Amyloidosis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
In medicine, amyloidosis refers to a variety of conditions in which amyloid proteins are abnormally deposited in organs and/or tissues, causing disease. A protein is amyloid if, due to an alteration in its secondary structure, it takes on a particular insoluble form, called the beta-pleated sheet. Approximately 25 different proteins are known that can form amyloid in humans. Most of them are constituents of the plasma.Different amyloidoses can be systemic (affecting many different organ systems) or organ-specific. Some are inherited, due to mutations in the precursor protein. Other, secondary forms are due to different diseases causing overabundant or abnormal protein production-such as with over production of immunoglobulin light chains in multiple myeloma (termed AL amyloid), or with continuous overproduction of acute phase proteins in chronic inflammation (which can lead to AA amyloid).
Classification
The more common types of amyloid include AL, AA, Aβ, ATTR and Aβ2M from the 15 biologically distinct forms.
Pathophysiology
Amyloid is a pathological extracellular deposit composed predominantly of amyloid fibrils. Amyloidosis is disease caused by amyloid deposits in the tissues. The deposits may be local or systemic in distribution and acquired or hereditary in aetiology. All patients with amyloidosis have amyloid deposits in their tissues when they first present clinically. Clinical impairment progresses as amyloid deposits increase in size, and regression of amyloid is associated with clinical improvement and survival. Secondary amyloidoses is far more common than the primary amyloidoses.
Causes
Amyloidosis is can be systemic or organ specific. In systemic amyloidosis, secondary variety (AL, AA) is far more common than the primary one.
Differentiating Amyloidosis from other diseases
Amyloidosis needs to be differentiated from acute myocarditis, bronchiectasis, multiple myeloma and other systemic diseases .
Risk Factors
Risk factors have not been identified.
Natural History, Complications and Prognosis
The complications of amyloidosis include hyposplenism, malabsorbtion syndrome, myopathy, proximal renal tubular acidosis and renal failure. The severity the disease depends on the organs that are affected. When the heart and kidney are involved, it may lead to organ failure and death.
Diagnosis
History and Symptoms
Symptoms depend on the organs affected by the deposits. These organs can include the tongue, intestines, skeletal and smooth muscles, nerves, skin, ligaments, heart, liver, spleen, and kidneys.
Physical Examination
Common findings in amyloidosis include petechiae, ecchymosis, parotid gland enlargement, increased intra ocular pressure, enlarged tongue, hepatomegaly, carpal tunnel syndrome and Raynaud phenomenon.
Laboratory Findings
Laboratory findings in amyloidosis include elevated erythrocyte sedimentation rate, increased BUN level, serum creatinine, protein, casts, or fat bodies in urine. Serum troponin, B-type natriuretic peptide, and beta-2-microglobulin are prognostic markers for heart failure. Amyloid deposits can be identified histologically by Congo red staining and viewing under polarized light where amyloid deposits produce a distinctive 'apple green birefringence'. Alternatively, thioflavin T stain may be used. An abdominal fat pad aspiration, rectal mucosa biopsy, or bone marrow biopsy can help confirm the diagnosis. They reveal positive findings in 80% patients.
Electrocardiogram
EKG findings in a case of amyloidosis include an abnormal rhythm and low voltage recordings.
Chest X Ray
The X ray findings in a case of amyloidosis include a coin lesion.
MRI
Cardiac MRI is used when echocardiogram fails to differentiate amyloidosis from hypertrophic cardiomyopathy.
Echocardiography
Echocardiography is useful to evaluate extent of heart involvement. The common findings include thickened ventricular wall and wall motion abnormalities.
Other Imaging Findings
Tissue Doppler and myocardial strain rate imaging has been proven to be very sensitive for the assessment of myocardial dysfunction in restrictive cardiomyopathy. Serum amyloid P component (SAP) scans have been developed which can anatomically localize amyloid deposits.
Treatment
There is no treatment for primary amyloidosis. The initial target in the treatment of this disorder is to correct the organ failure, as the disease is discovered at an advanced stage.