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Amyloidosis

Amyloidosis refers to the deposition of amyloid protein in organs and tissues. Primary amyloidosis is a plasma cell neoplasm that secretes an abnormal immunoglobulin. Amyloid protein is produced by the abnormal cleavage of immunoglobulin light chains and their aggregation into insoluble beta pleated sheets. Amyloid is deposited in various organs and tissues including tongue, intestines, skeletal and smooth muscles, nerves, skin, ligaments, heart, liver, spleen and kidneys. Most symptoms of amyloidosis are nonspecific. Weight loss is the most common, combined with weakness and fatigue. Dyspnea, edema and paresthesias are also common symptoms. Clinical presentations include:

• Nephrotic syndrome
• Infiltrative cardiomyopathy without ischemic history
• Hepatosplenomegaly with no filling defects visible by imaging
• Nondiabetic peripheral neuropathy
• Macroglossia
• Facial purpura

Amyloid occurs most frequently in individuals between the ages of 60 and 67 years. Only 1% of amyloidosis patients are under age 40. The male to female ratio is 2:1. Approximately 6% of patients with multiple myeloma develop amyloidosis.

No blood tests, radiographs or scans can diagnose amyloidosis. Biopsy is the gold standard for diagnosis. Any affected organ or tissue can be biopsied. Because amyloid proteins are carried throughout the bloodstream, any biopsy that includes blood vessels can be used to demonstrate the presence of amyloid. Rectal mucosa biopsies are noninvasive, easy to perform and have a low incidence of complications, but are not favored by many patients. Fat tissue is a common site of amyloid deposition. Aspiration of subcutaneous abdominal fat is a simple procedure with a low incidence of complications and high patient acceptance. It detects 70 to 80% of patients with amyloidosis. Congo red stain is diagnostic of amyloid fibrils, but must be performed by laboratories with extensive experience with this technique.

Bone marrow biopsy can also be used to detect amyloid deposition as well as clonal plasma cells. Sixty percent of patients with amyloidosis will have <10% plasma cells in the bone marrow and 20% of patients will have >20% plasma cells. Bone marrow biopsy combined with abdominal fat aspirate will detect 90% of patients with amyloidosis.

Serum protein electrophoresis will detect a monoclonal protein in approximately two thirds of patients with amyloidosis. Immunofixation is more sensitive and will detect a monoclonal protein in approximately 90% of patients.