Episodic Loss of Consciousness

Differential Diagnosis

Common Diagnoses

Occasional Diagnoses

  • Cardiac Structural Lesion (e.g. Aortic Stenosis, Hypertrophic Obstructive Cardiomyopathy, Pulmonary Stenosis)
  • Micturition and Cough Syncope
  • Sleep Apnoea
  • Valsalva-Induced Syncope (e.g. Weightlifting)
  • Pseudoseizures

Rare Diagnoses

Ready Reckoner

Key distinguishing features of the most common diagnoses

Vasovagal AttackArrhythmia EpilepsyHypoglycaemiaOrthostatic Hypotension
Prodromal SymptomsYesNoPossiblePossiblePossible
Trigger FactorsYesNoPossibleYesYes
Slow RecoveryNoNoYesYesNo
Abnormal Resting ECGNoPossibleNoNoNo

Possible Investigations

Likely:FBC; ECG (especially in elderly); if probable epilepsy, also EEG and CT scan.

Possible:Glucometer, 24 h ECG/event monitor.

Small Print:Echocardiography, tilt-table testing.

  • Glucometer ‘on the scene’ gives diagnosis of hypoglycaemia.
  • FBC: Anaemia will exacerbate any form of syncope and TIAs.
  • Standard ECG may reveal signs of ischaemia and heart block; 24 h ECG/event monitor more useful for definitive diagnosis of arrhythmia.
  • CT scan and EEG essential if previously undiagnosed epilepsy suspected.
  • Echocardiography: If structural cardiac problem suspected.
  • Tilt-table testing: For unexplained syncope to assess susceptibility to vasovagal episodes.

Top Tips

  • The key to diagnosis is an accurate history. This may not be available from the patient, so make a real effort to obtain an eyewitness account.
  • In younger patients, the diagnosis is likely to lie between a vasovagal attack and a fit; in the middle-aged and elderly, the differential is much wider and will include, for example, arrhythmias and orthostatic hypotension.
  • Episodic loss of consciousness is a symptom which merits diligent assessment. An accurate diagnosis has implications not only for the individual’s health, but also for employment and driving.
  • Remember that, with a vasovagal episode, patients remaining upright (e.g. sitting or in a crowd) may develop tonic–clonic movements which mimic a fit.
  • Unlike in syncope or seizures, the eyes are usually closed in pseudoseizures.

Red Flags

  • An eyewitness account that the patient looked as though he or she had died, together with marked facial flushing on recovery, is characteristic of Stokes–Adams attacks. These can be fatal, so early diagnosis is important.
  • Discovery of an aortic stenotic murmur should prompt urgent referral. Severe aortic stenosis can cause sudden cardiac death.
  • Red flags suggesting a possible cardiac cause include a family history of sudden cardiac death, syncope during exercise and an abnormal ECG.
  • Syncope caused by neck pressure or head movement could be carotid sinus syncope – if recurrent, this will require a pacemaker.
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