Basics
Description
- Transient global amnesia (TGA) has the following features:
- Episode of amnesia with abrupt onset
- No focal neurologic signs or symptoms
- Temporary, severe, anterograde amnesia:
- Acute inability to form new memories
- Permanent memory gap after the episode
- Temporary short-range retrograde amnesia:
- More recent memories at more risk
- Previously encoded memories unavailable only temporarily
- Gradually improves until only remaining memory deficit is the gap induced by the anterograde amnesia
- Incidence between 3 and 8 per 100,000 people:
- 75% occur in people of 50 " 70 yr old
- TGA rare <40 yr
- Most attacks last between 1 and 8 hr (range 15 min " 7 days)
Etiology
- Multimodal MRI, SPECT, and PET have shown some abnormalities of regional blood flow in selectively vulnerable hippocampal structures
- The exact etiology of TGA is unknown; speculation is controversial
- Speculated causes:
- Vasoconstriction due to hyperventilation:
- Psychogenic hyperventilation in setting of age-related cerebrovascular autoregulatory dysfunction
- Hippocampal venous congestion with Valsalva:
- Ultrasonography has suggested internal jugular vein incompetence
- Migraine (in younger patients)
- No correlation between TGA and thromboembolic cerebrovascular disease has been found
Diagnosis
Signs and Symptoms
Diagnostic criteria:
- Attack must be witnessed
- Acute onset of anterograde amnesia
- No alteration in consciousness
- No cognitive impairment except amnesia
- No loss of personal information (e.g., name, birth date, address, etc.)
- No focal neurologic symptoms
- No epileptic features
- No recent history of head trauma or seizures
- Attack must resolve within 24 hr
- Other causes of amnesia excluded
History
- Often precipitated by stressful condition:
- Cough, Valsalva
- Physical exertion
- Sexual intercourse
- Extreme fright or shock
- Intense heat or cold
- Patient will likely feel something is wrong:
- May ask "how did I get here? "
- May be repetitive in questions
- Will be generally aware of attack
- May have other subtle transient symptoms at onset, such as headache, dizziness, nausea
- Historical features helpful in excluding other diagnoses are:
- Onset of attack witnessed, with no seizure activity or epileptiform features noted
- No history of seizures in prior 2 mo
- No history of recent traumatic brain injury
- Acute anterograde amnesia with relatively preserved remote memory
Physical Exam
- Marked anterograde amnesia
- Most cases ( ≥90% in case series) will demonstrate repetitive questioning
- Neurologic and general exam normal
- TGA patient WILL NOT be:
- Somnolent
- Inattentive
- Globally confused
- Confabulate
- TGA patient WILL be:
- Oriented to name, birth date, address, phone number, date
- Able to perform complex tasks and following complex commands
- Aphasia, apraxia, and agnosia are NOT findings consistent with TGA
Essential Workup
- True TGA can be diagnosed with a careful history and physical exam alone
- If clinical diagnosis is certain, no other workup is essential
Diagnosis Tests & Interpretation
Testing indicated only when the diagnosis is uncertain
Lab
- CBC, comprehensive chemistries including glucose, LFTs, NH3, thyroid studies, and UA for organic " metabolic etiologies were implicated
- Tox screen, alcohol level for toxic etiologies were suspected
Imaging
- Consider MRI if indicated.
- In true TGA, MRI may show a focal hippocampal DWI or T2 lesion that resolves over time
- Head CT for intracranial mass if indicated
Diagnostic Procedures/Surgery
- EEG for seizure or nonconvulsive status if suspected
- Lumbar puncture and CSF analysis for encephalitis if suspected
Differential Diagnosis
- Other entities may present somewhat similarly but will likely have historical or physical exam features that readily distinguish them from TGA:
- Anterior choroidal artery or posterior cerebral artery or TIA:
- Additional related neurologic signs such as hemianopia
- Acute confusional state/Korsakoff syndrome/metabolic disorder:
- Alcohol, medication, or toxin ingestion
- Decreased attention or other findings of an encephalopathy
- Impairment with serial 7s or spelling "world " backward
- Able to lay down new memory if allowed time to encode
- Complex partial seizures/epileptic amnestic attacks:
- Witnessed epileptiform activity or features (e.g., blank stares, automatisms, lip-smacking, olfactory hallucinations)
- Short duration (typically <30 min; TGA lasts hours)
- No repetitive questioning
- Frequent and rapid recurrences
- Psychogenic amnesia:
- Younger patient with a known psychiatric stressor
- Prominent retrograde amnesia
- Psychogenic memory loss for personal identification, name, birth date, etc.
- Temporal lobe brain lesion or encephalitis affecting the temporal lobe:
- Has other associated neurologic symptoms (e.g., visual field cut, confusion)
- Progressive and permanent amnesia
- Previously unrecognized Alzheimer dementia:
- Memory loss for personal information such as date, phone number, address
- Signs of additional global cognitive impairment
Treatment
Pre-Hospital
There are no considerations in true TGA that are specific to the pre-hospital environment
Initial Stabilization/Therapy
There is no known effective therapy for TGA
Ed Treatment/Procedures
- TGA is a self-limited, relatively benign entity
- Observe the patient for improvement
- Assuming a true diagnosis of TGA, no acute treatment beyond reassurance of patient and family is indicated
Medication
First Line
Not applicable
Second Line
Not applicable
Follow-Up
Disposition
Admission Criteria
- Admission for further observation for patients without significant improvement at the time of disposition
- Patients with uncertain diagnosis
- Patients showing a trend toward resolution but who have suboptimal social support at home
Discharge Criteria
- A clear diagnosis of TGA
- Resolving or resolved amnesia
- Good social support
Issues for Referral
- Recurrence rate of TGA is 8%
- Refer patients with recurrent episodes of TGA to a neurologist:
- May benefit from ambulatory EEG to workup epilepsy
Followup Recommendations
Given median age of TGA patients (60 yr), follow-up with primary care provider for general cardiovascular risk factor modification may be beneficial:
- No follow-up specific to TGA is indicated
- See "Issues for Referral " for patient with recurrent episode of TGA
Pearls and Pitfalls
- TGA is a distinct and relatively benign entity:
- Acute onset of isolated anterograde amnesia
- Resolves spontaneously
- Be aware of subtle features that may suggest a more pathologic alternative diagnosis:
- Short, recurrent episodes or automatisms in epilepsy
- Cognitive impairment with encephalopathy
- Subtle neurologic signs in encephalitis or TIA
- If there is uncertainty regarding the diagnosis, the highest yield tests are multimodal MRI and EEG
Additional Reading
- Bartsch T, Deuschl G. Transient global amnesia: Functional anatomy and clinical implications. Lancet Neurol. 2010;9:205 " 214.
- Hunter G. Transient global amnesia. Neurol Clin. 2011;29:1045 " 1054.
- Kirshner HS. Transient global amnesia: A brief review and update. Curr Neurol Neurosci Rep. 2011;11:578 " 582.
- Markowitsch HJ, Staniloiu A. Amnesic disorders. Lancet. 2012;380:1429 " 1440.
See Also (Topic, Algorithm, Electronic Media Element)
Codes
ICD9
- 437.7 Transient global amnesia
- 780.93 Memory loss
ICD10
- G45.4 Transient global amnesia
- R41.1 Anterograde amnesia
- R41.2 Retrograde amnesia
SNOMED
- 230736007 Transient global amnesia
- 88822006 Anterograde amnesia (finding)
- 51921000 Retrograde amnesia (finding)