Non-convulsive Status Epilepticus

Created on Tue, 06/30/2015 - 23:45
Last updated on Thu, 09/24/2015 - 04:20

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:

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

Non-convulsive status epilepticus is defined as seizure activity seen on EEG without the clinical findings associated with convulsive status epilepticus.

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:

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
Outcome Statistics for Non-Convulsive Status Epilepticus

 

 

References

Oh's Intensive Care manual:

Chapter 49   (pp. 549) Disorders  of  consciousness  by Balasubramanian  Venkatesh

Chapter   50   (pp. 560) Status  epilepticus  by Helen  I  Opdam

Fountain, Nathan B. "Status epilepticus: risk factors and complications."Epilepsia 41.s2 (2000): S23-S30.

Meierkord, Hartmut, and Martin Holtkamp. "Non-convulsive status epilepticus in adults: clinical forms and treatment." The Lancet Neurology 6.4 (2007): 329-339.

Scholtes, Frans B., Willy O. Renier, and Harry Meinardi. "Non-convulsive status epilepticus: causes, treatment, and outcome in 65 patients." Journal of Neurology, Neurosurgery & Psychiatry 61.1 (1996): 93-95.

Husain, A. M., G. J. Horn, and M. P. Jacobson. "Non-convulsive status epilepticus: usefulness of clinical features in selecting patients for urgent EEG."Journal of Neurology, Neurosurgery & Psychiatry 74.2 (2003): 189-191.

Haffey, S., A. McKernan, and K. Pang. "Non-convulsive status epilepticus: a profile of patients diagnosed within a tertiary referral centre." Journal of Neurology, Neurosurgery & Psychiatry 75.7 (2004): 1043-1044.

Jirsch, J., and L. J. Hirsch. "Nonconvulsive seizures: developing a rational approach to the diagnosis and management in the critically ill population."Clinical neurophysiology 118.8 (2007): 1660-1670.

Rupprecht, Sven, et al. "Levetiracetam as a treatment option in non-convulsive status epilepticus." Epilepsy research 73.3 (2007): 238-244.