Clinical history
This 60-year-old patient presented with chronic ptosis and mild muscle weakness. CPK levels were within normal limits.
Based on Figures #1 – #4 which of the following is the best diagnosis?
A. Polymyositis
B. IBM
C. Mitochondrial myopathy
D. McArdle disease
Figure 1: This medium power image shows scattered muscle fibers with mild basophilic tinctoral quality.
Figure 2: A higher power image shows scattered muscle fibers with coarse bright magenta to bluish staining between the sarcomeres and in a subsarcolemmal distribution (ragged-red muscle fibers).
Figure 3: This medium power image shows frequent COX-negative myofibers (blue tinctoral quality with this dual stain preparation)
Figure 4: Electron microscopy shows frequent muscle fibers with mitochondrial abnormalities:
-enlarged
-spirally arranged critae
-paracrystalline inclusions (“parking lot inclusions”)
Correct answer: C. Mitochondrial myopathy
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