Non-convulsive status epilepticus (NCSE) is prolonged or repeated epileptic seizure activity in which the dominant clinical picture is not ongoing major convulsions. A person may instead show altered consciousness, confusion, reduced responsiveness, behavioural change or very subtle motor signs.
Why NCSE is difficult to recognise
Without continuous jerking or stiffening, NCSE can resemble delirium, sedation, metabolic encephalopathy, psychiatric illness, postictal confusion, dementia or other neurological disorders.
Some people are awake but unusually confused; others are drowsy, unresponsive or comatose. Small facial, eye or limb movements may occur, but they may also be absent.
EEG is central to diagnosis
Diagnosis usually depends on electroencephalography because the seizure activity may have little or no visible clinical expression.
The Salzburg EEG criteria and the American Clinical Neurophysiology Society critical-care EEG terminology provide structured ways to interpret electrographic patterns, but no EEG rule should be used without clinical context.
The Salzburg criteria are useful, not infallible
Prospective validation studies show that the Salzburg criteria can perform well, but false positives and borderline cases occur, particularly when rhythmic or periodic patterns lie close to the ictal-interictal boundary.
This is why the final diagnosis integrates EEG, clinical state, evolution over time, response to treatment and the underlying illness.
NCSE after a convulsive seizure
A person may stop convulsing but remain in electrographic status epilepticus. Failure to recover consciousness as expected after a convulsive seizure is therefore one important reason to consider urgent EEG monitoring.
This is particularly relevant in intensive care, where sedatives, brain injury and systemic illness can make clinical observation unreliable.
NCSE in people with and without epilepsy
NCSE can occur in people with established epilepsy, but it can also arise during acute brain injury, stroke, infection, autoimmune encephalitis, metabolic disturbance, drug toxicity or withdrawal and after cardiac arrest.
The underlying cause has a major effect on prognosis.
Treatment depends on context
NCSE is not one uniform condition. Treatment urgency and aggressiveness depend on the electroclinical pattern, seizure burden, level of consciousness, cause and risk from both ongoing seizures and treatment.
A comatose patient with electrographic status after an acute brain injury is different from a person with a prolonged absence-status presentation who remains relatively stable.
Why the ictal-interictal continuum matters
Some ICU EEG patterns are more abnormal than ordinary interictal discharges but do not satisfy definite seizure criteria. These are often described as lying on the ictal-interictal continuum.
The decision to treat such patterns is one of the most difficult areas in modern neurocritical care.
Related reading
Sources and further reading
- Sensitivity and specificity of the Salzburg EEG criteria for NCSE — 2024
- Diagnosing NCSE using EEG and antiseizure medication response
- Diagnosis, treatment and outcome prediction of NCSE in unconscious ICU patients
Evidence checked: September 2026.