Transient global amnesia (TGA) is a sudden episode of confusion in which an affected individual has sudden memory loss and a period of amnesia which generally lasts from a few minutes to a few hours. A condition usually of older and middle-aged adults, the feeling is stupefying to those it affects. Many people are taken to an emergency room or hospital believing they are suffering from the after-effects of a stroke, but there are no other associated neurological signs, and a complete return to normal (excepting having no recollection of the events that transpired during that time) is the rule.
The condition was first described in 1956 and is often mistaken for a transient ischemic event or a neurologic occurrence such as a mini-stroke. A person will go blank for a short period of time and appear to have acutely lost the ability to understand where he is, what is going on in his surroundings and what happened in the interim from when the amnesia started. He will not understand why he has been taken somewhere for evaluation, have no idea of time when he was acutely aware of it pre-attack, or figure out how he got to the present surrounding environment. The amnesia covers a longer period at first and then is limited to the period of the attack only, as days pass. In the long term, memory is completely preserved except for anything that happened during the time of the episode. It’s not a sudden “where am I” feeling, but more a loss of recollection of any events surrounding the event.
There are diagnostic criteria that must be fulfilled to make the diagnosis of TGA and separate it from something more severe neurologically. The attack has to have been witnessed by someone who was present for the majority of the time. There has to be complete amnesia during the attack, not a partial recollection of what was going on. There can be no acute or associated neurological events such as slurring of speech, inability to move an extremity or anything associated with a neurologic pathway which would be diagnostic of a stroke. The cognitive part has to be limited just to the time of the amnesia period, and full resolution of all the occurrences must be within a 24-hour period, usually less. There can be no history of epilepsy or head trauma around the event, as those two types of events may be confused with things like petit mal seizures or concussive symptoms.
Most people are brought in for testing post TGA, particularly in a first occurrence. Twenty percent of people will have a recurrence, though only a couple of times rather than a regular repetition. Blood testing is unremarkable in TGA. While there may be evidence of some restricted blood flow in the hippocampal area on an MRI, the results of most imaging studies with this are not remarkable. Blood vessel studies in arteries supplying the brain as well as EEG and other neurologic testing are generally normal.
Besides fulfilling the criteria mentioned for transient global ischemia, TGA is most often settled on as a diagnosis when other causes are ruled out. Focal seizures can mimic TGA, but they are generally shorter in duration and more recurrent. Low blood sugar (hypoglycemia), particularly in those on insulin, can have similar findings, but sugar reverses the findings and there is generally an accompanying history of such problems. Stroke and transient ischemic attack are important to differentiate. Those conditions are generally associated with more specific neurologic findings and abnormal imaging such as on an MRI. In addition, the duration of the episode will be longer with some sort of neurologic finding which gradually passes.
Thankfully, transient global amnesia is generally a benign condition, and most people recover fully. Recurrent attacks (more than four or five) have to be studied and another cause has to be sought if TGA is too recurrent. Some younger individuals have migraine equivalents which may mimic TGA symptoms. TGA doesn’t appear to be a forerunner of a stroke. However, studies are underway to see if people who have recurrent TGA do have more rapid progression toward intellectual decline or long term risk of epilepsy. Most cases are taken at standard or preferred issue, particularly in one-time events and when other, more serious disease entities have been ruled out with appropriate testing.
