Loss of Consciousness (LOC) – 1

What to do for the patient with the chief complaint of, sometime recently, having “passed out.”  Today they look perfectly well, alert & oriented.  You’ll wind up performing a cardiac & neurologic exam, which are invariably normal.  Diagnosis will be made entirely by history.

The differential diagnosis for Altered Mental Status, Seizure, or Coma, right here and now, is a lot more complicated.  It includes a wide range of possibilities including brain masses, hyponatremia, sepsis, etc. etc.  I learned the mnemonic “Vowel TIPS.”

But for the person who had a “spell” or “episode” that’s over & done with, and now feels fine, it’s more limited.  This is our current topic.  Remember, even though you may wind up ordering various tests, you’ll have to distinguish among the following entities by history alone.

History of Loss of Consciousness  —  Differential Diagnosis

Fell to Floor

Amnesia (without Fall)


Witnesses are obviously especially helpful.  If they didn’t accompany the patient to your office, call them.  If the patient doesn’t know how to reach them, have them try to find out & let you know tomorrow.  Query witnesses systematically to rule-out or rule-in the above conditions.

Patient Fell to the Ground

Syncope  —  A simple faint
  • Duration of LOC <30 secs.
  • Regains consciousness immediately; may feel sleepy or fatigued for several minutes, but is alert
  • Often a trigger (e.g. sight of blood) — see below
  • May include very brief tonic-clonic movements
  • Head trauma caused by faint might rarely confuse the picture
Seizure  —  Generalized tonic-clonic (a.k.a. “Grand Mal”)
  • Duration 20-90 seconds (maybe longer)
  • Tonic-clonic movements
  • Maybe Cyanosis
  • Maybe foaming at mouth, abnormal eye movements
  • Maybe tongue biting, incontinence
  • Gradual recovery to alertness, headache common (post-ictal phase)
Head Trauma  —  Witnesses describe LOC occurs immediately post-trauma
  • As opposed to fainting occurring first, patient then hitting head upon fall
Transient Ischemic Attack (TIA)  —  Basilar artery
  • May recall severe Vertigo
  • Prior episodes of posterior circulation symptoms: vertigo, diplopia, dysarthria, dysphagia, ataxia, visual field loss, contralateral facial/body numbness
  • Stroke risk factors (but these are also risks for cardiac syncope)
Hyperventilation  —  due to acute Anxiety
  • Witnesses note the rapid breathing
  • Patient recalls feeling dizzy, with paresthesias of lips & fingers
  • Duration of LOC is brief (unless conversion reaction follows)
  • Auscultate lungs rapidly & extensively: if patient reports same dizziness & paresthesias as with event, diagnosis made
Conversion Reaction  —  Psychiatric “escape” from intolerable situation
  • Duration: anything (often prolonged)
  • Any “jerking” movements are random, not stereotypic
  • Forced eye closure or crying [never occurs with seizures]
  • Biting on tip of tongue or lip (seizures bite on side of tongue)
  • Maybe fluctuating level of consciousness
  • Patient had awareness of environment (can describe what witnesses did)

Key Clarification:  In a generalized seizure, there is complete loss of awareness until recovery occurs after the post-ictal phase.  As such, there’s amnesia for the entire event.  For complete LOC to alternate with lucidity is not compatible with organic illness [think conversion Reaction].  Of course, a person can seize, begin to recover, then seize again.  This qualifies as Status Epilepticus, but is life-threatening, pretty rare, & highly unlikely to have resolved on its own.

Faint versus Seizure: one expert commented, “Ask what the witnesses did.”  If they ran toward the patient, it was a faint; if they ran away, think seizure. [joke]

Patient Did Not Fall

Seizure  —  Complex-Partial (without generalization)
  • Onset: Staring; Lip-smacking / grimacing
  • May include a variety of behaviors / utterances
  • Loss of awareness of environment (total amnesia for event)
  • Duration:  Seizure <4 min.  Post-ictal maybe 1-2 hrs.
Dissociative State  —  Usually occurs without witnesses present
  • Loss of awareness for environment
  • Period of amnesia may last hours
  • If witnesses present, may describe mood-related behaviors (e.g. outbursts)
Transient Global Amnesia  —  Acute onset inability to form new memories
  • Age >50, usually older
  • Duration 1-10 hours
  • Confusion; patient asks repeated questions
  • Not disoriented to person (knows own name)
  • Maybe some amnesia for past events (retrograde)
  • No loss of awareness of environment
  • Able to perform complex tasks (e.g. drive, cook, play piano, etc)

Some explanations:

A Complex-Partial Seizure is a true neurologic event with EEG abnormalities.  Synonyms include “Psychomotor” and “Temporal Lobe” seizures / epilepsy.  There’s only a fall with tonic-clonic movements if it generalizes.  It involves “automatisms” such as facial movements, word repetitions, even walking or undressing.  Duration is a matter of minutes, followed by post-ictal confusion, with complete amnesia for the event.  The post-ictal phase can be brief, or last up to 2 hours.

I had a blind AIDS patient with complex-partial seizures, described as episodes of complete amnesia.  At one visit, he commented he’d just had one, en route to the clinic with his health worker.  So I asked the health worker, “What happened?  What did you talk about?”  He replied, “Nothing.  He [patient] was in his own mood, just mumbled, didn’t feel like talking.”   The health worker had actually accompanied a patient in the midst of a seizure, & didn’t realize it!

A Dissociative State is when a person loses awareness due to psychiatric mechanisms that preoccupy them with inescapable thoughts, invariably trauma-related (PTSD).  They “trance-out,” become unresponsive, and have amnesia for the episode.  It usually occurs when the person is alone, thus not distracted.  See the movie Primal Fear with Richard Gere and Edward Norton, [entertaining though not first-rate; R-rated, may offend some devoutly religious].

Transient Global Amnesia (TGA)  —  A newly-recognized (1956) syndrome in which a usually-older person suddenly becomes unable to form new memories, & to recall some old ones.  They know who they are, but are profoundly disoriented as to what is occurring to them.  It lasts less than a day, usually doesn’t recur, & has defied definition as a neurologic, vascular, or psychogenic phenomenon.  TGA is usually so blatant and concerning to anyone in contact with the person, that they’re taken to an emergency room.

When a Conversion Reaction involves falling with “LOC,” it’s now called “Psychogenic Non-Epileptic Seizure,” instead of prior less-friendly appellations like “pseudo-seizure” or “hysterical seizure.”  It’s not “faking,” which would be factitious or malingering, in that there’s no conscious control.  Conversion Reactions are entirely involuntary; a mechanism for escaping an unbearable situation.

In my small Appalachia ER, a woman was brought in “comatose,” surrounded by worried family.  Not the first time; we knew her conversion reactions well.  I asked the family [likely triggers] to please step out, and they said, “OK, but don’t stick needles in her.”  Huh?  Apparently the last time this happened, a per diem physician had tried to provoke a pain response [not a good way].  The patient was of course conscious, felt it, told her family after, but the psychogenesis was so strong at the time that she didn’t even react!


Often there are no witnesses.  A patient presents having had an episode of amnesia several days ago.  Maybe they awoke on the floor, maybe not.  But they just don’t remember what happened to them.  This is harder.  Query them very specifically about:

1)      the very last thing they remembered before the episode; and
2)      the first thing they remembered as they came to.
If they awoke on the floor, the differential will be:
  • Syncope
  • Seizure (generalized)
  • TIA (basilar artery)  [rare]
  • Head Trauma (unrecognized)

A patient with sudden LOC from a basilar artery TIA may recall severe vertigo.  Head trauma causing LOC without memory of the blow is possible but highly unlikely.  In terms of psychogenic “collapse,” this wouldn’t occur without people around.

So we’re usually left with Seizure vs. Syncope, & nobody to describe how long it lasted.  The diagnostic approaches are very different.  Syncope is rule-out Cardiac vs. Vasovagal vs. Orthostatic.  Seizure work-up is Neuro.

Obtain clues from the little history you have.  Most important, try to get a sense of time elapsed.  My only suggestion: be a detective!  Question (i.e. interrogate) about the last thing they remembered before, & the first thing afterward.  If the event occurred in a busy public area, it’s unlikely to have lasted more than a few minutes

For example, one of my patients fell in the bathroom.  A family member heard the thud, ran in, & the patient was already awake.  Time here was clearly short.  No tongue bite or incontinence.  Diagnosis — Syncope (probably “micturition syncope,” caused by vasovagal bradycardia from cholinergic stimuli of parasympathetic voiding).

Vasovagal syncope may be caused by:
  • Emotional trigger (fear, pain, disgust, laughter, etc.)
  • Autonomic functions: cough, post-micturition, defecation, swallow (esp. cold liquid)
  • Valsalvas: weight-lifting, horn-playing, etc.
  • Situational: crowded room, prolonged standing, heat
  • Post-prandial, a combo of autonomic function plus circulatory steal (stomach from brain)
Orthostatic syncope may be provoked by:
  • Volume depletion
  • Medications / alcohol
  • Autonomic instability (diabetes, Parkinson’s, etc)
Cardiac syncope is due to Arrhythmias, which may be:
  • Benign: supraventricular tachycardia
  • Life-Threatening: heart block, ventricular tachycardia, long QT
Exertional syncope suggests cardiac by a different mechanism, either:
  • Coronary Artery disease (i.e. angina)
  • Outflow obstruction (hypertrophic cardiomyopathy, tumors, aortic stenosis)
Neck Movement causing syncope may be from either:
  • Carotid sinus pressure (vasovagal)
  • Aberrant carotid artery occlusion (causing a posterior-circulation TIA)

People who faint retain memories up to the point they lose consciousness.  But they don’t remember the fall.  Someone who trips, hits their head, and is knocked out, usually recalls going down (e.g. how they tried to protect themselves).  However, there may be just enough retrograde amnesia from the concussion to forget.

Another patient awoke on the floor by her bed.  Could have been orthostatic syncope, but then she’d have remembered losing consciousness right after getting up.  Her inability to describe a rapid coming-to suggested a longer time course (post-ictal).  Diagnosis — Seizure (which occur disproportionately at night).

Epileptic seizures often have auras which might be recalled.  They include a wide variety of phenomena, depending on the part of the brain where it all began.  Click for a list of possible Auras.

If there was no fall, simply a period of unwitnessed amnesia for less than an hour, the differential is:

  • Complex-Partial Seizure (discussed above)
  • Dissociative State (psychogenic)

I once worked up a friend who’d been working abroad during a civil war, and was having episodes of amnesia.  She visited San Francisco, I ordered an EEG and MRI (both normal).  Neurology said there was no way to distinguish between the 2 conditions, favored the latter since tests were normal & war is tough.  But I knew her situation — not particularly traumatic.  It was only weeks later, before flying to Chicago, that she confided she was about to confront a brother who’d molested her in childhood.  Diagnosis:  Dissociative State.


History rules (!) when determining what caused LOC a few days ago.  Main differentials are:

  • Fell to Floor:   Syncope vs. Seizure (generalized) vs. Conversion Reaction
  • No Fall (witnessed):   Seizure (complex partial) vs. Total Global Amnesia
  • No Fall (unwitnessed)   Seizure (complex partial) vs. Dissociative State

Query witnesses if any, or glean as best you can, about the following key clues:

Fell to (or Awoke on) Floor

Duration of LOC on floor:
  • <20 secs:   Syncope
  • >1 min:   Seizure
  • >5 min:  Conversion Reaction
  • Rapid:  Syncope, Conversion Reaction
  • Post-Ictal gradual transition, confusion to lucid:  Seizure
Pt. can relate what others did during episode
  • Conversion Reaction (i.e. no true LOC)
Movements of  Extremities:
  • Tonic-Clonic:  Seizure (brief jerks possible w/ syncope)
  • Flailing (random):  Conversion Reaction
  • Rolled back:  Seizure, Syncope
  • Nystagmus to just one side:  Seizure
  • Glazed:  Syncope, Seizure
  • Clenched shut:  Conversion Reaction
  • Side of Tongue:  Seizure, ? Syncope
  • Lips, hands etc.:  Conversion Reaction
  • Environmental, Valsalva, Autonomic:   Syncope
  • Exertion:  Cardiac Syncope
  • Neck Movement:  Syncope (vasovagal); TIA (posterior)
  • Situational Stress Present:  Conversion Reaction
Cardiovascular Risk Factors:
  • Syncope from Arrhythmia or Coronary Insufficiency
  • TIA (basilar artery)
  • Seizure always possible anyway
Associated Symptoms recalled by Patient:
  • Aura:  Seizure
  • Vertigo, Diplopia, Dysarthria:  TIA
Cyanosis:  Seizure
Foaming At Mouth:  Seizure
Incontinence:  Seizure

No Fall (witnessed)

Strange Movements:  Complex Partial Seizure
  • grimace, lip-smack, chew, teeth clench, drool, swallow, blink
  • twitch, shake, foot stomp, hand wave, tremor
  • stare, stiffen
  • random walk / run, undress
  • utterances (meaningless sounds)
Patient Recall:
  • Total Amnesia during event:  Complex Partial Seizure
  • Total Loss of Awareness during event:  Complex Partial Seizure
  • Oriented to Person:  Total Global Amnesia
  • Retains past memories during event:  Total Global Amnesia
No Fall (unwitnessed):    Complex Partial Seizure vs. Dissociative State
  • Total Global Amnesia possible
  • Intoxication possible
  • Impossible to distinguish if unwitnessed

Next posting we’ll address the work-up for LOC, whether witnessed or not.

2 responses to “Loss of Consciousness (LOC) – 1

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