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Practical information on the diagnosis and treatment of generalized amyloidoses
Key words: amyloidosis, immunohistochemical classification, therapy of amyloid diseases, protein storage diseases
Practical Advice in Diagnosis and Treatment of Systemic Amyloidoses
The amyloidoses belong to the protein storage diseases and are subdivided into many different amyloid syndromes which comprise clinically divergent amyloid diseases. Every clinical amyloid syndrome is further subdivided into individual amyloid diseases of which more than a hundred are known to date. In order to avoid misdiagnoses, a negative result requires special attention and professional expertise. This overview outlines the diagnosis and management of the most important amyloidoses and includes both, diseases which can be successfully treated and others which are susceptible to therapy as well as some which are hardly influenced by any treatment at present. In addition, this article also mentions other protein thesaurosis which do not represent amyloidoses.
Key words: Amyloidosis, immunohistochemical classification, therapy of amyloid diseases, protein storage diseases
The amyloidoses represent protein storage diseases caused by the deposition of amyloids. Amyloids are abnormally folded fibrillar proteins of very different types, which are mainly stored extracellularly in various tissues and organs. With constant accumulation, these proteins can cause severe functional disorders of the organs up to and including organ failure. A large number of different clinical syndromes are known which are characterized by the incorporation of chemically different amyloid fibril proteins. New findings have significantly improved both the diagnosis and the therapeutic options for a whole range of these diseases. Therefore, some recommendations for the diagnosis and therapy of amyloidoses should be given here, which correspond to the current state of knowledge. Non-amyloid protein storage diseases are also briefly discussed here.
Diagnosis of amyloid deposits
Amyloid can be microscopically recognized directly on the histological section in the form of homogeneous, eosinophilic and relatively cell-free protein masses. As shown in Table 1, the evidence for the presence of amyloid is provided by the classic Congo red staining in the modification of Puchtler et al. (13) provided. With the help of this coloring, amyloid is colored red under the light microscope and glows yellow-green in polarized light. This color is pathognomonic for amyloid and the "gold standard" in amyloid diagnostics (5, 12). An assisting criterion is the amyloid fibrils that can be recognized by an electron microscope. Therefore, protein fibrils can only be regarded as amyloid if they optically show the green birefringence.
Another characteristic of the amyloid fibril is its b-sheet structure, the representation of which is of no importance for routine diagnostics, after all, this structure conveys the proteinase resistance and thus the pathogenicity in the organism. The step-by-step procedure for diagnosis is illustrated in the graphic.
Improvement of diagnostics
The amyloid detection has been improved by increasing the sensitivity, which is based on the combination of immunohistochemistry and Congo red, to such an extent that even the very finest amyloid threads, which are often overlooked in the usual Congo red coloring, are already detectable at the onset of amyloidosis, i.e. at one time , in which the clinician may already recognize the first symptoms and express the suspicion of amyloidosis (11). This method gives the clinician the opportunity to intervene therapeutically very early on at the onset of amyloidosis, i.e. before irreversible organ damage occurs. Above all, this method helps to reliably diagnose the often overlooked small amyloid deposits and thus to avoid a false-negative diagnosis. Sample errors can be significantly reduced by examining a series of sections from the same paraffin block (11).
Another possible improvement in diagnostics can come from scintigraphy, in which ideally all amyloid deposits in the body can be marked and detected with an intravenously administered radioactive substance (6). However, this evidence is not yet commercially available.
The type of biopsy
If generalized amyloidosis is suspected, a deep rectal biopsy (with submucosa) is recommended. This ensures a high level of accuracy (around 85 percent). Sampling from affected organs, such as the kidneys, heart, nerves, mucous membrane of various organs and outer skin can sometimes increase the accuracy (by 95 percent), but are associated with a higher risk. The subcutaneous fat tissue biopsy is an inexpensive, simple and always repeatable alternative that can be easily carried out as an entry-level diagnosis anywhere and does not require anesthesia in the child as is the case with endoscopic biopsy. With the help of this method, about 80 percent of generalized amyloidoses, usually AA and AL amyloidoses, can be detected. Since amyloidoses, especially of the AL and Ab2m types, can lead to carpal tunnel syndrome (not infrequently as an initial symptom), the excisate obtained during the operation should always be examined for amyloid.
A number of autosomal inherited amyloid syndromes are associated with amino acid exchanges at the protein level and point mutations at the gene level, which segregate with the clinical picture and therefore represent the causes of these diseases. These mutations can be reliably identified by appropriate analyzes at the protein or gene level. Corresponding analyzes are essential prior to therapy for certain autosomal dominant transthyretin amyloidoses and are therefore available as a routine service (1, 12). Certain amino acid exchanges can be represented at the protein level using the RFLP method (restriction fragment length polymorphism), as illustrated in Figure 1.
Classification of amyloid syndromes
The biochemical analysis of the amyloid fibril proteins has identified very different amyloidogenic proteins. These proteins correlate with clinical amyloid syndromes. They have therefore been used successfully for the classification of amyloids and amyloidoses (2, 4, 9, 10, 12). A certain protein causes a defined amyloid syndrome; however, this can include very different individual amyloid diseases. Common amyloid syndromes are summarized in Table 2.
The chemical amyloid classification is only carried out in a few special laboratories - mainly for scientific purposes - because of its high level of effort. The immunohistochemical classification of the various amyloid syndromes carried out on the tissue section, on the other hand, is available as a routine service in some specialized laboratories and is usually carried out on tissue sections fixed in formalin and embedded in paraffin with the help of poly- and monoclonal antibodies that were produced against amyloid fibril proteins (2, 4 , 10, 12). A typical example of immunohistochemical classification is shown in the graphic.
Clinical amyloid syndromes and therapy
The following is a list of some of the most important syndromes that the doctor has to deal with in practice and that he should be aware of (Table 2). More rare amyloid syndromes can be found in review articles (1, 2, 4, 12).
Amyloidosis of immunoglobulin origin
Amyloid fibrils can be formed from monoclonal immunoglobulin fragments (2, 9, 12) that are synthesized by B-cell neoplasms. These include multiple myeloma, Bence Jones plasmacytoma and related diseases, but also local plasmacytomas, non-Hodgkin lymphomas and so-called benign monoclonal gammopathy (MGUS, monoclonal gammopathy of undetermined significance). About ten percent of all patients with monoclonal gammopathy develop immunoglobulin-type amyloidosis (AIg). The organ distribution of the amyloid is very heterogeneous. Localized forms, organ-limited, but also generalized forms can occur (1, 2, 12). Above all, the variable part of the l-light chain, less often the k-light chain and, very rarely, defective heavy chains are deposited. The organ distribution of the generalized form generally includes the heart, spleen, liver, nerves, skin and connective tissue. The kidney can also be affected. The prognosis of the heart, kidneys and nerves is particularly unfavorable. The disease is recognized by unexplained severe weight loss with severe impairment in performance, restrictive cardiomyopathy, nephropathy, proteinuria, tendency to bleed, macroglossia (Figure 3), polyneuropathy and sometimes doughy, subepithelial amyloid tumors. So far, the proteins in the amyloid conformation cannot be eliminated therapeutically. Therefore, all therapeutic attention is directed to the inhibition of further amyloid apposition. It is therefore the therapeutic goal to suppress or even eradicate the development of monoclonal B-cell dyscrasia. This goal can only be partially achieved today. Impulse therapy with melphalan and prednisone is effective in some cases (12). In individual cases, high-dose therapy with melphalan i.v. and subsequent stem cell infusion, and the first encouraging results, which, however, require further confirmation. If the B-cell neoplasia is suppressed, further apposition of the amyloid is slowed down or even prevented. In rare cases, the Ig-type amyloid can also completely regress. In more recent times, iodododoxorubicin, which binds directly to the amyloid, has even been able to achieve a significant reduction in amyloid substance in some cases, perhaps by inhibiting apposition. However, this therapy is relatively toxic and is not yet generally available in our country.
Amyloidosis of serum amyloid A origin
In most cases, AA amyloidosis is the result of repeated acute exacerbating chronic inflammations. These can be autoimmune in nature, such as rheumatoid arthritis in children and adults, psoriatic arthritis or Crohn's disease and other chronic inflammatory bowel diseases (IBD). It can also be bacterial in nature, such as bronchiectasis, TB, leprosy, cystic fibrosis, and decubitus. The inflammation can also be genetic (familial Mediterranean fever, Muckle-Wells syndrome, periodic fever and arthritis) or neoplastic (nephroid carcinoma, Hodgkin's disease). In rare cases, AA amyloidosis occurs without a known underlying disease. In all of these diseases, attention should be paid to proteinuria in order not to miss a biopsy diagnosis.
As amyloid A (AA), the N-terminal fragment of the most sensitive acute phase protein SAA (serum amyloid A protein) is mainly stored in the vessel walls of arterioles and capillaries. Functional symptoms appear primarily as a result of amyloid deposits in the glomerula (Figure 2) and in the intestine, with the result of proteinuria, nephrosis and kidney failure as well as severe digestive disorders, sometimes with malabsorption. Juvenile chronic arthritis (JCA) and systemic vasculitis are the most common causes of AA amyloidosis in children in Germany today. Another group with this form of amyloidosis is found in Turkish and ethnic Mediterranean children and adults with episodic core symptoms such as fever, peritonitis-like abdominal pain and arthritis. Familiar Mediterranean fever (FMF) must be considered early on, as every third child with FMF dies of the consequences of progressive AA amyloidosis without treatment. With a consequent colchicine prophylaxis, the occurrence of amyloidosis can be almost completely suppressed (15). Since JCA-related amyloidosis is expected to be fifty percent lethal at diagnosis, risk factors must be identified early and an early diagnosis sought (11), because regression of AA amyloidosis can only be expected with consistent early therapy. However, gold therapy should be avoided if amyloidosis is suspected. Aggressive treatment of the underlying disease with chlorambucil led to a significantly better survival rate (11). SAA or CRP concentration determinations serve as course parameters for the response to the therapy. This also applies to adults, in whom rheumatoid arthritis (RhA), along with other inflammatory diseases, is the main underlying disease of AA amyloidosis. The frequency of AA amyloidosis is given differently for severe forms of RhA in different countries, with values from five percent to ten percent being described. For severe forms of psoriatic arthritis, five percent are given, and for severe ankylosing spondylitis (SpA), about two percent are given. In Germany these numbers are lower, in Poland and especially in Finland they are higher. In the United States, the prevalence is well below half a percent with no knowledge of the causes that could explain this difference.
The therapy of AA amyloidosis in adults also consists in suppressing the inflammation as early as possible before irreversible organ damage occurs.
Since preclinical stages of AA amyloidosis can only be found with the help of biopsies, the working group of the Rheumatism Clinic in Oberammergau has created an activity index for the indication of a biopsy, bundling the following inflammation parameters (with the specified limit values): ESR> 45 mm nW, CRP > 50 mg / l, albumin < 55,7="" rel%,="" a2-globulin=""> 11.6 rel%. Based on the results obtained, a biopsy diagnosis was initiated if three of these criteria were met (work in preparation). With the help of these parameters, biopsies can be carried out in a more targeted manner.
Early treatment of the underlying disease can significantly improve renal amyloidosis if the serum creatinine level is still normal. A serum creatinine value above 1.5 mg / dl indicates irreversible kidney damage. The extent of the proteinuria plays a subordinate role. According to the experience of the Rheumatism Clinic in Oberammergau, methotrexate seems to be quite effective in the treatment of AA amyloidosis in the context of rheumatic diseases compared to other basic therapeutic agents, including alkylating agents. Kidney transplantation has proven itself in amyloid-related kidney failure. However, if the underlying inflammatory disease persists, the transplanted kidney may show AA amyloid again after years. In Crohn's disease, effective anti-inflammatory drug therapy is most likely to lead to a decrease in the SAA and thus to a decrease in amyloid deposits. Surgical removal of the Crohn's manifestation can have a similar effect. In addition to disappointing follow-up observations, remissions have even been described.
Amyloidoses of transthyretin origin
The generalized amyloidoses of transthyretin (TTR) type break down into two disease groups, namely a group with an abundance of different diseases that are inherited as an autosomal dominant trait and occur in younger years, and non-hereditary amyloidosis, which occurs sporadically, especially in old age and called old age amyloidosis.
Hereditary amyloidoses of this type are also known as familial amyloid polyneuropathies. They are caused by certain amino acid changes in transthyretin (TTR). The diagnosis is best made with a skin or sural biopsy, but also with a rectal biopsy. These diseases are primarily characterized by an ascending polyneuropathy, initially affecting the limbs with muscle weakness, then also the autonomic nervous system with signs of malabsorption. TTR, formerly known as prealbumin, is the thyroxine's transport protein. The most common mutation is the replacement of valine in position 30 with methionine. This mutation leads to familial amyloid polyneuropathy (FAP type I, Portuguese-Japanese type). Today over 50 different point mutations are known (1). Depending on the type of point mutation, cardiac or renal symptoms occur in addition to the polyneuropathy. Many of the polyneuropathies become manifest in the third to fifth decade and lead to death within about 10 years. Protein or genetic analyzes of transthyretin are essential for an exact diagnosis, which can also be made prenatally.The only therapy available today, orthotopic liver transplantation, is very successful because the liver is the main organ for the synthesis of amyloidogenic transthyretin (1, 8). More than 250 patients worldwide and around 15 patients in various centers in Germany (as of September 1998) have been liver transplanted. This therapy prevents the further progression of the disease and seems to lead to a very slow regression of the amyloid deposits over the years.
The common but little known old man amyloidosis (systemic senile amyloidosis) has its main manifestation site in the heart. Later on, the lungs, joints and many other organs are also affected by small deposits, which, however, cause little or no clinical symptoms. The transthyretin deposited here shows no point mutation. This form of age amyloidosis leads to impaired cardiac function. Digitalis toxicity separates this from other forms of age-related cardiomyopathies.
Amyloidoses of b2 microglobulin origin
Amyloidosis of b2-microglobulin origin is found in patients with uremia, kidney failure and dialysis treatment. The connective tissue of structures near the joints, mostly large joints, is affected, including the tendon sheaths (carpal tunnel syndrome) and the bone marrow. The latter lead to bone erosions (radiologically visible cystic lightening) with subsequent pathological bone fractures. The number of patients with b2m amyloid increases with the duration of dialysis treatment. After about 20 years of dialysis, most patients have developed this form of amyloidosis. The occurrence of this amyloidosis depends on age (younger age protects against early occurrence) and above all on the type of membrane used for dialysis (7). An early kidney transplant and the use of biocompatible dialysis filters prevent or delay the occurrence of this disease.
Other amyloid syndromes
In addition to the amyloid syndromes discussed above, other important amyloid syndromes should be mentioned here, some of which are of great clinical importance. However, no therapy is currently known.
In old-age diabetes (type II diabetes), an "island hyalinosis" is regularly found, and the amount correlates with the severity of the disease. This hyaline substance represents amyloid according to the criteria mentioned above. The material deposited as amyloid is formed in the B cells of the pancreas and secreted together with the insulin. It is referred to as the islet amyloid polypeptide (IAPP, Table 3) and can be detected in the paraffin tissue section with the aid of specific antibodies.
Alzheimer's diseases are characterized by plaque-shaped deposits that interrupt the synapses in the gray matter and, with increasing amounts, disrupt normal intellectual brain functions to such an extent that communication with the patient is hardly possible in the late stages. The so-called b protein is deposited in an amyloid conformation (Ab, Table 3). This disease is strictly age-dependent and can affect up to two percent of the population. Because of the increase in life expectancy, the prevalence of this disease will increase. In addition to the sporadic old-age disease, there are also hereditary forms that begin in the fourth and fifth decades and are inherited as an autosomal dominant trait (3). Deposits of the b-protein in the amyloid conformation also occur regularly in the leptomeningial vessels in Alzheimer's disease. These leptomeningial amyloid deposits occur in the brain even without amyloid plaques and are either symptom-free or also lead to senile dementia (3).
Transmissible cerebral amyloidoses are a number of diseases that can be transmitted to another individual and even to another species. These transmissible amyloidoses include spongiform encephalopathies such as Creutz-feldt-Jakob disease, Gerstmann-Strüßler-Scheinker disease and Kuru, a disease in the Papuans in New Guinea that was caused by ritual cannibalism. Similar diseases can also be found in animals, although scrapie in sheep and bovine cattle disease (BSE) have made various headlines over the past decade (14). The experimental and accidental transmissibility of these diseases from individual to individual has attracted particular public attention, the pathogenic agent, as far as we know, being a protein in the amyloid conformation (scrapie-associated or prion protein, AScr, Table 3).
Non-amyloid protein storage diseases
In addition to the amyloid deposits, protein deposits are also described which have no amyloid characteristics. In terms of light optics, these can look deceptively similar to the amyloids. Electron-optically one finds mainly unstructured protein deposits or fibrils, which hardly resemble the amyloid fibrils. These diseases are often confused with amyloidoses. Its course and its prognosis have not yet been clarified in detail. This is a relatively heterogeneous group of diseases, the deposited proteins of which have only been analyzed in a few cases. The most common deposits are of the immunoglobulin type, similar to Ig amyloids. Most of these deposits originate from k light chain aggregates. These diseases associated with nephropathy and restrictive cardiomyopathy, called LCDD (light chain deposition disease), require drastic chemotherapy, like that of AL amyloidoses.
How this article is cited:
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Address for the authors
Prof. Dr. med. Reinhold P. Linke
Max Planck Institute for Biochemistry
At the Klopferspitz 8a
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