Amyloid Myopathy Masquerading as Polymyositis

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Amyloid Myopathy Masquerading as Polymyositis

LISA A. MANDL, REBECCA D. FOLKERTH, MICHAEL A. PICK,

MICHAEL E. WEINBLATT, and ELLEN M. GRAVALLESE

ABSTRACT.

Objective. It is not well appreciated that the clinical presentation of

amyloid myopathy can mimic that of polymyositis. By retrospective

clinicopathologic analysis we determined distinctive features of amyloid

myopathy that differentiate the 2 diseases.

Methods. Two patients with clinical and histologic evidence of an

inflammatory myopathy had fatal outcomes despite appropriate treatment

for polymyositis. Their clinical course and original pathologic

specimens were reviewed. In addition, original tissue samples were

obtained and analyzed using Congo red staining and immunoperoxidase.

Results. The initial diagnosis of polymyositis was supported in both

cases by muscle biopsies showing inflammatory infiltrates and elevations

of creatine phosphokinase and by classic electromyography. Retrospective

evaluation of the initial muscle biopsies disclosed subtle but

incontrovertible evidence of vascular amyloid. Further analysis of the

original specimens confirmed the presence of immunoglobin light chain

(AL) amyloid.

Conclusion. Amyloid myopathy can mimic polymyositis. Both can have

similar clinical symptoms, as well as inflammatory infiltrates on muscle

biopsy. Failure to recognize amyloid myopathy deprives patients of

potentially life prolonging treatment. Congo red staining and

immunohistochemical analysis of tissue could prevent misdiagnosis. (J

Rheumatol 2000;27:949–52)