Differential Diagnosis for Unconsciousness

Immediate Life-Threatening Causes

Any unconscious patient with absent or abnormal breathing should be assumed to be in cardiac arrest until proven otherwise, according to the American Heart Association 1, 2
Healthcare providers should check for a pulse for no more than 10 seconds; if no definite pulse is felt, assume cardiac arrest and begin CPR immediately, as recommended by the American Heart Association 1
Agonal breathing is present in 40-60% of cardiac arrest victims and is commonly misinterpreted by rescuers as adequate breathing, leading to delayed resuscitation, warns the American Heart Association 1
Agonal breathing appears as slow, irregular gasping respirations that are ineffective for ventilation and may be described as abnormal breathing, snoring, or gasping, according to the American Heart Association 1

Reflex syncope is the most common cause of transient loss of consciousness, affecting one in four people at least once in their lifetime, reports the European Society of Cardiology 3
Typical triggers for reflex syncope include pain, emotion, seeing blood, blood draws, and prolonged standing, notes the European Society of Cardiology 3
Prodromal symptoms for reflex syncope include nausea, sweating, and pallor before the attack, according to the European Society of Cardiology 3
Unconsciousness from reflex syncope typically lasts less than one minute with rapid return to full consciousness, though post-event fatigue is common, states the European Society of Cardiology 3
Brief myoclonic movements and incontinence can occur in reflex syncope but do not indicate epilepsy, clarifies the European Society of Cardiology 4
Orthostatic hypotension results from inadequate blood pressure compensation upon standing, distinguishes the European Society of Cardiology 3
Orthostatic hypotension is distinguished from reflex syncope by the absence of specific triggers and the direct relationship to postural change, explains the European Society of Cardiology 5

Key distinguishing features of epileptic seizures from syncope include tonic-clonic movements, tonic posture, and post-ictal confusion or sleepiness, highlights the European Society of Cardiology 4
Tonic-clonic movements are massive, synchronous jerks of arms/legs, whereas brief myoclonic jerks are common in syncope, notes the European Society of Cardiology 4
Tonic posture involves forceful extension of extremities, according to the European Society of Cardiology 5
Movements can occur before the fall in epilepsy, versus after falling in syncope, states the European Society of Cardiology 3
Post-ictal confusion or sleepiness lasting more than a few minutes strongly suggests epilepsy, warns the European Society of Cardiology 4
Tongue biting and muscle pains lasting hours to days indicate seizure, reports the European Society of Cardiology 4
Urinary incontinence is not useful for distinction between syncope and seizure, clarifies the European Society of Cardiology 4
Absence epilepsy and partial complex epilepsy cause altered, not lost, consciousness and do not typically cause falls, notes the European Society of Cardiology 4
Transient ischemic attacks are extremely unlikely to cause true loss of consciousness, states the European Society of Cardiology 4
Only vertebrobasilar TIAs may theoretically cause unconsciousness, but other neurological signs predominate, explains the European Society of Cardiology 4

Psychogenic pseudosyncope exhibits signs of unconsciousness when somatic brain function is normal, reports the European Society of Cardiology 5
No cerebral hypoperfusion occurs during psychogenic pseudosyncope episodes, notes the European Society of Cardiology 5
Psychogenic pseudosyncope is distinguished by normal vital signs and lack of physiological changes during apparent unconsciousness, states the European Society of Cardiology 5
Cataplexy is a partial or complete loss of muscular control triggered by emotions, usually laughter, and the patient maintains full recollection of events, explains the European Society of Cardiology 4
Cataplexy most often occurs as part of narcolepsy syndrome, notes the European Society of Cardiology 4

Early recognition of cardiac arrest and immediate CPR improves survival by 2- to 3-fold, according to the American Heart Association 1
The risk of injury from CPR in patients who are unconscious but not in cardiac arrest is low and does not outweigh the benefit of early intervention, states the American Heart Association 1
Accurate diagnosis between syncope and epilepsy has profound implications for long-term management, driving restrictions, and quality of life, highlights the European Society of Cardiology 4

The European Society of Cardiology recommends that classical vasovagal syncope is diagnosed when precipitating events are associated with typical prodromal symptoms 6
The European Society of Cardiology suggests that orthostatic hypotension is diagnosed when syncope occurs with documented blood pressure drop ≥20 mmHg systolic after standing for 3 minutes 6
The European Society of Cardiology states that cardiac arrhythmia is diagnosed by ECG showing specific patterns, including sinus bradycardia <40 bpm with pauses >3 seconds, and that red flags include syncope during exertion or while supine 6

The European Heart Journal notes that tongue biting and muscle pains lasting hours to days indicate seizure, and that complete flaccidity during unconsciousness argues against epilepsy 7
The European Heart Journal states that absence epilepsy and partial complex epilepsy cause altered consciousness, and that patients remain upright during attacks 7
The European Heart Journal suggests that vertebrobasilar TIAs may theoretically cause unconsciousness, but focal neurological signs always predominate, and that carotid artery TIA does not cause loss of consciousness 7

The European Heart Journal recommends psychiatric evaluation when psychogenic pseudosyncope is suspected, and that tilt testing with concurrent EEG and video monitoring may be considered 7
The European Heart Journal notes that cataplexy is a partial or complete loss of muscular control triggered by emotions, with full recollection of events, and that the patient maintains consciousness 7