Clinical History
This 75-year-old man with amyotrophic lateral sclerosis (ALS) for 5 years has a past medical history of gout and dysphagia. Upon physical exam, he showed slowly progressive weakness: Left>right, upper>lower extremity, distal>proximal, and grip strength 2/5 left, 4/5 right.
Question
What is the most likely diagnosis?
A. Denervation
B. Myotonic dystrophy
C. sIBM
D. Gouty tophus
Answer
The answer is C. sIBM.
Sporadic Inclusion Body Myositis (sIBM)
Resembles other idiopathic inflammatory myopathies. Rimmed vacuoles (inclusion bodies) may not be identified on H&E or trichrome.
- Immunohistochemistry: abnormal protein aggregates (e.g. TDP-43, p62, LC3B) in inclusions
- Granular dense material in vacuoles on Toluidine blue stained, plastic embedded, 1-micron-thick section
- Mitochondrial pathology: COX-/SDH+ (ragged-red equivalent) fibers in most cases
Treatment resistant, progressive, asymmetric distal weakness mimics ALS Finger flexor (grip strength) weakness is characteristic.
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