Amyloid myopathy

Jasvinder Chawla MD MBA (Dr. Chawla of Loyola University Medical Center and Chief of Neurology at Hines VA Hospital has no relevant financial relationships to disclose.)
Michio Hirano MD, editor. (Dr. Hirano of Columbia University has no relevant financial relationships to disclose.)
Originally released October 27, 2011; last updated on August 24, 2014; expires August 24, 2017

This article includes discussion of amyloid myopathy and muscle disease. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

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.

Key points

 

• 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

Historical note and terminology

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 (Lubarsch 1929). It has now been reported in 3 of the largest series that myopathy is rarely caused by amyloidosis (Gertz and Kyle 1996; Prayson 1998; Spuler et al 1998). 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 (Cohen and Rubinow 1984).

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