Periodic Paralysis
Definition: Periodic paralyses are rare disorders characterized by episodic muscle weakness or paralysis caused by abnormalities of muscle membrane ion channels and electrolyte disturbances, while sensation and consciousness remain normal.
Classification
A. Hypokalemic Periodic Paralysis (Most Common)
Etiology: Autosomal dominant calcium/sodium channel mutations. May occur with thyrotoxicosis
Triggers: High-carbohydrate meals. Rest after exercise. Stress
Clinical Features: Episodic flaccid weakness. Proximal muscles affected more than distal. Legs > arms. Attacks last hours to days. Reflexes decreased during attack
Laboratory: ↓ Serum potassium during attack
Treatment: Potassium supplementation. Acetazolamide (prevention)
B. Hyperkalemic Periodic Paralysis
Etiology: Sodium channel mutation
Clinical Features: Short attacks (minutes–hours). Muscle stiffness (myotonia) may occur
Triggers: Rest after exercise. Fasting. Potassium-rich foods
Laboratory: ↑ Serum potassium during attack
Treatment: Carbohydrate intake. Avoid potassium excess
Diagnosis: Clinical history. Serum potassium during attacks. EMG. Genetic testing
Metabolic Myopathies
Definition: Inherited or acquired disorders affecting muscle energy metabolism.
Main Types
A. Glycogen Storage Diseases
McArdle Disease (Type V)
Defect: Myophosphorylase deficiency
Clinical Features: Exercise intolerance. Muscle cramps. Myoglobinuria after exercise
Characteristic Sign: Second-wind phenomenon.Symptoms improve after brief rest
B. Mitochondrial Myopathies
Clinical Features: Exercise intolerance. Muscle weakness. Fatigue
Associated Findings: Ophthalmoplegia. Ptosis. Cardiomyopathy
C. Lipid Metabolism Disorders
Features: Weakness during prolonged exercise or fasting. Recurrent rhabdomyolysis
Diagnosis: Elevated CK (variable). EMG: myopathic pattern. Muscle biopsy. Genetic testing