Introduction: Transient global amnesia (TGA) is a spontaneously resolving, anterograde amnesia that lasts mostly <24 h and often occurs with retrograde amnesia. The etiology of TGA remains unclear, although in recent decades, many risk factors and preceding events have been identified. There are few up-to-date reports on the TGA incidence in Northern Europe. In this study, we report the incidence and risk factors associated with TGA in Finland. Materials and Methods: The study included all patients with suspected TGA that were referred to Kuopio University Hospital (KUH) in 2017. The hospital catchment area included 246,653 individuals. Risk factors and demographic data were collected from medical records. The TGA incidence rates were calculated as the number of patients with TGA divided by the number of individuals at risk in different age groups. Results: In 2017, 56 patients were treated for TGA at KUH. Of these, 46 had a first-ever TGA. The most common event preceding TGA was physical effort (n = 28, 50%), followed by emotional stress (n = 11, 19.6%) and water contact or a temperature change (n = 11, 19.6%). The most common comorbidities were hypercholesterolemia (n = 22, 39.3%), hypertensive disease (n = 21, 37.5%), hypothyroidism (n = 11, 19.6%), coronary artery disease (n = 8, 14.3%), and migraine (n = 7, 12.5%). TGA occurred most often in December (n = 9, 16.0%), March (n = 8, 14.3%), or October (n = 8, 14.3%), and least often in November and May (n = 2, 3.6% in both months). The crude incidence of a first TGA in Eastern Finland was 18.6/100,000 inhabitants, and when standardized to the European population in 2010, it was 14.3/100,000 inhabitants. Therefore, the TGA incidence was higher than previously reported in European countries. Discussion: The most common precipitating factors for TGA were physical effort, emotional stress, and water contact/temperature change. The incidence of TGA was high in the Eastern Finnish population.

Transient global amnesia (TGA) was first described in 1956 1, 2, and the term TGA was presented by Fisher and Adams in 1964 3. In the review of Arena and Rabinstein (2015), TGA is defined as follows: “Transient global amnesia is a clinical syndrome characterized by the sudden onset of anterograde amnesia, accompanied by repetitive questioning, sometimes with a retrograde component, lasting up to 24 h, and without compromise of other neurologic functions.” 4. TGA typically occurs in people aged 40–80 years and often lasts 1–8 h 5.

The etiology of TGA remains unclear, despite decades of studies. There are several theories about the pathogenesis of TGA, including vascular-, epileptic-, and migraine-related mechanisms 4. The hypothesized underlying vascular mechanisms include a transient ischemic attack (TIA) in the hippocampal area, venous congestion, and cerebral vasoconstriction 5. The theory that hippocampal pathology plays a central role in TGA is supported by the finding that hyperintense hippocampal lesions were found in over 70% of diffusion-weighted magnetic resonance images from patients with TGA 6. The Valsalva maneuver may lead to impaired venous blood reflux; thus, it may induce a TGA attack 7. Furthermore, emotional stress may also evoke a TGA 5 because cortisol levels are reported to be elevated during a TGA 8. In addition, seasonal variations in the TGA incidence have been reported. TGA seems to occur more often during cold weather 9, 10. Quinette et al. 11 suggested that the physiopathology of TGA may be multifactorial. They found 3 different groups of patients with TGAs: men with no medical history, but a physical precipitating factor before a TGA; women with a preceding stressful event; and young patients with migraine.

Migraine was reported to occur more often in patients with TGA than in both healthy controls and patients with TIAs 12. However, patients with TGA were reported to have lower levels of cardiovascular risk factors, compared to patients with TIA, but similar levels to those observed in controls 11, 13.

In previous studies, the TGA incidence has varied, with a range of 2.9–10.4/100,000 inhabitants 14-19. In the Finnish population, the TGA incidence was reported once, 30 years ago, when the annual incidence of a first TGA was 10/100,000, and among people aged over 50 years, it was 32/100,000. In that report, TGAs occurred more frequently in women than in men 19.

The latest reports of the TGA incidence in Northern Europe, including Finland, were published decades ago. Considering the unclear etiology of TGA, more information on its incidence and the risk factors associated with TGA are warranted. In this study, we examined the incidence, the risk factors, and the precipitating events associated with a TGA in Finland.

This retrospective, hospital-based study was carried out in the Northern Savonia area of Eastern Finland. According to Statistics Finland, the population in this area was 246,653 citizens in 2017 20. All patients from Northern Savonia with a suspected TGA were referred to Kuopio University Hospital (KUH). We retrospectively identified patients with the ICD-10 diagnostic code (G45) assigned in the KUH patient data system. Patients were divided into TIA and TGA groups, according to the diagnostic code. Only the TGA group (ICD-10 G45.4) was included in this study. Hospital admissions took place between January 1st and December 31st, 2017.

The delay from the onset of TGA symptoms to hospital arrival was 1–5 h in 90% of patients, varying from 1 h to several days. Diagnostic examinations included a minimum medical examination, physiological measurements, laboratory tests, an ECG, and a head CT or MRI. Electroencephalogram is not included in common examinations of TGA, and none of our patients received an electroencephalogram during the acute phase. TGA diagnoses were identified and confirmed by two study researchers. Data were collected from patient medical records, which included entries made by nurses or doctors, laboratory results, and imaging reports.

The precipitating factors and preceding events were collected and classified into the following categories: emotional stress, physical effort, acute pain, water contact or temperature change, sexual intercourse, and other factors, according to Quinette et al. 11. The water contact and temperature change information was not always directly found in patient records; therefore, the study researchers made some interpretations. For example, a preceding event like “going out in winter” or “leaving the sauna” was recorded as a temperature change. Other factors included events or factors that occurred before TGA but did not meet the criteria of other classifications (for example, sleeping disturbances, medical examinations, a coughing fit, or vomiting/diarrhea). When sleeping disturbances were the preceding factor, they were categorized in the way the patient had described (for example, “had not slept well” or “stayed awake”). When a precipitating factor was not mentioned, we assumed the patient did not have one.

The incidence rates were calculated by dividing the number of patients with TGA by the number of people at risk. Then, it was standardized to the European population in 2010. We calculated 95% confidence intervals with the exact method. The analyses were performed with SPSS versions 26 and 27 (IBM, Armonk, NY, USA).

In 2017, 56 patients referred to KUH had confirmed TGA. Of these, 46 had a first-ever TGA, and ten (17.9%) had a second or third TGA. Every patient with a second or third TGA episode in 2017 had had one or more previous TGA episodes in 2004–2016. In 1 patient, the year when previous TGA occurred was not mentioned.

A head CT was performed for 54 patients, and an MRI was performed for 2 patients. The findings in MRI were normal in both patients to whom MRI was carried out. In 1 patient, MRI was normal during acute event. In another patient, MRI was carried out 5 months after the TGA with normal findings. ECG was taken in all but 1 patient with TGA. One patient had minimal ST-changes in leads V3–V6 and T-inversions in leads III and V1. In that patient, laboratory tests initially revealed a slightly increased TnT level but it decreased to normal in the control sample 2 h later. Another patient had atrial fibrillation in ECG. Sinus bradycardia (HR under 60 BPM) was found in 10 patients. Among these patients, the heart rate varied from 51 to 58 BPM. In addition, 1 patient had a previously diagnosed atrial fibrillation with slow ventricular response rate (59 BPM).

The demographic data of patients with TGAs are shown in Table 1. Among those with first-ever TGAs, 22 were men (47.8%) and 24 women. The mean age of the first-ever TGA group was 64.5 years (62.4 years in men and 66.5 years in women; p = 0.15). The age profile of the first-ever TGA group is presented in Figure 1. The most common comorbidities in the first TGA group were hypertensive disease (n = 16, 34.8%) and hypercholesterolemia (n = 16, 34.8%). Accordingly, antihypertensive medication (n = 19, 41.3%) and statins (n = 14, 30.4%) were the most common previous medications. In our data, 7 patients had a past history of migraine. Two of them had headache during the acute event: in 1 patient the headache was similar as in migraine, while in the other, the headache was nonspecific. One patient with no background of migraine had mild nonspecific headache during the acute event.

Table 1.

Demographic characteristics of patients with transient global amnesia (TGA; N = 56)

CharacteristicFirst-ever TGA (n = 46)Recurrent TGA (n = 10)
Age, years mean ± SD (range) 64.5±9.76 (39–86) 71.5±7.31 (60–79) 
Male 22 (47.8) (50.0) 
Prior TIA (2.2) (10.0) 
Diagnosed hypertensive disease 16 (34.8) (50.0) 
Heart diseases 
 CAD (10.9) (30.0) 
 AF (6.5) (10.0) 
 Former myocardial infarction (0) (0) 
 Aortic valve disease (2.2) (0) 
 Mitral valve disease (0) (0) 
 Cardiac insufficiency (2.2) (0) 
Hypercholesterolemia 16 (34.8) (60.0) 
Migraine (15.2) (0) 
Epilepsy (0) (0) 
Hypothyroidism 10 (21.3) (10.0) 
Asthma (10.9) (10.0) 
Diabetes 
 Type 1 diabetes (0) (0) 
 Type 2 diabetes (6.5) (10.0) 
Medication 
 Antihypertensive medication 19 (41.3) (70.0) 
 Statins 14 (30.4) (50.0) 
 Platelet aggregation inhibitors 12 (26.1) (40.0) 
 Warfarin (6.5) (0) 
 DOAC (4.3) (10.0) 
CharacteristicFirst-ever TGA (n = 46)Recurrent TGA (n = 10)
Age, years mean ± SD (range) 64.5±9.76 (39–86) 71.5±7.31 (60–79) 
Male 22 (47.8) (50.0) 
Prior TIA (2.2) (10.0) 
Diagnosed hypertensive disease 16 (34.8) (50.0) 
Heart diseases 
 CAD (10.9) (30.0) 
 AF (6.5) (10.0) 
 Former myocardial infarction (0) (0) 
 Aortic valve disease (2.2) (0) 
 Mitral valve disease (0) (0) 
 Cardiac insufficiency (2.2) (0) 
Hypercholesterolemia 16 (34.8) (60.0) 
Migraine (15.2) (0) 
Epilepsy (0) (0) 
Hypothyroidism 10 (21.3) (10.0) 
Asthma (10.9) (10.0) 
Diabetes 
 Type 1 diabetes (0) (0) 
 Type 2 diabetes (6.5) (10.0) 
Medication 
 Antihypertensive medication 19 (41.3) (70.0) 
 Statins 14 (30.4) (50.0) 
 Platelet aggregation inhibitors 12 (26.1) (40.0) 
 Warfarin (6.5) (0) 
 DOAC (4.3) (10.0) 

CAD, coronary artery disease; AF, atrial fibrillation; DOAC, direct oral anticoagulants.

Numbers in parentheses are percentages, unless otherwise indicated.

Fig. 1.

Age profiles of patients with first-ever transient global amnesia in 2017.

Fig. 1.

Age profiles of patients with first-ever transient global amnesia in 2017.

Close modal

Among 10 patients (5 men, 5 women) with a recurrent TGA, the mean age was 71.5 years (73 years in men and 70 years in women). In 3 patients, the TGA was the third, and in 7 patients, the TGA was the second. Half of the patients (n = 5, 50%) were diagnosed with hypertensive disease, and 7 (70%) used antihypertensive medications. Six (60%) patients had hypercholesterolemia, and 5 (50%) used statins.

One or more preceding events or risk factors were reported by 71.7% of patients with a first-ever TGA and by 90.0% of patients with recurrent TGA (Table 2). Physical effort was the most common (50%) preceding factor in both groups (n = 23/46 with first-ever TGA and n = 5/10 with recurrent TGA).

Table 2.

Risk factors and precipitating events among patients with transient global amnesia (TGA; N = 56)

Factor/eventFirst-ever TGA (n = 46)Recurrent TGA (n = 10)
Physical effort 23 (50.0) (50.0) 
Emotional stress (19.6) (20.0) 
Water contact or temperature change (17.4) (30.0) 
Pain (10.9) (10.0) 
Sexual intercourse (2.2) (0.0) 
Other factors (13.0) (30.0) 
Factor/eventFirst-ever TGA (n = 46)Recurrent TGA (n = 10)
Physical effort 23 (50.0) (50.0) 
Emotional stress (19.6) (20.0) 
Water contact or temperature change (17.4) (30.0) 
Pain (10.9) (10.0) 
Sexual intercourse (2.2) (0.0) 
Other factors (13.0) (30.0) 

Numbers in parentheses are percentages.

Among 46 patients with first-ever TGA, emotional stress (n = 9, 19.6%) and water contact or temperature change (n = 8, 17.4%) were also common preceding events. Five patients (10.9%) reported pain as the preceding event, mostly headache (n = 3, 6.5%); 6 patients reported sleeplessness (13%) as the preceding event. Among the 10 patients with recurrent TGA, the other common precipitating factors were water contact/temperature change and other factors (coughing, medical examination, or vomiting/diarrhea), both reported by 3 (30.0%) patients.

The incidence of first-ever TGA in Eastern Finland was calculated to be 18.6/100,000 inhabitants. The incidences were 18.0/100,000 in men and 19.3/100,000 in women. When standardized to the European population in 2010, the TGA incidences were 14.3/100,000 in men, 14.1/100, 000 in women, and 14.3/100,000 overall (Table 3).

Table 3.

Age- and sex-specific incidence rates of first-ever transient global amnesia (TGA) per 100,000 inhabitants in Northern Savonia, Finland, in 2017

Age group, yearsMenWomenTotal
NN at riskrate95% CINN at riskrate95% CINN at riskrate95% CI
0–49 68,699 1.46 0.04–8.11 65,181 1.53 0.04–8.55 133,880 1.49 0.18–5.40 
50–54 8,563 35.0 7.22–102 8,243 0.00 0.00–44.8 16,806 17.9 3.68–52.2 
55–59 9,067 55.1 17.9–129 9,036 55.3 18.0–129 10 18,103 55.2 26.5–102 
60–64 9,491 21.0 2.55–76.1 9,428 31.8 6.56–93.0 18,919 26.4 8.58–61.7 
65–69 9,338 64.3 23.6–140 9,387 53.3 17.3–124 11 18,725 58.7 29.3–105 
70–74 6,874 43.6 9.00–128 7,587 79.1 29.0–172 14,461 62.2 28.5–118 
75–79 4,603 43.4 5.26–157 5,768 52.0 10.7–152 10,371 48.2 15.7–113 
80–84 3,030 0.00 0.00–122 4,707 0.00 0.00–78.4 7,737 0.00 0.00–47.7 
≥85 2,364 0.00 0.00–156 5,287 18.9 0.48–105 7,651 13.1 0.33–72.8 
All ages 22 122,029 18.0 11.3–27.3 24 124,624 19.3 12.3–28.7 46 246,653 18.6 13.7–24.9 
ASR   14.3 8.88–22.2   14.1 8.94–21.8   14.3 10.4–19.4 
Age group, yearsMenWomenTotal
NN at riskrate95% CINN at riskrate95% CINN at riskrate95% CI
0–49 68,699 1.46 0.04–8.11 65,181 1.53 0.04–8.55 133,880 1.49 0.18–5.40 
50–54 8,563 35.0 7.22–102 8,243 0.00 0.00–44.8 16,806 17.9 3.68–52.2 
55–59 9,067 55.1 17.9–129 9,036 55.3 18.0–129 10 18,103 55.2 26.5–102 
60–64 9,491 21.0 2.55–76.1 9,428 31.8 6.56–93.0 18,919 26.4 8.58–61.7 
65–69 9,338 64.3 23.6–140 9,387 53.3 17.3–124 11 18,725 58.7 29.3–105 
70–74 6,874 43.6 9.00–128 7,587 79.1 29.0–172 14,461 62.2 28.5–118 
75–79 4,603 43.4 5.26–157 5,768 52.0 10.7–152 10,371 48.2 15.7–113 
80–84 3,030 0.00 0.00–122 4,707 0.00 0.00–78.4 7,737 0.00 0.00–47.7 
≥85 2,364 0.00 0.00–156 5,287 18.9 0.48–105 7,651 13.1 0.33–72.8 
All ages 22 122,029 18.0 11.3–27.3 24 124,624 19.3 12.3–28.7 46 246,653 18.6 13.7–24.9 
ASR   14.3 8.88–22.2   14.1 8.94–21.8   14.3 10.4–19.4 

ASR, age-standardized rates (standardized to the European population of 2010).

95% confidence intervals (CIs) were calculated with exact method.

The seasonal variation in TGA occurrence is shown in Figure 2. The highest TGA occurrence took place in December (n = 9, 16.0%), followed by March and October (n = 8, 14.3% in both months). The lowest TGA occurrences took place in November and in May (n = 2, 3.6% in both months). At the time the TGA occurred, 30 patients (53.6%) were inside a building and 22 (39.3%) were outside. During the diagnostic examination, most patients with TGAs (n = 51, 91.1%) were hypertensive (blood pressure above 140/90 mm Hg).

Fig. 2.

Monthly frequency of transient global amnesia cases in the Finnish population in 2017.

Fig. 2.

Monthly frequency of transient global amnesia cases in the Finnish population in 2017.

Close modal

The present study found that, in Eastern Finland, the estimated crude incidence of TGA was 18.6/100,000 overall, and 14.3/100,000 when standardized to the European population in 2010. Among the precipitating factors that led to TGA, physical effort was the most common, followed by emotional stress and water contact or a temperature change.

We found that comorbidities and medication use were common among patients with TGA. Among all patients with TGA, hypercholesterolemia (39.3%) was the most common previous disease, followed by a hypertensive disease (37.5%), hypothyroidism (19.6%), coronary artery disease (14.3%), and migraine (12.5%). Type 2 diabetes was diagnosed in 7.1% of patients with TGA. Previous studies on patients with TGA reported prevalences of 21.9–60.5% for hypertension or high blood pressure, 20–53% for dyslipidemia or hypercholesterolemia, 0–6.4% for diabetes, and 24% for past history of migraine 11, 17, 21, 22. In a previous review, patients with TGA did not have more cardiovascular risk factors or migraine, compared to controls 11. In our study, patients with TGA had hypercholesterolemia more often than reported in previous studies. In contrast, in our TGA cohort, migraine and hypertensive disease seemed to occur less frequently than previously reported. However, in 34 (60.7%) of our patients with TGA, the blood pressure measured at hospital admission was above 160/100 mm Hg; this result suggested that TGA was a stressful event, but it may also have indicated underdiagnosed hypertension.

In 2017, in the Finnish population over 30 years old, 53% had hypertension, 57% had hypercholesterolemia, and 12% had diabetes. Cardiac insufficiency was diagnosed in 8%, and coronary artery disease was diagnosed in 11% of Finnish individuals over 50 years old 23. In 2017, 5.9% of the Finnish population used levothyroxine for hypothyroidism 24. According to a large population-based study in the USA, approximately every tenth person had experienced migraine 25. According to the present study, cardiovascular diseases and diabetes seemed to be more rare among patients with TGA than in the general Finnish population. Conversely, hypothyroidism and migraine were more common among patients with TGA than in the general population.

In the present study, among all patients with TGA, physical effort (50%) was the most common precipitating event. Emotional stress and water contact or temperature change (both 19.6%) were the next most common events preceding a TGA. Pain was mentioned in 10.7%, and sexual intercourse in 1.8% of cases. In previous studies, the TGA was preceded by physical activity in 22–25%, emotional stress in 20–31%, water contact/temperature change in 4.6–14%, acute pain in 2–3%, and sexual intercourse in 2.6–11% of cases 11, 17, 21, 26. Thus, in our study, physical effort, water contact/temperature change, and pain preceded TGA more often than reported in previous studies. In contrast, emotional stress and sexual intercourse preceded a TGA equally or less frequently than reported in previous studies.

The mean age in the first-ever TGA group was 64.5 years. Women were slightly, but not significantly older than men (66.5 vs. 62.4 years old). Patients with recurrent TGA were older than patients with first-ever TGA (71.5 vs. 64.5 years old). In European reports, the mean age of patients with TGA varied between 61 and 67.3 years 15-19. According to an Italian report, women were significantly older than men at the time of a TGA attack (64.6 vs. 60 years, p < 0.05) 16. In our study, the mean age of patients with a first-ever TGA was among the highest of the mean ages reported for European patients with a first-ever TGA, and higher than the mean age of European patients with recurrent TGA.

In Eastern Finland, in 2017, nearly 18% of patients with TGA had a recurrent event. Previous studies have shown that TGA recurrence rates varied between 2.9 and 23.8% 14, 27, 28. A personal history of migraine, depression, or a previous head injury was suggested to predispose patients to recurrent TGA 21, 28, 29. In our study, cardiovascular risk factors were more common in patients with recurrent TGA than in patients with first-ever TGA. However, that result may be explained by the fact that patients with recurrent TGA were older than patients with first-ever TGA. Among the patients with first-ever TGA, 15% had reported a previous migraine. Conversely, among the patients with recurrent TGA, none reported a migraine. In our study, the recurrence rate was remarkably high.

In this study, the average incidence of first-ever TGA was 14.3/100,000 inhabitants, when standardized to the European population in 2010. We found no significant difference in TGA incidences between the sexes. Similar results were found in a previous meta-analysis 11. In this study, the crude incidence of first-ever TGA was higher than the incidences previously reported 14-19. In our catchment area, most patients with TGA were referred to KUH for a medical examination. In addition, the diagnostic routine included comprehensive examinations for the differential diagnosis; therefore, all TGAs were most likely recognized and recorded.

The Eastern Finnish climate has a notable seasonal variation; in 2017, the outside temperatures ranged from −28.5°C in January to 24.5°C in July 30. In the present study, TGA was diagnosed most often during December, which is one of the coldest winter months in Northern Europe. Our finding that the TGA incidence showed seasonal variation was supported by previous reports, from Italy and Israel, where TGA occurred most often in winter or early spring 9, 10. Many patients experienced the TGA outside, often while exercising or gardening. It is possible that cold weather or a change in temperature, with or without physical effort, may partly explain the high TGA incidence in our population.

Study Strengths and Weaknesses

One strength of this study was that our data were representative of the TGA incidence in the Eastern Finnish population because all the TGA cases that occurred in this specific area were diagnosed and treated at KUH. The main limitation was that, due to the infrequency of TGA, the size of our study population was limited. Moreover, some individuals in the KUH catchment area might have had a TGA event in other hospital districts, and the TGA was not included in this study. Therefore, the reported incidence is minimal rate. However, the incidence rate was slightly higher than in previous studies, which indicated that the study design was appropriate, and most patients with suspected TGA that lived in the KUH catchment area were referred to KUH. Another study strength was that all patients received comprehensive examinations for differential diagnoses, including laboratory tests, an ECG, a medical examination, and a head CT or MRI, before the TGA was diagnosed. All the TGA diagnoses in our study population were confirmed by two study researchers (V.B. and T.K.). Additionally, all the data were collected by one study researcher (V.B.), and specific information was checked by another study researcher (T.K.), which ensured that all the data were processed similarly.

This study found that the most common factors preceding TGA were physical effort, emotional stress, and water contact or a change in temperature. We found that the minimal incidence rate of TGA in Eastern Finland was higher than previously reported in European countries. Due to the remarkable seasonal variation in our outside temperatures, the TGA incidence appeared to be highest in cold weather and in the winter season.

We thank Tuomas Selander for excellent statistical advice.

Ethics Committee permission was waived for this study because in Finland, neither legislation nor the guidelines of the Finnish National Board on Research Integrity (TENK) required ethical review by an Ethics Committee for research based purely on public and published data, registry and documentary data, or archival data. Therefore, written informed consent was not required, decided by the University of Eastern Finland (UEF) Research Ethics Committee in 2021 31.

The authors declare no conflict of interest.

T.K. discloses support for this study from the KUH Research Foundation, Aarne Koskelo Foundation, Antti and Tyyne Soininen Foundation, Maire Taponen Foundation, and Paavo Ilmari Ahvenainen Foundation.

Original study design: A.K. and H.T. V.B. was responsible for the data collection and analyses. A.K., H.T., and T.K. checked the collected data. T.K. reanalyzed specific parts of the data and was mainly responsible for drafting the manuscript. All authors (T.K., V.B., H.T., A.K., P.J.) contributed to data interpretation and analysis and drafting the manuscript.

The data were pseudonymized and included information in which patients might be recognized. Consequently, within the EU data protection law, this study was not allowed to publish the data.

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