Familial Periodic Paralysis

Aka: Familial Periodic Paralysis, Hypokalemic Periodic Paralysis

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II. Epidemiology

  1. Prevalence: 1 in 100,000 (rare)
  2. Typical onset of symptoms before age 20 years
  3. More common in males

III. Causes

  1. Genetic
    1. Autosomal Dominant disorder of Hypokalemia
    2. Most often related to a Sodium channel disorder, with a shifting of Potassium into tissues
  2. Acquired
    1. Hyperthyroidism

IV. Risk Factors: Triggers

  1. Alcohol Abuse
  2. Corticosteroid use
  3. Insulin
  4. Renal disease
  5. Large Carbohydrate containing meals
  6. High salt intake
  7. Intense Exercise
  8. Glue sniffing
  9. Prolonged immobility
  10. Cold Weather
  11. Anesthetics

V. Symptoms

  1. Headaches
  2. Thirst
  3. Lethargy
  4. Generalized Muscle Weakness
  5. No associated pain

VI. Signs

  1. Slow progressive weakness (especially following triggers)
    1. Weakness lasts for hours to days
  2. Episodic muscular paralysis (lower extremities > upper extremities)
    1. Shoulder
    2. Pelvic girdle
    3. Other areas follow
  3. Muscle Strength normal between attacks
  4. Deep Tendon Reflexes
    1. Diminished or absent

VII. Associated Conditions

  1. Thyrotoxicosis
    1. Especially in young asian males, with onset after Exercise

VIII. Labs

  1. Consider extending evaluation to cover differential diagnosis as below
  2. Serum Electrolytes including Renal Function and Magnesium
    1. Serum Potassium with Hypokalemia during episode (normal between episodes)
    2. Hypomagnesemia may be associated with other causes of Hypokalemia
  3. Thyroid Stimulating Hormone (TSH)
    1. Evaluate for Thyrotoxicosis
  4. Genetic Testing
    1. Genetic outpatient testing if findings consistent with familial Hypokalemia

IX. Diagnostics

  1. Electrocardiogram
    1. See Hypokalemia for related EKG changes

X. Differential Diagnosis

  1. See Hypokalemia Causes
  2. See Acute Motor Weakness Causes

XI. Management

  1. Replace Potassium IV in severe cases (oral Potassium in mild cases)
    1. See Potassium Replacement
    2. Exercise caution with replacement
      1. Risk of overshooting as Muscles release Potassium on recovery
  2. Replace Magnesium if low
  3. Avoid high Carbohydrate intake
  4. Avoid Excessive Salt Intake

XII. Complications

  1. Myopathy

XIII. Prevention

  1. Carbonic anhydrase inhibitors (e.g. Acetazolamide)
  2. Potassium sparing Diuretics (e.g. Spironolactone)

XIV. References

  1. Candy and Herbert in Herbert (2020) EM:Rap 20(11): 8-9
  2. Claudius and Behar in Herbert (2019) EM:Rap 19(11):12-3

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