposition sites are also different.

　　The prevention of this disease should focus on the active treatment of the primary diseases that can induce the disease. In recent years, cases accompanied by tuberculosis and empyema have become rare, indicating that prevention is an effective measure. Limited cases can sometimes be surgically removed; for AL accompanied by myeloma, treatment with alkylating agents and prednisone can relieve symptoms in 50% to 60% of cases, and primary AL can also be treated with the aforementioned therapy or simultaneously with dimethyl sulfoxide and alkylating agents. Colchicine has a positive preventive effect on AA amyloidosis caused by familial Mediterranean fever, but the therapeutic effect of AA on other AL is inconsistent. Supportive therapy helps to extend survival, including the rational use of diuretics to improve cardiac and renal function, and the use of antibiotics to improve the consequences of infection.

　　I. Urine examination:Proteinuria can be seen in the urine, and patients with M protein in the urine also have a large amount of proteinuria. The positive rate of monoclonal abnormal proteins detected in urine examination can reach 86%, and microscopic hematuria is occasionally seen, with granular or fatty casts in the urine sediment.

　　II. Blood biochemistry examination:There is a decrease in fibrinogen, hyperfibrinolysis, and a lack of coagulation factors. Howell-Jolly bodies are found in peripheral blood, indicating spleen involvement. In severe cases, liver function abnormalities may be seen, and jaundice is rare.

　　III. Serum examination:About 2/3 of patients may show monoclonal abnormal proteins in serum electrophoresis or immunoelectrophoresis. Immunoelectrophoresis and immunofixation are sometimes used to determine trace proteins in blood or urine. The measurement of immunoglobulin concentration is helpful for the classification and diagnosis of multiple myeloma. Patients with urine containing Bence-Jones protein can react with antiserum against κ chain and λ chain, but not with any type of immunoglobulin heavy chain.

　　IV. Determination of SAA protein level in blood:AA protein evolves from its precursor SAA protein. An increased concentration of SAA in the blood suggests secondary amyloidosis caused by AA protein. In rheumatoid arthritis, ulcerative colitis, tuberculosis, tumor, and acute phase of chronic infection, SAA is elevated and accompanied by an increase in C-reactive protein. Therefore, the level of SAA can be used to distinguish whether the infection is in the active phase. SAA > 0.2 μg/ml is seen in active inflammation, and after infection control, the level of SAA decreases. In patients with long-term dialysis and bone disease, an abnormally elevated level of β2-M in the blood can help diagnose bone disease in amyloidosis.

　　V. Pathological examination:Pathological examination is the most reliable method for diagnosis, and visceral puncture biopsy greatly improves the pre-death diagnostic rate. In patients with obvious proteinuria, the positive rate of renal biopsy is close to 100%, and post-biopsy hemorrhage is more likely, but less severe than liver biopsy, so it is currently considered that renal biopsy is more advisable than liver biopsy and has become the main method for diagnosing renal amyloidosis. The positive rate of liver biopsy is low, only 50%, and there is a risk of massive hemorrhage, so it should be done with caution. The positive rate of bone marrow biopsy is about 50%, and the collection of rectal mucosal biopsy should be deep, including the固有层 of the mucosa, with a positive rate of 73%. In AL or AA type amyloidosis, the aspirated abdominal wall fat may also show amyloid protein deposition, with a diagnostic positive rate of 70% to 80%. Other possible tissue examination sites include the gums, skin (low sensitivity), gastric mucosa and small intestine. Endoscopic brushing cytology and biopsy can improve the positive rate of gastric examination. The synovial tissue excised after the carpal tunnel is relaxed is definitely positive, but these tissues are usually not used for diagnostic evaluation.

　　The biopsy specimen is treated with 5% potassium permanganate before Congo red staining. AA protein is sensitive to potassium permanganate and has a small affinity for Congo red, resulting in a negative staining test. In contrast, AL protein has a large affinity for Congo red, resulting in a positive staining test. Therefore, this method can be used to differentiate whether the lesion is caused by AA protein or AL protein, thus helping to distinguish between primary and secondary amyloidosis.

　　Bone biopsy is the best method for early diagnosis of Aβ2-M deposition in bone. Potassium permanganate-Congo red staining is positive, and negative staining in AA or AF amyloid proteins helps in differential diagnosis. Under the electron microscope, if amyloid fibers with irregularly arranged, 8-10nm diameter can be seen, it can be diagnosed.

　　1. Optical Microscopy Examination:The histological manifestations of primary and secondary amyloidosis in the kidney are similar. Early changes in the glomeruli are not obvious, and a correct diagnosis can only be made based on special staining. In the glomerular membrane, peritubular capillary wall, and vascular deposits, Congo red staining appears brick red and shows apple green birefringence under polarized microscopy. Hematoxylin-violet staining shows a change in color, and thionine-T staining is visible under ultraviolet light. Similar amyloid deposits can be observed in the rectum, interlobular vessels, small arteries, collecting tubules, and interstitial cells using thick sections. Deposits in the interstitial matrix may be related to tubular dysfunction, such as renal diabetes or damage to tubular reabsorption of HCO3-.

　　On HE stained slides, the glomerular membrane appears as a coagulated eosinophilic substance. With the progression of the disease, the glomeruli become less cellular and are replaced by amyloid deposits. At this stage, it is difficult to distinguish diabetic glomerulosclerosis, light chain deposition disease, and nonspecific chronic glomerulonephritis under standard optical microscopy. In some patients, the capillary wall is significantly thickened, and silver staining is positive and spatulate, indicating false idiopathic membranous nephropathy. In familial Ostertaag variant disease, there are giant cells around the amyloid deposits, and amyloid casts are present in the renal tubules.

　　2. Fluorescence Immunohistochemistry:Their manifestations vary, but the most common is the presence of amorphous aggregates with weak staining of Ig, light chains, and C3 in the capillaries and glomerular membranes. Gallo et al. used fluorescence immunohistochemistry and ant-Ig serum, ant-light chain protein serum, and ant-AA protein serum to differentiate between AA and AL types. Other proteins, including albumin and fibrinogen, are also found in the deposits. The performance of fluorescence immunohistochemistry is not sufficiently specific for diagnosis, and corresponding light chains can be found in the deposits of primary amyloidosis.

　　3. Electron microscopy examination:The ultrastructural manifestation is of great value in the diagnosis of amyloidosis. The characteristic lesion is the presence of fine fibers with a diameter of 8-10nm arranged in a chaotic or bundled manner. Due to its lack of periodicity, it is easily distinguished from collagen fibers. It can appear in the glomerular membrane, subepithelial or subendothelial basement membrane. In mild lesions, only the glomerular membrane is involved. With the progression of the disease, the capillary wall where the amyloid fibers are deposited is also involved. Occasionally, there are needle-like deposits under the endothelium. A group of studies believes that fibrous amyloid deposits are likely to be composed of AA-type amyloidosis, and granular amyloid deposits are likely to be composed of AL-type.

　　Six, Congo red test:This method can be used to indirectly differentiate amyloid AA protein and AL protein, and is a simple and convenient auxiliary diagnostic test. After the amyloid protein is oxidized with 5% potassium permanganate, Congo red staining is added. Since AL protein has a strong affinity for Congo red, it is stained and not easily faded, but AA protein has a poor affinity for Congo red, so it is not easily stained. After injecting a certain amount of Congo red, the absorption rate of normal people is 10% in 1 hour, the absorption rate of glomerulonephritis is 20% in 1 hour, and the absorption rate in nephrosis is 40%. For renal amyloidosis, the absorption rate is 30% in 20 minutes. If the absorption rate is greater than 60% in 1 hour, it is positive. This has little significance for the diagnosis of early primary amyloidosis, as the amyloid substance deposition in the early involved organs is less, and the absorption of Congo red is less, so it is often negative. In addition, when the serum albumin is low in liver disease, it affects the absorption rate; when there is a large amount of proteinuria, the amount of Congo red absorbed in the urine should be excluded when calculating the absorption rate. This method has poor reliability and is now rarely used.

　　Seven, amino acid sequence analysis of amyloid protein:The amino acid composition and the arrangement order of the residues of amyloid protein are helpful in distinguishing AL protein and AA protein.

　　Eight, other examinations:

　　1. X-ray abdominal film, ultrasound examination, or intravenous pyelography:If the renal shadow is enlarged (especially when combined with renal vein thrombosis), it can assist in diagnosis, but if the renal shadow size is normal or reduced in the late stage, it cannot exclude the diagnosis.

　　2. Renal venography:It is helpful in diagnosing renal vein thrombosis.

　　3. Radioisotope scanning:Applied to determine amyloidosis, 99mTc-dimercaptosuccinate (9mTc-DMSA) can be reabsorbed by the proximal renal tubules. When the renal tubules and interstitium are involved, the reabsorption function of the proximal tubules decreases, leading to reduced uptake of 99mTc-DMSA. However, due to the lack of analytical sensitivity, it is not used. The application of 123I-labeled serum amyloid P-component for the diagnosis of AA and AL-type amyloidosis has a promising prospect. There are reports of intravenous injection of radioactive β2-M to detect amyloidosis containing β2-M.

　　4. Two-dimensional echocardiography:There is a high sensitivity to cardiac amyloidosis.

　　Food that cannot be eaten with renal amyloidosis

　　1. Various kinds of wine and beverages (including sweet wine, cola).

　　2. Beef, mutton, dog meat, corn, sweet potatoes, bamboo shoots, dried chili peppers.

　　3. Various vegetables with yellow flowers, such as: potatoes (sweet potatoes), bitter melon, luffa, cucumber, etc. (But watermelon and winter melon can be eaten)

　　4. Potatoes, salted eggs (egg yolk), and drugs or soap containing sulfur. Even after the cure of nephritis, they should not be contacted.

　　First, treatment

　　1. General treatment:During the acute phase, bed rest, sufficient caloric and vitamin supplementation, and wearing elastic stockings and tight clothing may have certain preventive and therapeutic effects. Patients with renal insufficiency should limit protein intake, and patients with nephrotic syndrome should undergo salt restriction and diuretic therapy, commonly using furosemide. When using it, attention should be paid to prevent orthostatic hypotension, and in cases of severe edema, the administration of human serum albumin can temporarily alleviate edema, but the efficacy is short-lived and expensive, and should not be used frequently as a routine. Patients with cardiac amyloidosis are very sensitive to calcium channel blockers and should be avoided. For patients with recurrent heart failure, digoxin can be appropriately used, with the main treatment still being diuretic therapy. For patients with severe heart failure and hypotension, attention should be paid to changes in hemodynamics.

　　2. Special treatment

　　(1) AL protein-related amyloidosis: The key to treating AL amyloidosis lies in inhibiting the proliferation of monoclonal plasma cells, thereby inhibiting the production of immunoglobulin light chains. Prospective study results show that the application of prednisone (prednisone) 0.8mg/(kg?d) + melphalan (melphalan) 0.15mg/(kg?d), administered continuously for 7 days, once every 6 weeks, can reduce or eliminate urinary protein in about 1/3 of patients with nephrotic syndrome, and the renal function of most patients remains stable. There are also studies showing that the combination therapy of melphalan (melphalan) + prednisone (prednisone) is more effective than the use of melphalan (melphalan), prednisone (prednisone) or colchicine alone, and can prolong the survival time of patients. Long-term use of melphalan (melphalan) should be aware of the possibility of leukemogenesis and myelodysplasia. It can also refer to other chemotherapy regimens for multiple myeloma, such as using vincristine, doxorubicin (adriamycin), dexamethasone, etc. It has been confirmed that the use of adrenal cortical hormones alone is ineffective in the treatment of this disease, but if there is acute crescentic glomerulonephritis, corticosteroid pulse therapy can be considered. In addition, if there is adrenal insufficiency after involvement, it is also an indication for the use of glucocorticoids.

　　In recent years, a new anthracycline-like drug, hydroxydaunorubicin, has shown significant chemotherapeutic effects in the treatment of AL amyloidosis and is believed to be applied clinically in the near future. Reports in recent years have shown that the combination of peripheral hematopoietic stem cell transplantation with high-dose melphalan (melphalan 70-120mg/m2 given intravenously as a single dose) has also demonstrated good effects in the treatment of this disease.

　　It should be noted that the regression of amyloidosis is a gradual process. Even if the proliferation of plasma cells is effectively suppressed, the improvement of clinical symptoms or the recovery of organ function still requires several months or even years. The recovery of cardiac amyloidosis is particularly slow. During chemotherapy, attention should be paid to balancing the efficacy of chemotherapy and the further damage to organ function, and the indications should be strictly controlled.

　　(2) AA protein associated amyloidosis: For cases secondary to chronic inflammation or infectious diseases, the primary treatment should be the treatment of the primary disease. In some cases, after controlling the chronic suppurative infection focus or after resection or control of the tuberculosis focus, the progression of the disease can often be stopped or improved, and the deposited amyloid material can be absorbed, resulting in a significant improvement in clinical symptoms and the disappearance of proteinuria. Colchicine is effective for amyloidosis caused by familial Mediterranean fever, with a dose of 1-2g/d, which can reduce fever, shrink the enlarged kidneys, improve renal function, and decrease the level of SAA in the blood. The mechanism of action is not yet clear and may be related to inhibiting the aggregation of inflammatory cells and blocking the deposition of amyloid substances. It is best to adjust the drug dose according to the serum SAA concentration when using this drug. Whether the drug is effective for non-familial Mediterranean fever patients with AA amyloidosis is not yet clear.

　　In 1988, some authors reported that dimethyl sulfoxide (DMSO) can dissolve amyloid fibers, causing the deposition to disappear, reducing interstitial inflammatory lesions in the kidneys, reducing or eliminating urinary protein, improving renal function, decreasing blood creatinine, and increasing creatinine clearance. This drug is an oxygen free radical scavenger and also helps in the repair of renal tissue cells. It is suitable for secondary cases, including those secondary to rheumatoid arthritis. Oral or intravenous injection of 5g, three times a day, can alleviate rheumatoid joint pain, improve activity, and reduce the concentration of SAA and C-reactive protein in the blood. However, there are also reports of inefficacy, and the efficacy needs further observation.

　　British scholars reported that using benzylbutyric nitrogen mustard to treat AA amyloidosis caused by rheumatoid arthritis and juvenile inflammatory arthritis, 2/3 of the patients improved their nephrotic syndrome after treatment, renal function was stabilized or restored, and the survival rate after long-term follow-up was greatly improved.

　　(3) β2-M associated amyloidosis: High-throughput dialyzers can effectively reduce blood β2-M levels. Regular high-flux hemofiltration can remove more β2-M, which is only suitable for patients with stable hemodynamics. Early application can delay and prevent the disease, but it is not helpful for improving the bone disease that has already occurred. For bone and joint pain caused by carpal tunnel syndrome and bone erosion, nonsteroidal anti-inflammatory drugs can be used, and intra-articular injection of corticosteroids can also be applied. For patients with chronic renal failure who develop dialysis-related amyloidosis, the only effective treatment is renal transplantation. After transplantation, the serum β2-M level can decrease rapidly, and clinical symptoms can improve quickly. There are reports that about 20% of patients may develop amyloidosis in the transplanted kidney one year after transplantation, which may be related to the continuous production of amyloid proteins. It is necessary to analyze the relevant etiology to weigh the pros and cons when choosing renal transplantation.

　　3. Renal Replacement Therapy:When renal amyloidosis develops to the stage of uremia, dialysis therapy and renal transplantation are the most effective measures to extend the life of patients. The average survival period of patients undergoing maintenance hemodialysis treatment is much higher than that of those who have not undergone dialysis, but the survival rate reported by different studies varies greatly. For patients with cardiac amyloidosis, hemodialysis should pay special attention to cardiovascular complications such as heart failure, arrhythmias, and hypotension, and attention should be paid to hemodynamic stability when choosing dialysis regimens. Some scholars also believe that hypotension is related to the involvement of amyloidosis in the adrenal glands, and it is recommended to supplement corticosteroids appropriately during hemodialysis. Peritoneal dialysis has a small impact on hemodynamics and helps in the excretion of middle molecular weight light chain proteins, which may be more suitable for this type of patient. Renal transplantation can significantly improve the clinical symptoms of amyloidosis, but the improvement in long-term survival rate is not significant. Active treatment of the primary disease and chemotherapy to reduce the production of amyloid protein are the key to improving the prognosis.

　　II. Prognosis

　　Compared with other glomerular diseases, renal amyloidosis has a poor prognosis, and the survival period is related to the primary disease and the extent and severity of involvement of important organs. The median survival period for those caused by primary AL protein is 1 to 2 years, and standard melphalan plus hormone therapy can extend the survival period by 10 months, but it is difficult to recover kidney and heart function. Long-term follow-up of 841 patients with primary amyloidosis shows that the 1-year survival rate is 51%, 5 years is 21%, and only 4.7% at 10 years. The shortened survival period is strongly correlated with the presence of azotemia. The longest survival period is 22 years for the AL type and 18 years for the AA type. Heart failure, arrhythmias, and sudden death are the main causes for those caused by AL protein, accounting for 63%; the average survival period for those caused by secondary AA protein is 45 months, and only 6% survive for more than 5 years, most of whom die of renal failure, accounting for 35%.