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.

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).