Loss of Consciousness (LOC) – 2

Last posting we discussed what to inquire about when a patient presents sometime after an episode of loss of consciousness.  Maybe they fell to the floor, maybe not.  Maybe it was witnessed, maybe not.  Physical exam (cardiac & neuro) are invariably normal.  Our possible causes:

History of Loss of Consciousness  —  Differential Diagnosis

Fell to Floor

Amnesia (without Fall)

As noted in our last posting (LOC-1), we distinguish among the above possibilities by history alone.  Our working diagnosis then defines the tests we order.

Fell To Floor (or Awoke on Floor)

SYNCOPE  —  Suppose we conclude from history that a patient most likely fainted.  As we noted last posting, Syncope can be Vasovagal, Cardiac, Orthostatic, or Neurovascular.

Vasovagal Syncope, the most common etiology, comes to mind if there’s a clear history (e.g. fainted at sight of blood).  Further testing is not necessary.  As noted last post, typical stimuli include:

  • Emotional triggers (fear, pain, disgust, laughter, etc.)
  • Autonomic functions: cough, post-micturition, defecation, swallow (esp. cold liquid)
  • Valsalvas: weight-lifting, horn-playing
  • Situational: crowded room, prolonged standing, heat
  • Post-prandial, a combo of autonomic function plus circulatory steal (stomach from brain)

Persons with vasovagal syncope usually have a brief prodrome, such as feeling dizzy, warm, nausea, or diaphoresis.  In contrast, persons who faint due to cardiac arrhythmia do so without any warning.

Orthostatic Syncope is also diagnosed by history, i.e. faint upon abrupt standing.  If there’s an obvious explanation, like the patient was volume depleted (gastroenteritis), or taking a new medication with likely side effect, additional work-up can also be obviated.

Cardiac Syncope can be due to coronary artery disease (CAD), fixed outflow obstruction, or spontaneous arrhythmias.  The first two are the most imminently dangerous.  Consider them if you note:

  • Family History of early sudden cardiac death (outflow obstruction)
  • Exertional syncope (CAD; outflow obstruction)
  • Cardiac Risk Factors (CAD; outflow obstruction, arrhythmias)
  • Valvular murmurs on exam (outflow obstruction)

Obtain an EKG for all patients with unexplained syncope.  The chance of finding a culprit arrhythmia other than a long or short QT interval is miniscule.  However, key abnormalities may include:

  • Suggestions of coronary artery disease (unlikely present)
  • Signs of structural heart disease (LBBB, LVH)
Obtain an Echocardiogram to r/o outflow obstruction if:
  • Family Hx early sudden cardiac death
  • Murmurs on exam
  • Cardiac Risk Factors
  • EKG suggestive of structural cardiac disease
  • Exertional syncope (esp. if young patient)
Obtain a Stress Test if:
  • Exertional syncope (esp. if coronary risk factors)
  • See posting Chest Pain -1 re: types of stress tests

If you think coronary artery disease is a possibility, begin treatment with aspirin & atorvastatin 80 mg qPM pending work-up.  If you suspect outflow obstruction, prohibit exercise until the echocardiogram is done.

Neurovascular Syncope is due to vertebrobasilar insufficiency, either from TIA due to cerebrovascular disease, or the rare case of aberrant anatomy causing vertebral artery compression with neck movement.

Obtain an MRI-Angiogram or CT-Angiogram of Head & Neck if:
  • Associated Sx of vertigo, diplopia, dysarthria, or dysphagia
  • Syncope due to turning head

Note that an MRI isn’t sufficient.  Order it if you think a patient had a completed CVA, even a mild one.  But to discern risk of future major stroke, you need the non-invasive venous angiogram for vessel stenoses.

None of Above

Well, the syncope had to be something, just may be hard / impossible to tell by history.  For a patient with syncope occurring out of the blue, without clear explanation, the likely causes are:

  • Vasovagal
  • Arrhythmia

If it’s an arrhythmia, it might be either:

  • Benign: Supraventricular Tachycardia (common)
  • Life-Threatening: Heart Block, Ventricular Tachycardia

SVT’s cause syncope at the onset, so inquiring about palpitations may not help.  Arrhythmias can only be detected by ambulatory EKG monitoring, which can be done in various ways, all problematic:

  • Holter Monitor (24-48 hrs):  very low yield
  • Event Monitor (30 days):  patient has to push a button during symptoms, which is essentially impossible for someone who faints
  • Implantable Loop Recorder (ILR):  best of all, but invasive

If completely spontaneous syncope occurs only once, settle for an EKG alone.  If it occurs 2 times in close proximity, or 3 times with still no clear explanation, you’ll probably be headed for an ILR.  Refer to Cardiology if the baseline EKG shows abnormalities like long or short QT, short PR, or LBBB.

Tilt Table Testing: what’s this?  A device in which a patient is strapped to a table & abruptly raised from supine to upright & held there (maybe >30 minutes).  If positive, it diagnoses vasovagal syncope.  Problem is that sensitivity, specificity & accuracy are all low.  I’ve never seen it ordered, much less ever requested it.

It might be useful for the older patient with cardiac risks but a completely negative cardiac work-up, where you wanted some reassurance that frequent syncopal episodes were in fact vasovagal.  Other indications include frequent unexplained falls, to prove tonic-clonic movements are in fact from faints, & syncope in a person with a high-risk occupation (pilot, acrobat, etc.).

SEIZURE  —  We suspect this based on witness accounts (see prior post LOC – 1).  If the patient was alone, we surmise a possible generalized seizure based on the degree of amnesia.  A patient who seized might recall an aura, nothing else.  The vaguer the account, the more time you suspect may have elapsed from start to end, the more reason to suspect a seizure.  Report of a bitten tongue or incontinence is also suggestive.

If “seizure” is your working diagnosis:
  • Order an MRI
  • Order a sleep-deprived EEG
  • Order a CBC, Chemistry panel
  • Arrange a Neurology consultation

The purpose of the MRI is to rule out a causative lesion, e.g. tumor.  A CT, while adequate for masses large enough to cause “headache,” won’t do for the tiny ones that can provoke seizures.  The EEG is to rule in seizure.  Neuro can then put it all together, make a formal diagnosis, & determine management (it’ll be much easier for them if they have the tests ahead of time).

TIA (Basilar Artery)  —  TIA’s are a rare cause of abrupt, brief LOC.  Suspect one if the patient reports severe vertigo preceding the LOC, or if they have had prior episodes of posterior circulation symptoms such as vertigo, diplopia, dysarthria, dysphagia, ataxia, visual field loss, contralateral facial/body numbness.  We could also say to worry in persons with risk factors for Stroke, but those same people would have risks for Cardiac Syncope, which is much more common than basilar artery TIA.

However, if you truly think a person may have lost consciousness due to a TIA, act quick before they have a full-fledged stroke.  An MRI will only identify the latter, NOT the TIA!!!  To look for sources of TIA, order:

  • CT-Angiogram (CTA) or MR-Angiogram (MRA), of both Head and also Neck.  If you only request “brain,” you’ll miss key vertebral artery stenosis
  • Maybe an Echocardiogram for cardiac emboli (Transthoracic good enough; maybe an invasive TTE if everything else negative & suspicion high)

Give aspirin while work-up in progress.  To repeat, acute LOC due to basilar artery TIA would be really rare.

OTHER  —  Suppose a person fell in a way that sounds like a Conversion Reaction: e.g. stressful life situation, random flailing of arms & legs, bit lips, clenched eyes shut, recovered without a post-ictal phase, & was able to describe something about what others around did during the event.  Episodes may be frequent, sometimes daily, at least weekly.

Of course, you may well think it’s psychogenic, but the patient and family won’t be convinced or pleased.  If I’m unable to successfully reassure, rather than order a lot of tests, I refer to Neurology.  Neuro is used to this (25% to 40% of patients who get EEG + videotape for diagnosis are found to have psychogenic nonepileptic “seizures”).

LOC (episode of Amnesia) Without Falling

Here the differential is between Complex Partial Seizure and Dissociative State.  Transient Global Amnesia (TGA) usually lasts long enough to attract attention, resulting in an ER visit.

There’s no way to distinguish among these conditions when a person reports episodes of amnesia.  But it’s essential to identify organic seizures, because 1) treatment is readily available; and 2) there may be an underlying lesion.  So I routinely order both MRI and EEG.

Then I send to Neurology, even if personal or social situations exist that might predispose to psychogenic episodes.  EEGs are sensitive for generalized epilepsy (“grand mal”), but not as much for complex partial.  Sometimes abnormalities are only detected by electrodes inserted in the temporal lobe [!!!].  But Neuro can figure out how far to pursue a possible seizure disorder, and whether to refer to Psych.  If you at least obtain a normal MRI, there’s no tumor responsible.


A person experienced recent LOC & has now recovered.  Maybe they fell to floor, or awoke on it.  Maybe they experienced a period of unwitnessed amnesia.  Exam is completely normal.  You obtain whatever history possible.

If Fell to (or Awoke on) Floor

1.  If you suspect Syncope:
  • Hx suggests vasovagal or orthostatic syncope  →   no tests
  • Exertional Syncope   →   EKG, Echocardiogram, ? Stress Test
  • Completely spontaneous syncope   →   EKG
    • Implantable Loop Recorder if recurrent faints
    • Cardiology referral if abnormal EKG
  • Send to ER if:
    • Same-day exertional syncope
    • Same-day spontaneous syncope + abnormal EKG / cardiac risks
2.  If you suspect Seizure:
  • MRI
  • EEG (sleep-deprived)
  • Neurology referral
3.  If you suspect rare basilar artery TIA:
  • MRA / CTA of Head and Neck
4.  If you suspect Psychogenic “Seizures” [& pt./family insist on “tests”]
  • Refer to Neuro for decisions re: work-up

If Episode of Amnesia (Without a Fall to Floor)

Can’t distinguish among diagnoses by history (unless Dx “intoxication”):
  • MRI
  • EEG (sleep-deprived)
  • Neurology referral

And that’s it for patients presenting with history of LOC.  Hope you haven’t lost consciousness reading all this.

One response to “Loss of Consciousness (LOC) – 2

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