What is the differential diagnosis and initial management of unconsciousness?

Differential Diagnosis of Unconsciousness

Immediate Life-Threatening Assessment

Any unconscious patient with absent or abnormal breathing must be assumed to be in cardiac arrest until proven otherwise, and CPR should be initiated immediately if no definite pulse is felt within 10 seconds. 1

• Agonal breathing (slow, irregular gasping) occurs in 40-60% of cardiac arrest victims and is commonly misinterpreted as adequate breathing, leading to fatal delays in resuscitation 1
• Early recognition and immediate CPR improves survival by 2- to 3-fold, and the risk of injury from CPR in non-arrest patients is negligible compared to the benefit of early intervention 1

Major Diagnostic Categories

1. Cardiovascular Causes (Most Common)

Reflex (Neurally-Mediated) Syncope:

• Affects one in four people at least once in their lifetime, making it the most common cause of transient loss of consciousness 1
• Key diagnostic features: Triggered by pain, emotion, seeing blood, blood draws, or prolonged standing; preceded by nausea, sweating, and pallor; unconsciousness lasts <1 minute with rapid recovery (though post-event fatigue is common) 1
• Brief myoclonic jerks and incontinence can occur but do not indicate epilepsy 1
• Classical vasovagal syncope is diagnosed when precipitating events (fear, severe pain, emotional distress, instrumentation, prolonged standing) are associated with typical prodromal symptoms 2

Orthostatic Hypotension:

• Distinguished by direct relationship to postural change without specific triggers 1
• Diagnosed when syncope occurs with documented blood pressure drop ≥20 mmHg systolic (or systolic BP <90 mmHg) after standing for 3 minutes 2
• Measure blood pressure after 5 minutes supine, then each minute after standing 2

Cardiac Arrhythmia:

• Diagnosed by ECG showing: sinus bradycardia <40 bpm with pauses >3 seconds, Mobitz II or 3rd degree AV block, alternating bundle branch block, rapid paroxysmal SVT/VT, or pacemaker malfunction 2
• Red flags: Syncope during exertion or while supine, preceded by palpitations or chest pain, family history of sudden death, presence of severe structural heart disease 2

2. Neurological Causes

Epileptic Seizures:

• Distinguishing features from syncope: Tonic-clonic movements (massive, synchronous jerks) versus brief myoclonic jerks in syncope; tonic posture (forceful extension of extremities); movements occur before the fall (versus after falling in syncope) 1
• Post-ictal confusion or sleepiness lasting >few minutes strongly suggests epilepsy 1
• Tongue biting (lateral tongue, not tip) and muscle pains lasting hours to days indicate seizure 1, 2
• Complete flaccidity during unconsciousness argues against epilepsy (except rare atonic seizures in children with pre-existing neurological problems) 2
• Urinary incontinence is not useful for distinguishing syncope from seizure 1
• Important: Absence epilepsy and partial complex epilepsy cause altered (not lost) consciousness and patients remain upright during attacks 2

Stroke/TIA:

• Transient ischemic attacks are extremely unlikely to cause true loss of consciousness 1
• Only vertebrobasilar TIAs may theoretically cause unconsciousness, but focal neurological signs (limb weakness, ataxia, oculomotor palsies, oropharyngeal dysfunction) always predominate 2, 1
• Carotid artery TIA does not cause loss of consciousness 2

Structural Brain Lesions:

• Unconsciousness results from disturbance of either the reticular activating system or both cerebral hemispheres 3
• CT scan of the head is the basic neurological examination, adequately revealing common intracranial causes 3

3. Metabolic/Toxic Causes

• The cause of unconsciousness is usually metabolic or toxic, with structural/intracranial causes comprising the remainder 3
• Common causes include: Stroke, diabetic complications and emergencies, metastatic neoplasm, HIV/AIDS-related disease, and hypertensive emergency 4
• Consider benzodiazepine overdose, which can be reversed with flumazenil (initial dose 0.2 mg IV over 30 seconds, titrated up to cumulative 3-5 mg) 5

4. Conditions Mimicking Unconsciousness

Psychogenic Pseudosyncope:

• Signs of unconsciousness when somatic brain function is normal, with no cerebral hypoperfusion 1
• Distinguished by normal vital signs and lack of physiological changes during apparent unconsciousness 1
• Psychiatric evaluation is indicated when suspected; tilt testing with concurrent EEG and video monitoring may be considered 2

Cataplexy:

• Partial or complete loss of muscular control triggered by emotions (usually laughter), with full recollection of events 1
• Patient maintains consciousness, so there is no amnesia 2
• Most often occurs as part of narcolepsy syndrome 1

Initial Management Priorities

Immediate Actions:

1. Confirm vital functions and assume cardiac arrest if breathing is absent/abnormal until pulse confirmed 1, 3
2. Ensure clear airway (unconscious patients have obstructed airways because the tongue slides back) by lifting the jaw, possibly with oropharyngeal airway 6
3. Place in semi-prone position if not actively managing airway 6
4. Check for head/neck injuries, meningism, pupillary inequality, and papillary stasis 3

Assessment Tools:

• Use Glasgow Coma Scale (GCS) for initial evaluation; GCS ≤13 indicates significant impairment 7
• For severely affected, intubated, or suspected brainstem-injured patients, prioritize the FOUR score over GCS 8, 7
• For prolonged disorders of consciousness, the Coma Recovery Scale-Revised (CRS-R) is the reference tool for distinguishing vegetative state/unresponsive wakefulness syndrome from minimally conscious state 8

Diagnostic Workup:

• Both radiological (CT head) and laboratory investigations are usually required 3
• Consider instrumental techniques (PET-FDG, fMRI, high-density EEG, TMS-EEG) as part of multimodal evaluation in non-responsive patients to detect consciousness when behavioral assessment is inconclusive 8

Critical Pitfalls to Avoid

• Do not delay CPR based on uncertainty about cardiac arrest status; agonal breathing is commonly misinterpreted 1
• Do not assume absence of consciousness based solely on lack of behavioral response; instrumental techniques may reveal preserved consciousness 8
• Do not diagnose epilepsy based on brief myoclonic movements or incontinence alone during syncope 1
• Do not attribute unconsciousness to TIA without prominent focal neurological signs 2, 1
• Sedation, analgesics, and neuromuscular blockade affect assessment scores, particularly respiratory components in ventilated patients 8
• Hypoxia from obstructed airways causes cerebral ischemia and cardiac arrest within 5-6 minutes 6