This condition is a transient loss of memory. It is commoner in middle aged and older people. Typically, the disorder occurs following a physically demanding task (28 %), coitus (6.5%), emotional stress (6.5 %), hot or cold bath / shower (5 %), driving or a medical procedure. In about 50 % (33 – 84%) of cases there is no precipitating factor identified.
The mean amnesia duration is ~ 6 hours although complete recovery of subtle functions may take months. Most episodes do not exceed 10 hours although up to 24 hours has been reported. There is no peripheral neurological deficit. A history of amnesia lasting less than one hour is suspicious of an epileptic disorder.
The memory defect is recognised by the individual. There is complete or partial anterograde amnesia. The patient may not recognise acquaintances but does remember close relatives. There is preservation of ideas and motor skills. Some complex tasks are preserved, such as the ability to drive, but there is cognitive impairment with impaired ability to copy complex figures or to name objects.
The following witnessed criteria support the diagnosis (Caplan 1985 and Hodges and Warlow 1990):
Associated symptoms (headache, nausea, dizziness) and some grade of retrograde amnesia may occur, although these are not required for diagnosis. As previously mentioned, the episode may or may not be associated with some triggering event.
The major differential diagnoses for TGA includes other transient amnesic conditions such as TIA, transient epileptic amnesia (TEA) and psychogenic amnesia. Other conditions that should also be considered include alcohol and other drug intoxication (including prescription and OTC medications), hypoglycaemia, head injury, limbic encephalitis, or a severe exacerbation of depression.
In one study 7 % of patients developed epilepsy, all within 12 months. In another study 4.5 % had recurrences of seizures which disappeared with antiepileptic medication. It is thought that in some people epilepsy may be the cause of the transient amnesia. Thus an accurate diagnosis is necessary. It is useful to obtain an EEG early together with cerebral imaging. This should involve a neurologist and investigations. Exclusion of epilepsy and TIA is paramount if the pilot is to ever fly again.
The majority of TGA studies report a significant association with migraine headaches especially in younger individuals. Family and personal history of psychiatric diseases, anxiety, depression, alcohol use, and certain phobic personality traits also have been associated with TGA.
TGA has a significant recurrence rate but there are no predictors for this. The table below is from a 2018 FAA review of TGA. The aggregated data suggest an annual rate of recurrence in the vicinity of 2.5 – 6 % per annum.
| Study | Patients in study (n) | Recurrence | Annual recurrence rate | Mean follow-up |
|---|---|---|---|---|
| Hinge et al., 1986 | 74 | 22% | 4.7% | 66.6 months |
| Miller et al., 1987 | 277 | 14.4%* | 80 months | |
| Hodges and Warlow, 1990 |
114 | 7.9% | 3% | - |
| Melo et al., 1992 | 48 | 6.25% | 17.4 months | |
| Gandolfo et al., 1992 | 102 | 18.63% | 82.2 months | |
| Zorzon et al., 1995 | 64 | 9.4% | 2.5% | 45.6 months |
| Lauria et al., 1997 | 77 | 8.2% | - | |
| Chen et al., 1999 | 28 | 18% | 42 months | |
| Pantoni et al., 2005 | 51 | 8% | 6.8 years | |
| Quinette et al., 2006 | 142 | 3.5% | 5.8% | - |
| Quientte et al., 2006 ** | 1259** | 10.19% | - | |
| Agosti et al., 2006 | 85 | 14.11% | 3 years*** | |
| Arena et al., 2017 | 221 | 5.4% | 4.21 years |
* Included "probable episodes of TGA" recurrence of 23.8%
**Report based on author's literature review.
***Retrospective study where patients were recruited over a 3-year period.
- No data available.
CAA UK and FAA report a low risk of recurrence is pilots who have been returned to flying following a first TGA episode.
If an applicant with TGA presents with a recurrent episode there should be a careful review to ensure that the initial diagnosis was correct.
A pilot suffering from TGA during flight may possibly be able to continue piloting the aircraft and land, if flying day VFR in a known area, with well-known features available for orientation.
But on the other hand, TGA may result in disastrous consequences. When flying on instrument or by night, the complex cognitive functions required, and the lack of available orientation features make it unlikely that a pilot affected by TGA will be able to navigate the aircraft back to safety.
On the first occasions that an applicant presents with a history of Transient Global Amnesia:
An applicant who first presents with a history of TGA should be considered as having a condition that is of aeromedical significance.
A favourable AMC may allow a return to flying, usually with operational restrictions if:
An applicant who subsequently presents with a history of TGA may be considered as having a condition that is not of aeromedical significance if:
