Seizure Disorders - Epilepsy

Seizure disorders (epilepsy) can occur at any age and are associated with multiple etiologies.

Epidemiology

• Prevalence – 0.5-1% in most countries
• Gender – equal distribution

Classification

• Partial onset seizures
  • Simple
  • Complex
• Primary generalized seizures
  • Absence (petit mal)
  • Tonic-clonic (grand mal)
  • Tonic
  • Atonic
  • Myoclonic
• Nonclassified
  • Neonatal
  • Infantile spasms

Etiology

• Trauma
• Hypoxia
• Cerebrovascular disease
• Fever (only in children)
• Metabolic derangement
• Drug withdrawal
• Central nervous system infection
• Tumor
• Genetic disorders
• Idiopathic

Clinical Presentation

• Tonic-clonic seizure activity – contraction of all muscles with loss of consciousness
• Partial seizures – motor, sensory, autonomic impairment with preserved consciousness
• Absence seizures – loss of consciousness, but not postural control

Diagnosis

• Clinical history of seizures
• Electroencephalogram
  • May require continuous monitoring to identify seizure activity
• Brain imaging

Differential Diagnosis

• Central nervous system infection
• Metabolic disorders
• Migraine aura
• Psychogenic seizures
• Substance intoxication
• Syncope
• Transient ischemic attack or stroke

Treatment

• Treat underlying cause, if present
• Antiepileptic drugs are usually required in chronic disease

Monitoring

• Serial serum drug levels are important for dose optimization of anti-seizure drugs because of variable pharmacokinetics, drug-drug interactions, non-compliance and a narrow therapeutic index of most drugs
• Drug concentrations should be measured when signs of adverse effects or therapeutic failure are evident
• Drug-drug interactions are very common; many anti-seizure medications affect the metabolism of and compete for protein binding with other drugs.  As such, drug concentrations should be measured after any changes to drug regime
• Pharmacokinetics varies widely, particularly with co-medications and/or compromised renal function
• Serum drug concentrations are best interpreted when pre-dose (trough) specimens are collected after steady-state is achieved
• Serum drug concentrations change dramatically during pregnancy and may have important clinical and teratogenic consequences
• Free drug concentrations are important to consider for patients with abnormal or unpredictable protein status, when drugs that exhibit >90% protein binding are employed
• Recommended drug concentration monitoring (when steady state achieved)
  • Measurements: 
    • Baseline after starting drug therapy
    • After change in dosing
    • After adding a second antiepileptic drug or other new drug that may interfere with metabolism
    • After a change in patient’s liver, cardiac or gastrointestinal function

Indications for Ordering

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory