Transient global amnesia

Definition/diagnostic criteria Transient global amnesia (TGA) is a neurological disorder characterised by a sudden and temporary loss of the ability to form new memories. During an episode of TGA, patients experience a profound but reversible impairment in their ability to recall recent events, while retaining their overall cognitive function and long-term memory. The diagnostic criteria for TGA include:

• Sudden onset of anterograde amnesia, usually witnessed by an observer.
• Preservation of consciousness and personal identity throughout the episode.
• The absence of other neurological deficits or focal neurological signs.
• Resolution of symptoms within 24 hours.

Epidemiology TGA is a relatively uncommon condition, with an estimated annual incidence rate of 5 to 10 cases per 100,000 population in the United Kingdom. The condition primarily affects individuals aged 50 and older, with a slight predilection for males.

Although the exact cause of TGA remains unclear, it is thought to be associated with various precipitating factors such as emotional stress, physical exertion, Valsalva manoeuvre and exposure to cold water. There is no strong evidence of a genetic predisposition to TGA.

Diagnosis
Clinical features: Patients experiencing TGA typically present with a sudden onset of severe anterograde amnesia, often described as an inability to form new memories. Common clinical features include repetitive questioning, disorientation to time and place, and an anxious demeanour.

It is crucial for GPs to differentiate TGA from other memory disorders, such as transient epileptic amnesia, which may require different management approaches.

Investigations: Diagnosing TGA primarily relies on clinical assessment and exclusion of other potential causes of amnesia. However, investigations may be useful to rule out other conditions and provide reassurance to both the patient and clinician. Commonly employed investigations include:

• Neuroimaging: Typically performed using CT or MRI, is essential to exclude structural abnormalities such as stroke or intracranial haemorrhage. In TGA, these scans typically appear normal.
• ECG: An electrocardiogram (ECG) may be performed to evaluate for any arrhythmias or cardiac abnormalities, as some cases of TGA have been associated with cardiac events.
• Blood tests: Routine blood tests, including full blood count, electrolytes, liver function, and thyroid function, can help exclude metabolic and systemic causes of amnesia.
• Cerebrospinal fluid analysis: Lumbar puncture may be considered in cases with atypical features or when the diagnosis remains uncertain to rule out infection or inflammation of the central nervous system.

Treatment The management of TGA primarily involves reassurance and supportive care.

Prognosis The prognosis for TGA is excellent, with most patients experiencing a complete resolution of symptoms within 24 hours of onset. Recurrence rates are low, estimated at less than 5% per year, and patients who do experience a recurrence often have a similar benign course. Long-term cognitive impairment or neurological sequelae are rare in TGA.