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Presyncope / Syncope



Presyncope is a feeling of lightheadedness or of being about to 'faint'. Syncope is the transient loss of consciousness, or the act of 'fainting'.
Often patients present with 'dizziness', which may refer to lightheadedness, vertigo, motor instability or anxiety. It is important to gain further history and differentiate between these symptoms.


  • Causes of Presyncope / Syncope

  • Neurally Mediated

  • Vasovagal syncope
  • Situational - coughing, micturition, defaecation, playing brass instruments, valsalva
  • Carotid sinus syndrome - hypersensitivity of the carotid sinus
  • Cardiac

  • Arrhythmia - sick sinus, AV block, SVT, AF, VT
  • Structural - aortic stenosis, acute coronary syndrome, obstructive cardiomyopathy
  • Orthostatic

  • Volume loss - dehydration, haemorrhage
  • Primary autonomic failure - Parkinson's, multisystem atrophy, MS
  • Secondary autonomic failure - diabetic neuropathy, amyloidosis, HIV neuropathy, CIPD
  • Drugs - antihypertensives, vasodilators, diuretics, antidepressants
  • Cerebrovascular

  • Stroke / TIA
  • Vascular steal syndrome
  • Other

  • Pulmonary embolism

Differential Diagnosis

  • Differential Diagnosis for Dizziness

  • Spinning Sensation - that the patient or the room is spinningVertigo, i.e. vestibular pathology
  • Lightheadedness - a feeling of nearly faintingPresyncope
  • Dysequilibrium - a feeling of poor balanceGait disorder
  • Overwhelmed sensation - a disconnection from the worldAnxiety
  • Differential Diagnosis for Loss of Consciousness

  • Intracranial

  • Haemorrhage - intracerebral, subarachnoid, subdural, extradural
  • Infarction
  • Infection - meningitis, encephalitis, abscess
  • Tumour - mass effect, cerebral oedema
  • Post ictal state
  • Head trauma - vascular, hypoxia, cerebral oedema, parenchymal injury
  • Psychiatric - conversion, depression, catatonia
  • Extracranial

  • Cardiovascular - shock, hypertension
  • Infection - septicaemia
  • Metabolic - hypo/hyperosmolar states, hypo/hyperglycaemia, hypothyroidism, hypopituitarism, electrolyte abnormality, hypoxia, hepatic failure, renal failure
  • Endocrine - adrenal crisis, myxoedema coma
  • Drugs / toxins - sedatives, analgesics, alcohol
  • Physical injury - hyper / hypothermia, electrocution

History of Presenting Complaint

  • Trigger

    Whether there was anything that may have precipitated the presyncope or syncope.
  • Standing after lying / sittingSuggestive of vasovagal syncope or orthostatic hypotension
  • NOT triggered by postural changeSuggestive of arrhythmia
  • Pain or emotional stressVasovagal syncope
  • Venesection or seeing bloodVasovagal syncope
  • EatingSituational (postprandial) syncope
  • Micturition or defaecationSituational (micturition / defaecation) syncope
  • Paroxysm of coughSituational syncope
  • Weightlifting or playing a brass instrumentSituational (weightlifter's / trumpet player's) syncope
  • Head rotation or wearing a tight collarSuggestive of carotid sinus syndrome
  • ShavingSuggestive of carotid sinus syndrome
  • ExerciseSuggestive of arrhythmia or cardiac structural disease
  • Arm exercisesSuggestive of vascular steal syndrome
  • Before the Episode

    Whether the patient had any symptoms just prior to the episode of syncope.
  • LightheadednessSuggestive of syncope, rather than seizure
  • Nausea, flushing and diaphoresisSuggestive of vasovagal syncope
  • Chest pain +/- diaphoresisSuggestive of acute coronary syndrome or pulmonary embolism
  • Arm / leg weakness or facial droopSuggestive of stroke / TIA
  • Shortness of breathMay represent heart failure in the setting of aortic stenosis
  • PalpitationsSuggestive of arrhythmia
  • Visual changes or altered sense of smellSuggestive of preictal state
  • During the Episode

  • Loss of consciousness for a few secondsMore suggestive of syncope than seizure
  • Short episode of myoclonic movementMore suggestive of vasovagal than seizure
  • Tonic-clonic movementsSuggestive of seizure rather than syncope
  • Tongue biting or urinary incontinenceSuggestive of seizure rather than syncope
  • After the Episode

  • Nausea and vomitingSuggestive of vasovagal syncope
  • Short period of disorientationMay occur post vasovagal
  • ConfusionSuggestive of post-ictal period
  • Arm / leg weakness or facial droopSuggestive of stroke / TIA
  • Timing

  • The frequency and duration of these episodes.
  • Associated Symptoms

    Whether the patient has been unwell recently.
  • Vomiting or diarrhoeaSuggestive of orthostatic hypotension due to volume loss
  • PR bleeding, malaena or haematemesisSuggestive of orthostatic hypotension due to volume loss
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