Muscle Conditions with Myotonia or Myotonia-like Symptoms

Clinical and Electrical Myotonia

Conditions where both clinical symptoms of myotonia (delayed muscle relaxation after contraction) and electrical myotonia (diagnosed via EMG) are present:

• Dystrophic Muscle Conditions:
  • Myotonic Dystrophy Type 1 (DM1)
  • Myotonic Dystrophy Type 2 (DM2)
• Non-Dystrophic Muscle Conditions (Channelopathies):
  • Chloride Channel (CLCN1) Disorders:
    • Myotonia Congenita:
      • Thomsen Disease (AD)
      • Becker Disease (AR)
  • Sodium Channel (SCN4A) Disorders:
    • Paramyotonia Congenita
    • Hyperkalemic Periodic Paralysis with Myotonia
    • Myotonia Fluctuans
    • Myotonia Permanens
    • Acetazolamide-Responsive Myotonia

Electrical but Not Clinical Myotonia

Conditions where electrical myotonia is evident on EMG but without observable clinical symptoms:

• Myopathies:
  • Myotubular Myopathy
  • Centronuclear Myopathy
  • Acid Maltase Disease (GSD II, Pompe Disease)
• Other Conditions:
  • Rippling Muscle Disease
  • Hypothyroidism
  • Schwartz-Jampel Syndrome
  • Episodic Ataxia Type 1

Symptoms Mimicking Myotonia (No Clinical or Electrical Evidence of Myotonia)

Conditions with symptoms resembling myotonia but lacking clinical or electrical features:

• Neuromuscular and Systemic Disorders:
  • Stiff-Person Syndrome
  • Brody Disease
  • Isaacs’ Syndrome
• Periodic Paralysis Syndromes:
  • Hypokalemic Periodic Paralysis
  • Normokalemic Periodic Paralysis
• Calcium Channel (CACNA1S) Disorders:
  • Hypokalemic Periodic Paralysis

Medication-Induced Symptoms Mimicking Myotonia

• Drugs Implicated:
  • Colchicine
  • HMG-CoA Reductase Inhibitors (Statins)
  • Propranolol
  • Terbutaline
  • Penicillamine
  • Cyclosporine

Genetic Patterns and Inheritance:

• Autosomal Dominant (AD):
  • Thomsen Disease (Myotonia Congenita)
  • SCN4A Disorders (Paramyotonia Congenita, etc.)
  • Calcium Channel (CACNA1S) Disorders
• Autosomal Recessive (AR):
  • Becker Disease (Myotonia Congenita)