White Muscle Disease

Also known as Stiff lamb disease, characterised by myodegeneration. Disease is stress induced so the breakdown of muscle relies on increased muscle activity. Muscle degenerates due to a failure to control the free radicals produced by its metabolism upon contraction. Free radicals damage cellular membranes and proteins.

Muscle damage allows the release of:

Potassium: can lead to heart failure.
Myoglobin: can lead to renal failure.
Creatine Kinase: useful to measure muscle damage.

Grossly the damaged muscle will contain white streaks.

The damage caused by Zenker degeneration is reversible if the sarcolemma remains intact.

White muscle disease (Image sourced from Bristol Biomed Image Archive with permission)

Very important economic disease of sheep, cattle and pig
Caused by:
- Deficiency of selenium, vitamin E or both
- Exacerbated by rapid growth, unaccustomed exercise or other dietary factor
Pathogenesis:
- Oxygen free radicals (OFR) can damage cell membranes
- Vitamin E usually mops up OFRs
- Selenium as part of glutathione peroxidase neutralises effects of OFRs
- If Vit E or Se are deficient -> the balance shifts to membrane damage, calcium entry and mitochondrial damage -> cell swells and dies -> segmental muscle necrosis
Grossly:
- Lesions are bilaterally symmetrical in hard working muscles (vary with species)
- Early lesions are pale areas and streaks
  - Difficult to see especially in pale muscles
- Later becoming calcified necrotic areas
  - More obvious
- Pigs also have lesions in their heart and liver
Histologically:
- Segmental necrosis +/- calcification and regeneration
- Multifocal and multiphasic lesions