Transient Global Amnesia

Recently, I was taking care of an elderly female who presented to the ED with isolated amnesia. I thought of some rare stroke syndrome until she was seen by a Neurology attending who called it "Transient Global Amnesia". I was not even aware of this diagnostic entity. 

What is Transient Global Amnesia (TGA)?

Transient global amnesia (TGA) is syndrome characterised by the acute onset of anterograde or retrograde amnesia that can last up to 24 hours in the absence
 of other neurologic deficits. TGA exhibits isolated loss of new memory formation limited to facts and events and patients retain motor tasks and coordination. The classic TGA patient asks the same questions repeatedly in the absence of other signs or symptoms. However, symptoms resolve gradually and spontaneously within 24 hours without the need for medical intervention. The definitive diagnosis of TGA cannot be made until symptoms have resolved. 

How does TGA present?
The classic TGA patient asks the same questions repeatedly in the absence of other signs or symptoms. They exhibit anterograde memory loss. For instance, a patient might repeatedly ask "Have we met before" despite several introductions. Other common concurrent symptoms seen with TGA are headache, nausea, and vomiting. 

What are they key points to cover while examining a suspected TGA?
Do a full neurological exam (Cranial Nerves, Sensory-Motor, Cerebellum, Reflexes). Memory function forms a crucial part of the examination as patients with TGA experience explicit memory loss i.e only the loss of memory pertaining to new facts and events (mainly stored by the hippocampus). By contrast, implicit memories (stored in the cerebellum and the basal ganglia) should not be compromised. For example, a TGA patient retains the ability to operate a car or the ability to open a door with a key. Patients also retain all other cognitive functions. 

1. Test immediate versus delayed recall. Immediate recall remains intact in TGA patients, while delayed recall (after 5 minutes) is impaired.

2. Assess attention span. Executive function abilities such as “serial 7s” or spelling the word “world” backwards remains intact during TGA.

3. Test procedural memory. TGA patients retain task memory (eg, making a paper airplane).

4. MMSE

What is the diagnostic criterion for TGA?

1. Witnessed at onset and during attack
2. Must have anterograde amnesia

3. No focal neurological symptoms or signs during or after

4. No epileptic features
5. No clouding of consciousness, no loss of personal identity, and no cognitive impairment other than amnesia

6. No head injury in the past 72 hours

7. No seizures in the last 2 years, and not on medication for epilepsy
8. Must resolve in 24 hours

Differentials for TGA

• Seizure/transient epileptic amnesia 
(lasts < 1 hour)
• Stroke (rarely presents as isolated amnesia) 

• Atypical migraine 

• Head injury/occult trauma/concussion syndrome 
(Manage as Head Injury)
• Medication and recreational drug side effect 

• Herpetic encephalitis 
(fails to resolve in <24hrs)
• Early neurosyphilis 

• HIV dementia 

• Alcohol psychosis 
• Alcohol blackout 


TGA cannot be definitely diagnosed unless and until all symptoms have resolved in under 24 hours. 

What are the risk factors for TGA?

• Past history of TGA
• Advanced Age
• Migraneous Headaches

Diagnostic Tests

The yield of extensive diagnostic testing in search of occult etiologies is low if history is not concerning and examination is normal. However, certain high-risk patients require extensive workup. Imaging is warranted only if examination is concerning  and when the duration of symptoms approaching 24 hours without resolution of symptoms. MRI is preferred over CT whenever possible to rule out an unusual neurological syndromes. If there is any suspicion of an acute ischemic stroke, immediate computed tomography (CT) should be obtained. EEG can be done to rule in seizures.

Any patient with suspects TGA that does not resolve in 24 hours requires a broader investigation (MRI/CT, LP, EEG), admission, and neurologic consultation.

Who needs a extensive work up?

• Absence of witness at onset
• Patients aged < 50 years warrant special consideration, as TGA is rare in young individuals
• High risk - Immunocompromised, Age<50, drugs/alcohol use, Abnormal Vital Signs

Treatment

• Administer Thiamine if there is h/o chronic alcoholism
• Hold medications that may explain amnestic symptoms (BZDs)
• Admit in ED Observation unit or as an in-patient for 1-2 days and watch until resolution of symptoms
• Mainstay of Rx is serial neuro examinations until the patient returns to baseline
• Neurology Consultation 

Most TGA syndromes resolve in < 10 hours. Patients should be observed until symptoms clear. Patients with presumed TGA do not have decisional capacity and therefore must not be permitted to be discharged against medical advice while symptoms are present.

Take Home:

• TGA is characterised by the acute onset of amnesia that can last up to 24 hours in the absence
 of other neurologic deficits. Symptoms resolve gradually and spontaneously within 24 hours without the need for medical intervention. 
• The definitive diagnosis of TGA cannot be made until symptoms have resolved. 
• For a classic case, do minimum tests but pay special attention  to high-risk individuals as well as any patient with abnormal vital signs or unusual symptoms.

References:

1. Faust JS, Nemes A. Transient Global Amnesia: Emergency Department Evaluation And Management. Emergency medicine practice. 2016 Aug;18(6):1.
2. Hodges JR, Warlow CP. Syndromes of transient amnesia: towards a classi cation. A study of 153 cases. J Neurol Neu- rosurg Psychiatry. 1990;53(10):834-843.
3. Hodges JR, Ward CD. Observations during transient global amnesia. A behavioural and neuropsychological study of ve cases. Brain. 1989;112 (Pt 3):595-620.
4. Brown J. ED evaluation of transient global amnesia. Ann Emerg Med. 1997;30(4):522-526. 
5. Quinette P, Guillery-Girard B, Dayan J, et al. What does transient global amnesia really mean? Review of the litera- ture and thorough study of 142 cases. Brain. 2006;129(Pt 7):1640-1658.
6. The transient global amnesia syndrome. JAMA. 1966;198(7):778-779. 

Posted by:

              

     Lakshay Chanana

     

     Speciality Doctor

     Northwick Park Hospital

     Department of Emergency Medicine

     England

     @EMDidactic