What is the role of muscle biopsy in the workup of polymyositis?

Updated: Feb 12, 2018
  • Author: Mythili Seetharaman, MD; Chief Editor: Herbert S Diamond, MD  more...
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Answer

Muscle biopsy (eg, deltoid or quadriceps femoris) is crucial in helping to diagnose polymyositis and in excluding other rare muscle diseases. [23] MRI and EMG can be used to guide the site of biopsy. Avoid biopsy of sites recently studied with EMG by using the contralateral side.

Inflammatory changes are seen on muscle biopsy. Findings occasionally may be normal because of patchy involvement. (See the images below.)

Hematoxylin and eosin frozen section shows polymyo Hematoxylin and eosin frozen section shows polymyositis. Endomysial chronic inflammation is present among intact myofibers, which are remarkable only for increased variability of fiber size. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polym Hematoxylin and eosin paraffin section shows polymyositis. Patient had dense endomysial inflammation that contains an abundance of plasma cells, which can be observed in patients with chronic polymyositis. Two necrotic myofibers, characterized by dense eosinophilic staining, are observed. Focal fatty infiltration of the muscle is present in the lower left quadrant of the photomicrograph. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polym Hematoxylin and eosin paraffin section shows polymyositis. Photomicrograph illustrates attack on a nonnecrotic myofiber by autoaggressive T lymphocytes. On the left, the central myofiber is intact. On the right, it is obliterated by a segmental inflammatory attack. If immunohistochemistry were performed, expected findings would include an admixture of CD8 T lymphocytes and macrophages in the inflammatory process. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polym Hematoxylin and eosin paraffin section shows polymyositis. Longitudinal section shows a dense, chronic, endomysial inflammatory infiltrate. Image courtesy of Roberta J. Seidman, MD.

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