16B. Differential diagnosis of short-term loss of consciousness

Page created on June 3, 2021. Last updated on May 31, 2022 at 08:32

It’s important to be able to distinguish syncope from epileptic seizure, as both cause short-lasting loss of consciousness, but the management for each is different. In the differential diagnosis, obtaining both patient and eyewithness history is important.



Syncope refers to transient loss of consciousness due to cerebral hypoperfusion. The majority of short-lasting losses of consciousness are syncope.

Convulsive syncope is a form of syncope which is accompanied by myoclonic jerks and tonic stretching. Its clinical importance lies in that convulsive syncope may be mistaken as epileptic seizure by laymen. However, those who are familiar with the appearance of epileptic seizures can usually differentiate them visually.


  • Cardiac syncope
    • Arrhythmia
    • Valvular disease
    • Hypertrophic cardiomyopathy
    • Pulmonary embolism
  • Reflex syncope
    • Vasovagal syncope – emotional stress, prolonged standing, pain
    • Situational syncope – urination, coughing, defecation
    • Carotid sinus syndrome – pressure on carotid sinus
  • Orthostatic hypotension
    • Autonomic dysfunction
    • Postural tachycardia syndrome
    • Antihypertensive drugs
    • Dehydration

Clinical features

Unlike epileptic seizures, convulsive syncope has the following clinical features:

  • Presence of prodromal symptoms
    • Blurry vision, sight goes dark
    • Sweating
  • Usually brief (< 20 seconds)
  • Patient slowly collapsed on the floor
  • Tongue bite absent or on the apex of the tongue (not on the lateral side as in epileptic)
  • Always starts with atonic phase, never tonic phase. But may have some tonic stretching
  • Doesn’t have true clonus, rather myoclonic jerks
  • Eyes remain open
  • No post-convulsive confusion, the patient recovers immediately

Enuresis is more common in epileptic seizures but may also occur in convulsive syncope.


The clinical features which suggest epileptic seizures rather than syncope are:

  • Absence of prodromal symptoms (often sudden blackout)
  • Lasts minutes
  • Enuresis
  • Patient fell immediately
  • Bitten tongue on lateral part
  • Patient has postictal period of confusion, stupor, muscle pain, manesia, aphasia, or Todd paresis

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