Felis ISSN 2398-2950

Myotonia congenita

Synonym(s): Congenital myotonia

Contributor(s): Laurent Garosi

Introduction

  • Cause: skeletal muscle channelopathy, mutation in skeletal muscle chloride channel (CLCN1) identified in some cats.
  • Signs: inability of the muscle to relax following voluntary contraction resulting in stiffness and temporary inability to initiate movement, hypertrophy proximal appendicular muscles.
  • Diagnosis: clinical signs, typical myotonic discharges on EMG and histopathologic and histochemical findings in muscle.
  • Treatment: procainamide, quinidine, phenytoin and mexiletine.
  • Prognosis: guarded despite medication.

Pathogenesis

Etiology

  • Skeletal muscle channelopathy.
  • Block in chloride conductance in the muscle fiber membrane.
  • Mutation in skeletal muscle chloride channel (CLCN1) identified in some cats.

Predisposing factors

General

  • None identified.

Specific

  • Mutation in skeletal muscle chloride channel (CLCN1) identified in some cats.

Pathophysiology

  • Diminished chloride conductance across the muscle membrane which compromises the resting membrane potential.
  • As the chloride channel contributes approximately two-thirds of the resting membrane conductance, a decrease in chloride channel conductance significantly compromises the resting membrane potential.
  • During normal muscle activation-depolarization, potassium ions accumulate in the sarcoplasmic reticulum and increase the probability of further depolarizations which is ‘buffered’ in the presence of normal high chloride conductance.
  • Loss of conductance tips the balance towards potassium-induced depolarization burst that manifest as myotonia.
  • Genetic defects in the skeletal muscle ion channels in some cases (mutation in skeletal muscle chloride channel (CLCN1) identified in some cats).

Timecourse

  • Tend to be static.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Gandolfi B, Daniel R J, O’Brien D P et al (2014) A novel mutation in CLCN1 associated with feline myotonia congenital. PLoS One (10), e109926 PubMed.
  • Gaschen F, Jaggy A, Jones B (2004) Congenital diseases of feline muscle and neuromuscular junctionJ Feline Med Surg (6), 355-366 PubMed.
  • Vite C H (2002) Myotonia and disorders of altered muscle cell membrane excitability. Vet Clin North Am Small Anim Pract 32 (1), 169-187 PubMed.
  • Hickford F H, Jones B R, Gething M A et al (1998) Congenital myotonia in related kittens. J Small Anim Pract 39 (6), 281-285 PubMed.
  • Toll J, Cooper B (1998) Feline congenital myotonia. J Small Anim Pract 39 (10), 499 PubMed.
  • Toll J, Cooper B, Altschul M (1998) Congenital myotonia in 2 domestic cats. J Vet Intern Med 12 (2), 116-119 PubMed.


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