Periodic Paralysis

Basics

Description

Periodic paralysis (PP): Rare group of skeletal muscle channelopathies characterized by episodic extremity muscle weakness/flaccidity:

  • Primary: Familial autosomal dominant (AD) mutation in skeletal muscle calcium, sodium, or potassium channels
  • Secondary: Due to thyrotoxicosis, toxic substances, or electrolyte disturbances, particularly hypokalemia or hyperkalemia

Epidemiology

Incidence And Prevalence Estimates

  • Hypokalemic PP (HypoPP):
    • Prevalence: 1–1.5:100,000
    • 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):
    • Well-documented in Asian populations
    • Incidence: 1.8–1.9% in Chinese and Japanese; 0.1–0.2% North American patients with thyrotoxicosis
    • Subset of HypoPP, clinically identical
  • Andersen–Tawil syndrome (ATS):
    • Subset of HypoPP, characterized by triad of PP, cardiac abnormalities (ventricular arrhythmia with prolonged QT and prominent U wave), and skeletal dysmorphism
    • Rare
    • Prevalence: 1:1,000,000

Etiology

  • AD inheritance
  • Spontaneous mutation
  • Sex: M > F
  • HypoPP:
    • Most caused by mutation in Cav1.1 gene, CACN1AS or Nav1.2 gene, SCN4A
    • Age of onset: 1st–2nd decade
  • HyperPP:
    • Most commonly caused by mutation Nav1.2 gene, SCN4A
    • Age of onset: 1st decade
  • ThyroPP:
    • Hyperthyroidism, most commonly caused by Grave disease
    • Age of onset: 2nd–5th decade
  • ATS:
    • Most commonly caused by mutation in Kir2.1 gene KCNJ2
    • AD inheritance
    • 30% spontaneous
    • Age of onset: 1st–2nd decade

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