Syncope: an epileptiform EEG made seizures more likely.

Clinical bottom line (level 4)

  1. A third of patients referred to neurology clinic with transient loss of consciousness had experienced a seizure.
  2. Epileptiform activity on EEG made a seizure more likely (LR+7.4) , but a normal EEG could not safely rule it out.
  3. An abnormal hyperventilation test made a seizure less likely (LR-0.29) , but could not safely rule it out.
Hoefnagels et al: Journal of Neurology, Neurosurgery, and Psychiatry 1991; 54: 953-956
Expires December 2004

The study

Setting: neurology outpatients clinic, university hospital, the Netherlands

119 patients (aged ?, 53% male) with on or more episodes of transient loss of consciousness (lasting < 1 hour with an inability to maintain posture or recall events during episode)

Excluded if
  • aged < 15
  • loss of consciousness due to trauma or subarachnoid haemorrhage
  • epilepsy



    • ?independent blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
    Reference standard:
    • Any of
      • eyewitness observed more than a few movements during loss of consciousness and identified clonic movements when imitated by the interviewer
      • eyewitness observed automatisms (chewing, lip-smacking) during loss of consciousness
      • patient reported an unequivocal aura (e.g. strange smell) preceding event
      • patient felt confused immediately after the event (inability to recognise familiar persons or environment)
      • tongue-biting
    Diagnostic test:
    • 21-channel EEG
    • hyperventilation test (if aged < 65) - breathing at 40 breaths/minute for at least 3 minutes - positive if <90% baseline end-tidal carbon dioxide after 3 minutes, and at least 2 symptoms provoked
    • 12-lead ECG

    The evidence

    pre-test probability of seizure: 38%, (95% CI: 29% to 47%)

    diagnostic test seizure syncope LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    EEG 18 4 7.4
    (2.7 to 21)     		82% 0.63
    (0.50 to 0.81)     		28%
    total 45 74


    diagnostic test seizure syncope LR
    (95% CI)    		 post-test probability
    negative hyperventilation test 18 12 1.9
    (1.1 to 3.4)     		60%
    dubious hyperventilation test 13 8 2.0
    (0.94 to 4.4)     		62%
    positive hyperventilation test 6 26 0.29
    (0.13 to 0.62)     		19%
    total 37 46

    Comments

    1. 18 ECGs were abnormal, but only 3 were diagnostic.
    2. Laboratory tests were not helpful at diagnosing seizure or syncope.

    Citation

    1. Hoefnagels WA, Padberg GW, Overweg J, et al: syncope or seizure? The diagnostic value of the EEG and hyperventilation test in transient loss of consciousness. Journal of Neurology, Neurosurgery, and Psychiatry 1991; 54: 953-956
    Search Terms: syncop* and seizure in PubMed clinical searches ('diagnosis' and 'specificity')
    Contributor: Chris Ball and Clare Wotton, December 1999
    Reviewer:

    Clinical Question.
    Patient transient loss of consciousness
    Intervention or Exposure EEG, hyperventilation test
    Outcome seizure