Periodic Paralysis

Basics

Description

  • Periodic paralysis (PP): Disorder of muscle metabolism, usually inherited, that leads to flaccid extremity weakness
  • Primary: Familial autosomal dominate (AD) mutation in skeletal muscle calcium, sodium, or potassium channels
  • Secondary: Due to thyrotoxicosis, hypokalemia, or hyperkalemia

Epidemiology

Incidence and Prevalence Estimates
  • Hypokalemic PP (HypoPP):
    • Prevalence: 1:100,000
    • 1/3 are new AD mutations
  • Hyperkalemic PP (HyperPP):
    • Prevalence: 1:200,000
    • 90% of people with mutation will have clinical symptoms
  • Thyrotoxic PP (ThyroPP):
    • Incidence: 2% in patients with thyrotoxicosis
    • Higher in Asians
    • Subset of HypoPP, clinically identical
  • Andersen–Tawil:
    • Subset of HypoPP
    • Rare
    • Prevalence unknown

Etiology

  • Mutation of skeletal muscle Na channel gene:
    • SCN4A
    • HypoPP, HyperPP:
      • AD inheritance
      • Spontaneous mutation
  • Mutation of skeletal muscle calcium channel gene CACN1AS:
    • HypoPP
  • Mutation of KCNJ2 gene:
    • Andersen–Tawil:
      • AD inheritance
      • 50% spontaneous
  • M > F
  • Age of onset:
    • HypoPP:
      • First or second decade
    • HyperPP:
      • First decade
    • Andersen–Tawil:
      • First or second decade
    • ThyroPP:
      • Second–fifth decade

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