Clinical History:
This 17-year-old elite endurance athlete underwent muscle biopsy to evaluate for recent inability to perform at the level they could six-months ago.
In the context of this individual’s clinical history what is the best explanation for the changes seen on light and electron microscopy?
A. Inclusion Body Myositis
B. Vacuolar Myopathy
C. Polymyositis
D. Athletic Conditioning
Answer:
D. Athletic Conditioning
An increase in architecturally normal appearing mitochondria is commonly seen in elite endurance sport athletes. The increase in mitochondrial staining is best seen on modified Gomori Trichrome-stained sections on light microscopy and is less visible on hematoxylin and eosin-stained sections. Increased numbers of architecturally normal appearing mitochondria are present on electron microscopy.
Although increased mitochondria may be seen in the setting of Inclusion Body Myositis, no inflammation or rimmed-vacuoles characteristic of this disorder are seen, and this patient is too young for the disease.
No sarcoplasmic vacuoles are seen to suggest the presence of a vacuolar myopathy, as may be seen in toxic myopathy (for example colchicine and hydroxychloroquine) or acid maltase deficiency (Pompe disease).
No inflammation is seen to suggest the presence of polymyositis.
Reference(s) / Additional Reading:
- Lundby C, Jacobs RA. Adaptations of skeletal muscle mitochondria to exercise training. Exp Physiol. 2016;101(1):17-22. doi:10.1113/EP085319
- Grobler LA, Collins M, Lambert MI, et al. Skeletal muscle pathology in endurance athletes with acquired training intolerance. Br J Sports Med. 2004;38(6):697-
- Lewis NA, Collins D, Pedlar CR, Rogers JP. Can clinicians and scientists explain and prevent unexplained underperformance syndrome in elite athletes: an interdisciplinary perspective and 2016 update. BMJ Open Sport Exerc Med. 2015;1(1):e000063. Published 2015 Nov 25. doi:10.1136/bmjsem-2015-000063703. doi:10.1136/bjsm.2003.006502
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