What are the causes of Non-Convulsive Status Epilepticus (NCSE)?

Causes of Non-Convulsive Status Epilepticus (NCSE)

Non-convulsive status epilepticus (NCSE) is primarily caused by central nervous system infections, metabolic derangements, toxic exposures, cerebrovascular events, and pre-existing epilepsy, with infectious encephalitis affecting the cortex being a particularly significant etiology. 1

Primary Etiological Categories

Infectious Causes

• Viral encephalitis: Particularly HSV and Japanese encephalitis virus 1
• Bacterial infections:
  • Septic encephalopathy (found in 50-70% of septic patients) 1
  • Urinary tract infections (especially in pediatric patients) 1
  • Shigella and typhoid fever 1

Cerebrovascular Events

• Stroke (both acute and remote) 1
• Hypoxic-ischemic encephalopathy 2, 3
• Vascular events associated with VZV infection 1

Metabolic/Toxic Causes

• Electrolyte abnormalities (particularly hyponatremia) 1, 4
• Drug toxicity or withdrawal 1, 5
• Medication effects (especially psychotropic drugs in elderly patients) 6

Structural Brain Lesions

• Tumors 1
• Traumatic brain injury 1, 6

Pre-existing Neurological Conditions

• Chronic epilepsy 1
• Autoimmune disorders (including autoimmune encephalitis) 3, 6

Clinical Presentation Patterns

NCSE presents differently based on the underlying type:

1. Generalized NCSE (Absence Status Epilepticus):

   • Occurs in idiopathic generalized epilepsy (typical absence status)
   • Symptomatic generalized epilepsy (atypical absence status)
   • De novo absence status in elderly patients on psychotropic medications 6

2. Complex Partial Status Epilepticus:

   • Temporal lobe origin
   • Extratemporal cases (including frontal lobe types I and II) 6

3. Simple Partial Status Epilepticus:

   • Often underdiagnosed due to subtle symptoms and frequent progression to complex partial status 6

Diagnostic Challenges

NCSE is frequently overlooked because:

• Symptoms are non-specific (altered mental status, behavioral changes) 1
• No overt motor seizure activity is present 1
• It can only be definitively diagnosed with EEG 1
• It may be masked by underlying critical illness 4

High-Risk Populations

• Elderly patients: Particularly those on psychotropic medications 6
• ICU patients: 8% of comatose ICU patients may have unrecognized NCSE 1
• Post-convulsive seizure patients: NCSE may follow overt convulsive seizures or status epilepticus 1
• Patients with encephalopathy: Any unexplained altered mental status should prompt consideration of NCSE 1, 4

Clinical Pearls and Pitfalls

• Key pitfall: Failure to consider NCSE in patients with altered mental status without obvious seizure activity 7
• Diagnostic gold standard: EEG is essential and should be performed urgently in suspected cases 2
• Treatment impact: NCSE is potentially reversible with appropriate anticonvulsant therapy 4
• Prognostic factors: Outcomes are worse when NCSE is caused by toxic/metabolic derangements or anoxia compared to chronic epilepsy, infections, tumors, stroke, or trauma 1

Management Considerations

When NCSE is suspected:

1. Obtain urgent EEG (continuous monitoring preferred) 2
2. Administer benzodiazepines as first-line treatment 2, 7
3. Consider second-line antiepileptic drugs (levetiracetam, valproate) if seizures persist 2
4. Treat the underlying cause when identified 3

Early recognition and treatment of NCSE is critical as prolonged NCSE (>36 hours) is associated with significant morbidity and mortality, particularly in comatose patients with hypoxic-ischemic encephalopathy 2, 3.