Nonconvulsive Status Epilepticus

I recently wrote about a case of status epilepticus in a child. In that case the child stopped having tonic clonic seizures. However it appeared that there was ongoing nonconvulsive seizing. This was mostly diagnosed by fine tremors of the arms and divergent pupillary gaze.

This is a summary of a recent review article on nonconvulsive status epilepticus (NCSE) for emergency physicians(1).

NCSE is a difficult diagnosis to make. There is no consensus agreement on diagnostic criteria, or management. It may be that an electroencephalogram (EEG), is a main way to make the diagnosis. However this is not 100% specific and rarely available in the emergency department.

What we know is that NCSE is associated with an overall poor prognosis, with the most important determinant of mortality and morbidity being the cause of the seizure. The longer the duration of NCSE, the greater the mortality. This is not related to respiratory failure or lactic acidosis or rhabdomyolysis as occurs in convulsive status, but more due to sustained neuronal excitation.

NCSE can occur with coma, however it can also occur without coma, such as in absence seizures.

The challenge that we have is that the presentation may be subtle.

Aetiology of NCSE

• Epilepsy: In up to 50% of cases
  • Untreated or
  • Subtherapeutic levels of seizure medications.
• Acute Brain Injury
  • Intracerebral bleeds including Subarachnoid Haemorrhage
  • Ischaemic Stroke
• Infections
  • Encephalitis
  • Sepsis
• Medication related
• Toxic Ingestions

Clinical Presentation

The signs can be very subtle, leading to delay in diagnosis. The most common presentations are:

• Altered Mental Status (82%)
• Speech Disturbance (15%)
• Myoclonus (13%)
• Behavioural changes (11%)
• Anxiety, agitation or delirium (8%)
• Extrapyramidal Signs (7%)

Most helpful Signs in making the diagnosis:

• Abnormal ocular movements, which include, blinking, twitching of the eyelids, pupillary dilatation, gaze deviation or nystagmus have a greater than 80% specificity of NCSE.
• Automatisms and motor twitches of the face or extremities have a low specificity of 44%.

Mimics of NCSE

Given the low specificity of signs and symptoms we need to beware of potential mimics.

1. Postictal State: This is the most common and occurs consciousness is impaired following a seizure. It may persist for hours. In these patients benzodiazepines will not improve mental status.
2. Encephalopathy: This is the second most common and can be due to toxic ingestion, infection, sepsis or shock. Motor movements are multifocal and do not tend to include the perioral region or eyelids. Automatisms do not tend to occur
3. Catatonia: Unresponsiveness and inability to move in an awake patient. It is associated with schizophrenia, bipolar disease and PTSD.
4. Encephalitis: Presents with viral-like prodrome, followed by psychiatric signs and symptoms, change in mental status, dyskinesia and movement disorders. There is inflammation of cerebral tissue.
5. Anticholinergic Activity: Due to anticholinergic toxicity and presents with nonreactive mydriasis, delirium, hallucinations, urinary retention, anhidrosis  and tachycardia.
6. Serotonin Syndrome: Due to serotonergic medication. Presentation is with altered mental status, autonomic instability, hyperthermia, labile blood pressures, clonus, rigidity, tremors and hyperreflexia.
7. Neuroleptic Malignant Syndrome: Due to Neuroleptic Agents. Develops over several days with altered mental status, muscle rigidity, hyperthermia and autonomic instability.
8. Stroke: Ischaemic or haemorrhagic

References

1. Long B, Koyfman A. Nonconvulsive Status Epilepticus: A Review for Emergency Clinicians. The Journal of Emerg Med. Vol. 65, No. 4, pp. e259–e271, 2023.