Transient global amnesia

The signs and symptoms of tansient global amnesia (TGA) have been clearly defined by the medical community:^[1][3][4]

• The main sign of TGA is being temporarily unable to form new memories. This is called prominent anterograde amnesia. During the episode of TGA, the person will seem disoriented in time and often ask questions about the date or their environment over and over again. This may be described as the person sounding like a "broken record." 
• During the TGA episode, the person may forget memories from the recent past (retrograde amnesia). The period of memory loss varies and may extend back hours to days or weeks, but only in rare instances, years.
• Other cognitive functions (ability to think) are not affected. In other words, even during the TGA episode, the person will know who they are and will be able to recognize and name familiar objects and people. The person is able to perform normal complex daily tasks such as driving or cooking.
• No other neurological problems are noticed during an exam. For example, reflexes, balance and coordination are normal.
• The TGA episode lasts between 1 and 10 hours (6 hours is the average). When the episode is over, the person will be able to make new memories again, but there will be no memories from the time during the episode. 
• Within 24 hours of the end of the TGA episode, any memories from the past lost during the episode will completely return. This does not include the time during the episode when no new memories could be made. In rare cases, some people may not remember an additional short period of time just before the TGA episode. 
• Other less common symptoms include headache, nausea, dizziness, anxiety, and feelings of tingling and numbness in hands, feet, arms or legs.

There is currently no consensus on an underlying cause of transient global amnesia (TGA). Possible mechanisms that have been proposed include:^[2][4]

• A vascular etiology, such as venous flow abnormalities
• Hypoxia (deficiency of oxygen supply) and/or ischemia (deficiency of blood supply)
• A relation to migraine (some studies have shown that history of migraine is associated with TGA)
• Epilepsy
• Psychological factors

However, none of these theories clearly and consistently explain the features of TGA.^[4] Because no one theory appears to apply to all people with TGA, some speculate that TGA may have multiple different causes.^[4]

Events that reportedly may trigger an episode of TGA include:^[2][5]

• Sudden immersion in cold or hot water
• Physical exertion
• Emotional distress or psychological stress
• Pain
• Medical procedures
• Head trauma
• Sexual intercourse
• A Valsalva maneuver

There is a distinct form of TGA that may occur following excessive alcohol consumption, large sedative doses of barbiturates, the use of several illicit drugs, or sometimes, relatively small doses of benzodiazepines.^[2]

Transient global amnesia (TGA) is considered a sporadic disorder (not inherited, occurring in only one person in a family). However, familial cases of TGA have rarely been reported.^[6] Most familial reports have involved siblings, with only occasional or possible parental involvement. While details of these cases have been incomplete, several of the affected people in these families had a history of migraine.^[6]

Some clinicians believe that TGA can be a manifestation of a migraine aura, in which a familial predisposition to TGA may not be surprising. It is also possible that other genetically-influenced developmental factors might predispose only certain families. On the other hand, rare familial cases of TGA could possibly be coincidental.^[6]

The underlying cause of TGA is largely unknown, and additional published reports of familial cases are needed to investigate a possible genetic component of the disorder.

There is no specific treatment for transient global amnesia (TGA). Fortunately, this condition resolves on its own, typically within hours of onset.^[1] Most people with TGA do not experience repeat episodes.^[1][5]

People with repeat episodes of TGA should document the circumstances triggering the event. For some, it may be possible to prevent TGA by avoiding triggers. However, for many this is not possible. Possible triggers of TGA include:^[5][7]

• Sudden immersion in cold or hot water
• Strenuous physical activity
• Sexual intercourse
• Medical procedures, such as angiography or endoscopy
• Mild head trauma
• Acute emotional distress (e.g., from bad news, conflict or being overworked)
• Exposure to high altitudes

Much of what we know about treatment of recurrent TGA comes from single case reports. These reports emphasize the need to rule out all other possible causes of recurrent TGA type episodes, such as transient epileptic amnesia, vascular disease, heart conditions, and adverse drug events, as this will affect treatment.^{[8][9][10][11]}

The cause of transient global amnesia is not known, but migraines seem to be associated in many cases. We found a single report of metoprolol use for treatment of recurrent TGA in a man with a history of migraine.^[7]

The characteristic symptoms of transient global amnesia (TGA) resolve on their own within 24 hours.^[4] Non-cognitive functions are not affected. Therefore, the presence of other symptoms such as aphasia (impaired ability to communicate); hemiparesis; sensory loss; or incoordination indicates that other possible diagnoses should be explored.^[12]

While TGA is generally considered a "benign" condition, a few studies have looked at the long-term outcome regarding the risk of recurrence and the incidence of cognitive decline, stroke, and seizures over time.^[12] TGA does not seem to be associated with an increased risk of ischemic stroke or seizures. Several studies have reported complete recovery of cognitive function 5 days to 6 months after the TGA episode. However, other researchers have noted that memory dysfunction may persist after the acute phase of the TGA episode, even when patients seem clinically normal or have no awareness of any impairment.^[12] Recurrence rates of TGA range from 2.9% to 26.3%.^[4]