Differential Diagnosis

As previously noted, clinical examination is often normal in syncope, so differentiation from other causes of collapse is usually based on the history.

Epileptic seizure

May be preceded by aura. Post ictal state common. Unlikely if recovery is rapid.

Cardiac arrythmia

Abrupt onset of LOC, usually with no warning, rapid recovery. CV risk factors common. Unlikely in younger patients in the absence of cardiac history. Exercise induced syncope always warrants further investigation.

Cardiac outflow obstruction

Symptoms on exercise; rapid recovery usual. Absence of murmur at rest does not exclude cardiac outflow obstruction. Unlikely in the absence of mechanical valves, exertional murmur, or evidence of ventricular hypertrophy.


Usually gradual onset with prodromal symptoms. Unless given glucose recovery may be slow and incomplete.

Pulmonary embolus

Abrupt loss of consciousness. Tachypnoea usual after recovery. Unlikely in low risk patients.

Basilar artery migraine

Although a rare diagnosis, it is more common in young women, who may be aware of specific triggers.

Vertebrobasilar insufficiency

Vertigo, nausea, dysphagia and dysarthria common. Transient loss of consciousness is rarely the sole presenting symptom.

This list of differential diagnoses is not exhaustive, and a clinician must be open-minded when considering any possible diagnosis.