Non-convulsive status epilepticus

For whatever reason, the College loves non-convulsive status epilepticus. It has come up many times as one of the differentials. Notable occurences where it was the cheif topic of an SAQ include Question 20 from the second paper of 2012.

Oh's Manual explores this this issue in Chapter 49 (pp. 549, "Disorders  of  consciousness")  by Balasubramanian  Venkatesh, and Chapter 50 (pp. 560, " Status  epilepticus"  by Helen  I  Opdam.

Additional (free to read) resources could be scraped up from the internet:

• A good review from the Lancet (2007)
• An older BMJ observational study (1996)

Features unique to non-convulsive status epilepticus

Briefly, in order to qualify for this label, one must become "altered" in one's level of consciousness, and to sustain this alteration for over 30 minutes. An EEG with epileptiform discharges is required to confirm the diagnosis. Another helpful hint is the paradoxical restoration of normal alertness following the administration of an IV benzodiazepine.

One should think carefully about non-convulsive status epilepticus in any patient in whom the decreased level of consciousness has not been explained by higher-yield investigations. Statistically speaking, one study has dicovered that among patients with undiagnosed coma, roughly 8% have the characteristic epileptiform discharges on their EEG.

Definition

Clinical features of non-convulsive status epilepticus

Negative symptoms: anorexia, aphasia/ mutism amnesia catatonia confusion, coma lethargy fixed-gaze staring.

Positive symptoms: agitation/aggression automatisms uncontrollable blinking delirium, delusions, psychosis echolalia facial twitching (particularly, small periorbital muscles) nystagmus/eye deviation

• In one study of clinical features of NCSE, "none of the clinical features evaluated had a high sensitivity and specificity individually. However, the combined sensitivity for “remote risk factors for seizures” and “eye movement abnormalities” was 100%." Remote risk factors in this situation included previous stroke, neurosurgical intervention, brain tumour, history of meningitis, and so on.

Oh's Manual also suggests some duration criteria, suggesting that one must become "altered" in one's level of consciousness for over 30 minutes in order for this sort of epileptic activity to be called a "status" of any sort.

An EEG with epileptiform discharges is required to confirm the diagnosis. Another helpful hint is the paradoxical restoration of normal alertness following the administration of an IV benzodiazepine.

One should think carefully about non-convulsive status epilepticus in any patient in whom the decreased level of consciousness has not been explained by higher-yield investigations. Statistically speaking, one study has dicovered that among patients with undiagnosed coma, roughly 8% have the characteristic epileptiform discharges on their EEG.

Difficulties in diagnosis of non-convulsive status

Why is this diagnosis difficult to make, and so frequently missed?

• Non-specific clinical features.
• No agreement on the diagnostic criteria by which to identify this condition.
• The most frequently agreed upon criteria are non-clinical (i.e. they rely on EEG to identify epileptiform activity)
• Even when EEG is available, EEG findings are frequently non-specific which should also be interpreted as features of encephalopathy (The most recent (2012) Guidelines suggest that even vaguely rhythmic suspicious-looking EEG findings should be treated as NCSE).

Risk factors for non-convulsive status epilepticus

A study from Belfast reported on some risk factors identified among a series of patients with NCSE.

It should be added that even though the college lists these risk factors in Question 20, in fact this is from a well-established association. From over 1800 inpatient EEGs, there were 50 episodes of NCSE identified, and from this substrate the following risk factor profile was produced

• Known epileptic with an acute infection
• Recent convulsive seizures
• Remote risk factors for seizures:
  • previous stroke
  • tumour
  • neurosurgery
  • dementia
  • multiple sclerosis
  • encephalitis or meningitis

Management of non-convulsive status epilepticus

The 2012 Guidelines for Management, referred to extensively in the summary of convulsive status epilepticus, do not offer anything specific for this condition. A different article from Clinical Neurophysiology (2007) also canot add anything specific. Oh's Manual recommends valproate and levitiracetam; of these the latter seems to be gaining popularity, given its relative safety.

Outcomes

The 2012 Guidelines for Management etc etc contain within them a huge table (Table 4) on Page 7, which patiently lists the mortality statistics for all sorts of status epilepticus. From this table, one can isolate some NCSE-specific information:

Outcome Statistics for Non-Convulsive Status Epilepticus

Mortality: At hospital discharge: 18-52% At 30 days: 65% Time-critical diagnosis: Diagnosis within 30 min of seizure onset: mortality 36 % Diagnosed 24 hr after seizure onset: mortality 75 %

Features associated with poor outcome: Severe mental status impairment Longer seizure duration Less than 10hrs: 10% mortality More than 20hrs: 85% mortality Unknown cause