Muscle pathology and diseases are a high-yield topic for neurology examinations as many of these disorders have characteristic or pathognomonic findings that allow for easy test question writing! For this topic, pathology slide interpretation will be a great skill to have! Luckily this chapter has dozens of high-quality images with which to practice.
Author: Brian Hanrahan MD
Acquired Myopathies
TIP
The most important topics to know are muscle pathology identification, genetics, and which channels are involved with the channelopathies.
Idiopathic inflammatory myopathies
Polymyositis
- A female-predominant disease seen in one’s adult years that presents with subacute symmetric proximal weakness and pain.
- Can be associated with rheumatoid arthritis, HIV, or underlying malignancy.
- Muscle biopsy shows endomysial and perivascular monocytic inflammation and necrosis with regeneration.
Polymyositis
Note the inflammatory cells in the endomysium.
Polymyositis
Muscle biopsy with inflammatory cells in the endomysium (between and around individual myofibers) consistent with polymyositis.
Dermatomyositis
- A female-predominant disease which presents with subacute proximal weakness and pain.
- Dermatologic manifestations include a heliotrope rash on eyelids and an erythematous rash of the face or neck.
- Can be associated with connective tissue disease, malignancy, and interstitial lung disease.
- Muscle biopsy shows perifascicular inflammation and atrophy with sparing of the central fascicle.
Dermatomyositis
Note perimysial inflammation and atrophy.
Dermatomyositis
Trichrome stain with perifascicular atrophy.
Dermatomyositis
ATPase stain with perifascicular atrophy.
Inclusion body myositis (IBM)
A male-predominant slowly progressive idiopathic inflammatory condition of patients over the age of 50.
Clinical features include asymmetric weakness of the finger flexors and the quadriceps muscles.
Inclusion Body Myositis
Note the rimmed vacuoles (arrow).
Inclusion Body Myositis
Note the rimmed vacuoles (arrow).
Inclusion Body Myositis
Note the lymphocyte invasion.
Treatment
- Polymyositis and dermatomyositis are responsive to immunosuppressive therapies (steroids, methotrexate, azathioprine, mycophenolate, etc.) while IBM is not.
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