Hypokalemic periodic paralysis

Background

• Autosomal dominant channelopathy
• Acquired hypokalemia from barium poisoning, hyperthyroidism, renal disorders, and GI losses
• Most first attacks happen by age 16
• Young males, Asian
• There is no decrease in total body potassium. Blood potassium level is normal between attacks.
• Associations
  • Thyrotoxicosis (thyrotoxicosis periodic paralysis)
  • Steroids
  • ETOH
  • Renal disease

Clinical Features

Symptoms

• Muscle weakness or paralysis with associated hypokalemia (though potassium levels can be normal)
• Sometimes painful though often painless
• Weakness can be from hand to leg to complete paralysis

History

• Strenuous exercise
• High carbohydrate meal
• High sodium meals
• Sudden changes in temperature
• Emotional stress
• Attacks can last several hours to several days

Physical Exam

• Reflexes are decreased or absent
• Shoulders and hips, are involved more often than the arms and legs.
• There is flaccid paralysis rather than hypertonia
• There should not be myoclonus or spasticity

Differential Diagnosis

Weakness

• Neuromuscular weakness
  • Upper motor neuron:
    • CVA
    • Hemorrhagic stroke
    • Multiple sclerosis
    • Amyotrophic Lateral Sclerosis (ALS) (upper and lower motor neuron)
  • Lower motor neuron:
    • Spinal and bulbar muscular atrophy (Kennedy's syndrome)
  • Spinal cord disease:
    • Infection (Epidural abscess)
    • Infarction/ischemia
    • Trauma (Spinal Cord Syndromes)
    • Inflammation (Transverse Myelitis)
      • Acute flaccid myelitis
    • Degenerative (Spinal muscular atrophy)
    • Tumor
  • Peripheral nerve disease:
    • Guillain-Barre syndrome
    • Toxins (Ciguatera)
    • Tick paralysis
    • Diabetic peripheral neuropathy
  • Neuromuscular junction disease:
    • Myasthenia gravis crisis
    • Botulism
    • Organophosphate toxicity
    • Lambert-Eaton myasthenic syndrome
  • Muscle disease:
    • Rhabdomyolysis
    • Dermatomyositis
    • Polymyositis
    • Alcoholic myopathy
• Non-neuromuscular weakness
  • Can't miss diagnoses:
    • ACS
    • Arrhythmia/Syncope
    • Severe infection/Sepsis
    • Hypoglycemia
    • Periodic paralysis (electrolyte disturbance, K, Mg, Ca)
      • Hypokalemic periodic paralysis
      • Thyrotoxic periodic paralysis
    • Respiratory failure
  • Emergent Diagnoses:
    • Symptomatic Anemia
    • Severe dehydration
    • Hypothyroidism
    • Polypharmacy
    • Malignancy
    • Aortic disease - occlusion, stenosis, dissection
  • Other causes of weakness and paralysis
    • Acute intermittent porphyria (ascending weakness)

Evaluation

Labs

• Chemistry (potassium)
• Magnesium
• TFTs for first presentation

ECG Findings

• Sinus bradycardia
• ECG signs of hypokalemia may be present but not always diagnostic
  • U waves in leads II, V-2, V-3, and V-4
  • Progressive flattening of T waves and depression of ST segment
  • Prolongation of the PR and QT intervals

Management

• Replace potassium appropriately - do not try to correct to normal level as once the muscles release potassium you will likely overcorrect
• Consider propranolol 3 mg/kg PO, expect to see rise in potassium within 2 hours
  • Only in hemodynamically stable patients without significant conduction block
  • Beta blockers particularly helpful in thyrotoxicosis variant
• Long Term Treatment:
  • Should be initiated by primary physician but often includes eating a low carbohydrate diet and avoiding alcohol
  • Medications to increase potassium: Acetazolamide, Spironolactone, Potassium tablets

Disposition

• Can be discharged from ED after potassium repletion and resolution of symptoms
• Consider admission if patient remains symptomatic

See Also

• Hypokalemia