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Amyloid myopathy: an underdiagnosed entity

S Spuler1, A Emslie-Smith, A G Engel

  • 1Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA.

Annals of Neurology
|June 18, 1998
PubMed
Summary

Amyloidosis rarely causes muscle weakness (myopathy). This study found amyloid deposits in muscle biopsies of 13 adults, increasing diagnosis rates with improved staining techniques.

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Area of Science:

  • Neurology
  • Pathology
  • Rheumatology

Background:

  • Systemic amyloidosis commonly affects organs like kidneys and heart, but skeletal muscle involvement as a primary myopathy is rare.
  • Muscle weakness can be an overlooked symptom of systemic amyloidosis, often diagnosed late or incidentally.
  • Previous diagnostic approaches may have underestimated the prevalence of amyloid myopathy.

Purpose of the Study:

  • To investigate the presentation and diagnosis of amyloidosis in patients with unexplained muscle weakness.
  • To identify the types of amyloidosis affecting skeletal muscle.
  • To evaluate the utility of specific staining techniques in diagnosing amyloid myopathy.

Main Methods:

  • Studied 13 adult patients with subacute to chronic muscle weakness.
  • Examined muscle biopsy specimens for congophilic deposits, fiber changes (necrosis, regeneration), and denervation signs.
  • Utilized immunostains to identify amyloid types (immunoglobulin, gelsolin) and co-localization of Apolipoprotein E and beta-amyloid precursor protein.
  • Compared diagnostic yield before and after implementing routine fluorescent Congo red staining.

Main Results:

  • All 13 patients showed congophilic deposits in muscle around blood vessels and fibers, with some necrotic/regenerating fibers and mild denervation.
  • Immunostains revealed immunoglobulin amyloidosis in 7 patients and gelsolin amyloidosis in 1.
  • Apolipoprotein E was found with deposits in all 10 tested patients; beta-amyloid precursor protein epitope in 6.
  • Adopting fluorescent Congo red staining increased the diagnosis frequency of amyloid myopathy tenfold.

Conclusions:

  • Amyloid myopathy is an underdiagnosed cause of muscle weakness.
  • Congophilic deposits in muscle biopsy are key indicators of amyloidosis.
  • Enhanced staining methods, particularly fluorescent Congo red, significantly improve the detection rate of amyloid myopathy.

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