Myotonia
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Myotonia
- Myotonia is the term given to sustained muscle contraction.
- Myotonia may be congenital or acquired.
Congenital
- Myotonia congenita is caused by an ion channel defect.
- Certain breeds of dogs are predisposed to myotonia congenita.
- Chow chow
- The condition is caused by a defect in the sodium channel.
- Schnauzer
- The condition is caused by a defect in the chloride channel.
- Chow chow
Clinical Signs
- Stiffness is present from birth.
- Signs improve with exercise.
- Hypertrophy of the tongue and appendicular muscles.
- Percussion dimple formation
- Biopsy results may:
- Be normal, or
- Show type 1 fibre predominance or hypertrophy.
Treatment
- Exercise avoidance.
- Drugs:
- Metilxantine
- Procainamide
Acquired
- Acquired myotonia may be caused by:
- Herbicides
- For example, (2,4-D) and dicamba.
- Hyperadrenocorticoidism
- This may be natural (i.e. increased endogenous steroid production), or iatrogenic (i.e. prolonged corticosteroid administration).
- Herbicides