Nov. 06, 2022
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Symptoms of primary systemic amyloidosis include neuropathy, myopathy, and cardiac or renal insufficiency; multiple organ systems are often involved. Amyloidosis can involve both the central nervous system and peripheral nerves. Amyloid myopathy is a rare manifestation of primary systemic amyloidosis. It is less well recognized that amyloid can directly infiltrate and weaken skeletal muscle. Like most other myopathies associated with systemic disorders, it is manifest by proximal limb muscle weakness and increased serum levels of creatine kinase.
• Amyloid myopathy is one of the uncommon manifestations of systemic amyloidosis.
• The symptoms are usually nonspecific, typically including progressive proximal limb weakness with an increased creatine kinase level, macroglossia, and muscle pseudohypertrophy.
• The diagnosis of amyloid myopathy is usually overlooked, and it is often misdiagnosed as inflammatory myopathy, even when a muscle biopsy is available.
• Amyloid myopathy associated with a plasma cell dyscrasia is a rare cause of muscle hypertrophy. It can be a challenging diagnosis because pathological findings are often elusive.
• When suspecting amyloid myopathy, Congo red staining and either an immunohistochemical assay or immunofluorescence study should be performed.
• Amyloid myopathy should be a consideration in adults with progressive neuromuscular weakness of uncertain cause.
• Recognition of amyloid myopathy is important because clinical symptoms may respond to melphalan and prednisone therapy
The first recognized patient with amyloid-associated muscle involvement was reported by Lubarsch in 1929; both vascular and interstitial deposits were seen in skeletal muscle and heart (25). It has now been reported in three of the largest series that myopathy is rarely caused by amyloidosis (13; 36; 48). Classification of the amyloidosis is based in part on the chemistry of the amyloid fibrils. Amyloidosis accompanying plasma cell dyscrasia is characterized by fibrils containing a component of immunoglobulin light chains. The oval masses may contribute to the muscular hypertrophy and to the formation of nodules within the muscles. These nodules may also contribute to muscle weakness by compression of nearby muscle fibers (06).
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