Acta Neurol Belg DOI 10.1007/s13760-014-0281-3
ORIGINAL ARTICLE
Incidence of transient global amnesia in Merano, province of Bolzano, Italy Francesco Brigo • Piergiorgio Lochner Frediano Tezzon • Raffaele Nardone
•
Received: 8 January 2014 / Accepted: 22 January 2014 Ó Belgian Neurological Society 2014
Abstract Few community-based studies determined the incidence of transient global amnesia (TGA), with annual incidence rates between 2.9 and 10.4/100,000. Data on sex distribution of TGA are discrepant. Aim of this study was to determine the incidence of TGA in Merano, province of Bolzano, Northern Italy. Cases were identified from hospital discharge diagnoses of all the Departments of the general hospital of Merano and neighboring towns. Patients fulfilling internationally accepted diagnostic criteria for TGA and residing in Merano were included. Crude, age- and sex-specific incidence rates were computed. The overall annual crude incidence rate of TGA was 9.6/100,000 inhabitants (9.5 % confidence interval 6.7–13.3), 10.1/100,000 for men and 8.9/100,000 for women (p \ 0.001). After adjustment by the direct method to the European population, the annual incidence rate was 6.4/100,000. The incidence rate of TGA in Merano, Italy, does not differ from that reported in Turku, Finland and Belluno, Italy. This study confirms that this benign syndrome is relatively common and occurs mainly in elderly patients. However, the higher male predominance in TGA incidence rates contrasts with previous epidemiological studies. Further, prospective incidence F. Brigo (&) Section of Clinical Neurology, Department of Neurological and Movement Sciences, University of Verona, Piazzale L.A. Scuro, 10, 37134 Verona, Italy e-mail: [email protected] F. Brigo P. Lochner F. Tezzon R. Nardone Department of Neurology, Franz Tappeiner Hospital, Merano, Italy R. Nardone Department of Neurology, Christian Doppler Klinik, Paracelsus Medical University, Salzburg, Austria
studies should therefore be conducted to further clarify sex predominance in TGA. Keywords Epidemiology Incidence Italy Transient global amnesia
Introduction Transient global amnesia (TGA) is a benign neurological syndrome characterized by the sudden onset of anterograde amnesia usually associated with repetitive questioning [1– 3]. During the event, consciousness, vigilance, immediate memory, personal identity, and all other cognitive functions are typically intact. Symptoms resolve within a few hours, by definition in less than 24 h [1–3]. This syndrome, whose etiology remains unclear, usually affects patients between 50 and 80 years [4]. Only few community-based studies have been conducted to determine TGA incidence, with annual incidence rates between 2.9 and 10.4/100,000 [5–9]. Furthermore, data on sex distribution of TGA are discrepant, with some studies reporting male, and other female prevalence [4]. The aim of this study was to determine the incidence of TGA in Merano, province of Bolzano, Northern Italy.
Methods Study area and population The study was conducted in Merano, a town in Northern Italy covering an area of 26 km2. Altitude is 325 m above sea level; the climate is temperate. The study area is served by one general hospital, with one neurology ward. Bolzano
123
Acta Neurol Belg
and Silandro are the two neighboring towns with general hospitals. From July 23, 2003 through July 23, 2013 the mean population was 36,549 (17,484 men and 19,065 women); 11,160 people were aged 55 years and older (4,883 men and 6,277 women).
performed using R Statistical Software (R.0.1, R Foundation for Statistical Computing, Vienna, Austria, http:// www.R-project.org).
Sources of cases
Between July 23, 2003 and July 23, 2013 the total number of patients who have experienced a first-ever TGA was 35 (18 males, 17 females). All cases of TGA occurring in patients residing in the town of Merano were evaluated at the Hospital of Merano, none in the Hospitals of Silandro or Bolzano. All patients presented a pathognomonic clinical picture for TGA, and fulfilled all diagnostic criteria proposed by Caplan [1] and Hodges and Warlow [2], including the exclusion of other causes of amnesia (posttraumatic, drug-induced, metabolic, degenerative, epileptic) according to clinical evaluation and diagnostic examination performed (as specified in the ‘‘Methods’’ section). The mean age of TGA patients recorded was 67.3 years [standard deviation (SD) 5.8], with no differences between men (66.9 years, SD 5.8) and women (67.8 years, SD 5.9). The overall annual crude incidence rate of first-ever-ina-lifetime TGA was 9.6/100,000 inhabitants (9.5 % CI 6.7–13.3), 10.1/100,000 for men and 8.9/100,000 for women (p \ 0.001). After adjustment by the direct method to the European population, the annual incidence rate was 6.4/100,000 population. Table 1 shows the age- and sexspecific incidences for TGA cases ascertained during the study period. The incidence rates increased progressively with age, reaching a maximum at the age group 60–69 years in both sexes, with men being more frequently affected than women (p = 0.003). Conversely, in the age group 70–84 years, women were more frequently affected than men (p \ 0.001).
Cases were identified from multiple sources (years 2003–2013): hospital discharge diagnoses of all the Departments of the Merano city hospital, including first aid Department; Neurology Units of the Bolzano city hospital; all the Departments of the Silandro town hospital. ICD-9 diagnostic code 347.7 and keyword ‘‘amnesia globale transitoria’’ (transient global amnesia, TGA) were used for database searching and filtering. Diagnostic criteria Medical records of all subjects identified from source screening were reviewed to verify the diagnosis of TGA according to criteria proposed by Caplan [1] and Hodges and Warlow [2]. Patients residing in the town of Merano who fulfilled following diagnostic criteria were included in the study: (a) attacks must be witnessed; (b) acute onset of clear-cut anterograde amnesia during the attack; (c) no alteration in consciousness or loss of personal identity as well as any other cognitive impairment other than amnesia; (d) no accompanying neurological symptoms or signs; (e) complete resolution within 24 h; (f) no recent history of head trauma or epileptic seizures; (g) other causes of amnesia must be excluded. Only the cases of first-ever-in-a-lifetime TGA were considered. All patients systematically underwent following examination to rule out other causes of amnesia: neurological evaluation (including an accurate history on drug assumption and head trauma), CT head scan, EEG, laboratory examinations (electrolytes, aspartate amino transferase, blood glucose, creatinine blood test and blood urea nitrogen, blood cells). Data were recorded in digital archives. Statistical analysis The adjusted rates were calculated by the direct method using 10-year age grouping of the European population as a standard [10]. Age- and sex-specific incidence rates were calculated, and 95 % confidence intervals (CIs) were computed using the Poisson distribution [11]. Unpaired Student’s t test (two-tailed test with a level of 0.05) was used to compare the two rates. All the analyses were
123
Results
Discussion This study aimed to provide reliable results on incidence of TGA by adopting a comprehensive approach using all possible case collection sources available in the study area. Incidence rates were computed in a relatively large and well-defined population, considering only the cases of firstever-in-a-lifetime TGA. In all patients, diagnosis was made by neurologists according to the criteria proposed by Caplan [1] and Hodges and Warlow [2], as in most of the recent epidemiological studies on TGA [5–9]. In our study, the mean age of TGA cases was similar to that of other reports [5–9], whereas the crude annual incidence rate for TGA is very similar to that reported in Turku, Finland (10/100,000) [6] and Belluno, Italy (10.4/
Acta Neurol Belg Table 1 Age- and sex-specific annual incident rates of TGA (per 100,000) in Merano, province of Bolzano, Italy Age class (years)
n
Population
Crude incidence rate
Age-standardized incidence rate
Men 0–54
0
12,601
–
–
55–59
1
1,038
9.63
0.58
60–64
6
1,114
53.86
2.69
65–69
6
1,019
58.88
2.36
70–74
3
779
38.51
1.16
75–79
1
567
17.64
0.35
80–84
1
366
27.32
0.27
Total
18
17,484
10.09
7.41
0–54
0
12,788
–
–
55–59
0
1,207
–
–
60–64
7
1,277
54.84
2.74
65–69
4
1,201
33.31
1.33
70–74
2
1,005
19.90
0.60
75–79
4
848
47.17
0.94
80–84
0
739
–
–
Total
17
19,065
8.92
5.61
Women
Age class (years)
Both sexes n
Population
Crude incidence rate
95 % CI
Age-standardized incidence rate
0–54
0
25,389
–
–
–
55–59
1
2,245
4.45
0.06–24.78
0.27
60–64
13
2,391
54.37
28.92–92.98
2.72
65–69
10
2,220
45.05
21.57–82.84
1.80
70–74
5
1,784
28.03
9.03–65.40
0.84
75–79
5
1,415
35.34
11.39–82.64
0.71
80–84
1
1,105
9.05
0.12–50.35
0.09
Total
35
36,549
9.58
6.67–13.32
6.43
predominance in TGA incidence rates found in younger age groups and in all age groups considered as a whole might not be simply explained by the demographic structure of the population. This study has some limitations. The retrospective design of this study may have led to incomplete case collection, with underestimation of true disease incidence. However, the dramatic TGA presentation with abrupt onset of amnesia may have induced most patients to seek for medical advice in hospital; furthermore, in most cases the clinical features of TGA are so straightforward that the diagnosis can be clinically immediately suspected even by inexperienced neurologists without requiring further examinations. For these reasons, it is very unlikely that many cases of TGA have not been recognized and appropriately diagnosed. Patients were diagnosed by different neurologists, and differential diagnoses were excluded according to clinical probability and the judgment of the neurologist. Finally, patients were identified according to the ICD-9 code at hospital discharge, so that misdiagnosed or miscoded patients could not be identified, with possible underestimation of disease incidence. In conclusion, our results show that the incidence rate of TGA in Merano, Italy, does not differ from that reported in Turku, Finland and Belluno, Italy, and confirm that this benign syndrome is relatively common. Our study confirms that TGA occurs mainly in elderly patients. Important discrepancies on sex distribution of TGA among different studies exist, with some groups reporting male, and others female predominance. Further, prospective incidence studies should be conducted to further clarify this aspect. Conflict of interest
There was no conflict of interest.
July 2003–July 2013
References 100,000) [7], and much higher than that estimated in Alcoi, Spain (2.9/100,000) [7] and in Rochester, Minnesota (5.2/ 100,000) [5]. In our study, the incidence of TGA increased with age in both sexes, and was higher in females than in males in older age groups ([70 years), whereas in younger age groups men were more frequently affected. However, considering all age groups, incidence of TGA was significantly higher in males. Although described in some clinical series [2, 12], this male predominance in TGA incidence contrasts with some previous studies reporting higher incidence rates in women [4, 6, 8, 13]. The female predominance noted in older age groups in our study may derive, at least in part, from a relative overrepresentation of women among the elderly. Conversely, the significant male
1. Caplan LR (1985) Transient global amnesia. In: Vinken PJ, Bruyn GW, Klawans HL (eds) Handbook of clinical neurology. Elsevier Science, Amsterdam 2. Hodges JR, Warlow CP (1990) Syndromes of transient amnesia: towards a classification. A study of 153 cases. J Neurol Neurosurg Psychiatry 53:834–843 3. Bartsch T, Deuschl G (2010) Transient global amnesia: functional anatomy and clinical implications. Lancet Neurol 9:205–214 4. Quinette P, Guillery-Girard B, Dayan J, de la Sayette V, Marquis S, Viader F, Desgranges B, Eustache F (2006) What does transient global amnesia really mean? Review of the literature and thorough study of 142 cases. Brain 129:1640–1658 5. Miller JW, Petersen RC, Metter EJ et al (1987) Transient global amnesia: clinical characteristics and prognosis. Neurology 37:733–737 6. Koski KJ, Marttila RJ (1990) Transient global amnesia: incidence in an urban population. Acta Neurol Scand 81:358–360
123
Acta Neurol Belg 7. Matias-Guiu J, Blanquer J, Falip R, Oltra A, Martin M (1992) Incidence of transient global amnesia in a Alcoi (Spain). Acta Neurol Scand 86:221 8. Lauria G, Gentile M, Fassetta G, Casetta I, Caneve G (1997) Incidence of transient global amnesia in the Belluno province, Italy: 1985 through 1995. Results of a community-based study. Acta Neurol Scand 95:303–310 9. Berli R, Hutter A, Waespe W, Bachli EB (2009) Transient global amnesia: not so rare after all. Swiss Med Wkly 139:288–292 10. Ahmad OB, Boschi-Pinto C, Lopez AD, et al (2001) Age standardization of rates: a new WHO standard. GPE Discussion Paper
123
Series: No. 31. EIP/GPE/EBD, World Health Organization 2001 (online). http://www.who.int/healthinfo/paper31.pdf. Accessed 24th July 2013 11. Schoenberg BS (1983) Calculating confidence intervals for rates and ratios. Neuroepidemiology 2:257–265 12. Shuping JR, Rollinson RD, Toole JF (1980) Transient global amnesia. Ann Neurol 7:281–285 13. Melo TP, Ferro JM, Ferro H (1992) Transient global amnesia. A case control study. Brain 115(Pt 1):261–270
ORIGINAL ARTICLE
Incidence of transient global amnesia in Merano, province of Bolzano, Italy Francesco Brigo • Piergiorgio Lochner Frediano Tezzon • Raffaele Nardone
•
Received: 8 January 2014 / Accepted: 22 January 2014 Ó Belgian Neurological Society 2014
Abstract Few community-based studies determined the incidence of transient global amnesia (TGA), with annual incidence rates between 2.9 and 10.4/100,000. Data on sex distribution of TGA are discrepant. Aim of this study was to determine the incidence of TGA in Merano, province of Bolzano, Northern Italy. Cases were identified from hospital discharge diagnoses of all the Departments of the general hospital of Merano and neighboring towns. Patients fulfilling internationally accepted diagnostic criteria for TGA and residing in Merano were included. Crude, age- and sex-specific incidence rates were computed. The overall annual crude incidence rate of TGA was 9.6/100,000 inhabitants (9.5 % confidence interval 6.7–13.3), 10.1/100,000 for men and 8.9/100,000 for women (p \ 0.001). After adjustment by the direct method to the European population, the annual incidence rate was 6.4/100,000. The incidence rate of TGA in Merano, Italy, does not differ from that reported in Turku, Finland and Belluno, Italy. This study confirms that this benign syndrome is relatively common and occurs mainly in elderly patients. However, the higher male predominance in TGA incidence rates contrasts with previous epidemiological studies. Further, prospective incidence F. Brigo (&) Section of Clinical Neurology, Department of Neurological and Movement Sciences, University of Verona, Piazzale L.A. Scuro, 10, 37134 Verona, Italy e-mail: [email protected] F. Brigo P. Lochner F. Tezzon R. Nardone Department of Neurology, Franz Tappeiner Hospital, Merano, Italy R. Nardone Department of Neurology, Christian Doppler Klinik, Paracelsus Medical University, Salzburg, Austria
studies should therefore be conducted to further clarify sex predominance in TGA. Keywords Epidemiology Incidence Italy Transient global amnesia
Introduction Transient global amnesia (TGA) is a benign neurological syndrome characterized by the sudden onset of anterograde amnesia usually associated with repetitive questioning [1– 3]. During the event, consciousness, vigilance, immediate memory, personal identity, and all other cognitive functions are typically intact. Symptoms resolve within a few hours, by definition in less than 24 h [1–3]. This syndrome, whose etiology remains unclear, usually affects patients between 50 and 80 years [4]. Only few community-based studies have been conducted to determine TGA incidence, with annual incidence rates between 2.9 and 10.4/100,000 [5–9]. Furthermore, data on sex distribution of TGA are discrepant, with some studies reporting male, and other female prevalence [4]. The aim of this study was to determine the incidence of TGA in Merano, province of Bolzano, Northern Italy.
Methods Study area and population The study was conducted in Merano, a town in Northern Italy covering an area of 26 km2. Altitude is 325 m above sea level; the climate is temperate. The study area is served by one general hospital, with one neurology ward. Bolzano
123
Acta Neurol Belg
and Silandro are the two neighboring towns with general hospitals. From July 23, 2003 through July 23, 2013 the mean population was 36,549 (17,484 men and 19,065 women); 11,160 people were aged 55 years and older (4,883 men and 6,277 women).
performed using R Statistical Software (R.0.1, R Foundation for Statistical Computing, Vienna, Austria, http:// www.R-project.org).
Sources of cases
Between July 23, 2003 and July 23, 2013 the total number of patients who have experienced a first-ever TGA was 35 (18 males, 17 females). All cases of TGA occurring in patients residing in the town of Merano were evaluated at the Hospital of Merano, none in the Hospitals of Silandro or Bolzano. All patients presented a pathognomonic clinical picture for TGA, and fulfilled all diagnostic criteria proposed by Caplan [1] and Hodges and Warlow [2], including the exclusion of other causes of amnesia (posttraumatic, drug-induced, metabolic, degenerative, epileptic) according to clinical evaluation and diagnostic examination performed (as specified in the ‘‘Methods’’ section). The mean age of TGA patients recorded was 67.3 years [standard deviation (SD) 5.8], with no differences between men (66.9 years, SD 5.8) and women (67.8 years, SD 5.9). The overall annual crude incidence rate of first-ever-ina-lifetime TGA was 9.6/100,000 inhabitants (9.5 % CI 6.7–13.3), 10.1/100,000 for men and 8.9/100,000 for women (p \ 0.001). After adjustment by the direct method to the European population, the annual incidence rate was 6.4/100,000 population. Table 1 shows the age- and sexspecific incidences for TGA cases ascertained during the study period. The incidence rates increased progressively with age, reaching a maximum at the age group 60–69 years in both sexes, with men being more frequently affected than women (p = 0.003). Conversely, in the age group 70–84 years, women were more frequently affected than men (p \ 0.001).
Cases were identified from multiple sources (years 2003–2013): hospital discharge diagnoses of all the Departments of the Merano city hospital, including first aid Department; Neurology Units of the Bolzano city hospital; all the Departments of the Silandro town hospital. ICD-9 diagnostic code 347.7 and keyword ‘‘amnesia globale transitoria’’ (transient global amnesia, TGA) were used for database searching and filtering. Diagnostic criteria Medical records of all subjects identified from source screening were reviewed to verify the diagnosis of TGA according to criteria proposed by Caplan [1] and Hodges and Warlow [2]. Patients residing in the town of Merano who fulfilled following diagnostic criteria were included in the study: (a) attacks must be witnessed; (b) acute onset of clear-cut anterograde amnesia during the attack; (c) no alteration in consciousness or loss of personal identity as well as any other cognitive impairment other than amnesia; (d) no accompanying neurological symptoms or signs; (e) complete resolution within 24 h; (f) no recent history of head trauma or epileptic seizures; (g) other causes of amnesia must be excluded. Only the cases of first-ever-in-a-lifetime TGA were considered. All patients systematically underwent following examination to rule out other causes of amnesia: neurological evaluation (including an accurate history on drug assumption and head trauma), CT head scan, EEG, laboratory examinations (electrolytes, aspartate amino transferase, blood glucose, creatinine blood test and blood urea nitrogen, blood cells). Data were recorded in digital archives. Statistical analysis The adjusted rates were calculated by the direct method using 10-year age grouping of the European population as a standard [10]. Age- and sex-specific incidence rates were calculated, and 95 % confidence intervals (CIs) were computed using the Poisson distribution [11]. Unpaired Student’s t test (two-tailed test with a level of 0.05) was used to compare the two rates. All the analyses were
123
Results
Discussion This study aimed to provide reliable results on incidence of TGA by adopting a comprehensive approach using all possible case collection sources available in the study area. Incidence rates were computed in a relatively large and well-defined population, considering only the cases of firstever-in-a-lifetime TGA. In all patients, diagnosis was made by neurologists according to the criteria proposed by Caplan [1] and Hodges and Warlow [2], as in most of the recent epidemiological studies on TGA [5–9]. In our study, the mean age of TGA cases was similar to that of other reports [5–9], whereas the crude annual incidence rate for TGA is very similar to that reported in Turku, Finland (10/100,000) [6] and Belluno, Italy (10.4/
Acta Neurol Belg Table 1 Age- and sex-specific annual incident rates of TGA (per 100,000) in Merano, province of Bolzano, Italy Age class (years)
n
Population
Crude incidence rate
Age-standardized incidence rate
Men 0–54
0
12,601
–
–
55–59
1
1,038
9.63
0.58
60–64
6
1,114
53.86
2.69
65–69
6
1,019
58.88
2.36
70–74
3
779
38.51
1.16
75–79
1
567
17.64
0.35
80–84
1
366
27.32
0.27
Total
18
17,484
10.09
7.41
0–54
0
12,788
–
–
55–59
0
1,207
–
–
60–64
7
1,277
54.84
2.74
65–69
4
1,201
33.31
1.33
70–74
2
1,005
19.90
0.60
75–79
4
848
47.17
0.94
80–84
0
739
–
–
Total
17
19,065
8.92
5.61
Women
Age class (years)
Both sexes n
Population
Crude incidence rate
95 % CI
Age-standardized incidence rate
0–54
0
25,389
–
–
–
55–59
1
2,245
4.45
0.06–24.78
0.27
60–64
13
2,391
54.37
28.92–92.98
2.72
65–69
10
2,220
45.05
21.57–82.84
1.80
70–74
5
1,784
28.03
9.03–65.40
0.84
75–79
5
1,415
35.34
11.39–82.64
0.71
80–84
1
1,105
9.05
0.12–50.35
0.09
Total
35
36,549
9.58
6.67–13.32
6.43
predominance in TGA incidence rates found in younger age groups and in all age groups considered as a whole might not be simply explained by the demographic structure of the population. This study has some limitations. The retrospective design of this study may have led to incomplete case collection, with underestimation of true disease incidence. However, the dramatic TGA presentation with abrupt onset of amnesia may have induced most patients to seek for medical advice in hospital; furthermore, in most cases the clinical features of TGA are so straightforward that the diagnosis can be clinically immediately suspected even by inexperienced neurologists without requiring further examinations. For these reasons, it is very unlikely that many cases of TGA have not been recognized and appropriately diagnosed. Patients were diagnosed by different neurologists, and differential diagnoses were excluded according to clinical probability and the judgment of the neurologist. Finally, patients were identified according to the ICD-9 code at hospital discharge, so that misdiagnosed or miscoded patients could not be identified, with possible underestimation of disease incidence. In conclusion, our results show that the incidence rate of TGA in Merano, Italy, does not differ from that reported in Turku, Finland and Belluno, Italy, and confirm that this benign syndrome is relatively common. Our study confirms that TGA occurs mainly in elderly patients. Important discrepancies on sex distribution of TGA among different studies exist, with some groups reporting male, and others female predominance. Further, prospective incidence studies should be conducted to further clarify this aspect. Conflict of interest
There was no conflict of interest.
July 2003–July 2013
References 100,000) [7], and much higher than that estimated in Alcoi, Spain (2.9/100,000) [7] and in Rochester, Minnesota (5.2/ 100,000) [5]. In our study, the incidence of TGA increased with age in both sexes, and was higher in females than in males in older age groups ([70 years), whereas in younger age groups men were more frequently affected. However, considering all age groups, incidence of TGA was significantly higher in males. Although described in some clinical series [2, 12], this male predominance in TGA incidence contrasts with some previous studies reporting higher incidence rates in women [4, 6, 8, 13]. The female predominance noted in older age groups in our study may derive, at least in part, from a relative overrepresentation of women among the elderly. Conversely, the significant male
1. Caplan LR (1985) Transient global amnesia. In: Vinken PJ, Bruyn GW, Klawans HL (eds) Handbook of clinical neurology. Elsevier Science, Amsterdam 2. Hodges JR, Warlow CP (1990) Syndromes of transient amnesia: towards a classification. A study of 153 cases. J Neurol Neurosurg Psychiatry 53:834–843 3. Bartsch T, Deuschl G (2010) Transient global amnesia: functional anatomy and clinical implications. Lancet Neurol 9:205–214 4. Quinette P, Guillery-Girard B, Dayan J, de la Sayette V, Marquis S, Viader F, Desgranges B, Eustache F (2006) What does transient global amnesia really mean? Review of the literature and thorough study of 142 cases. Brain 129:1640–1658 5. Miller JW, Petersen RC, Metter EJ et al (1987) Transient global amnesia: clinical characteristics and prognosis. Neurology 37:733–737 6. Koski KJ, Marttila RJ (1990) Transient global amnesia: incidence in an urban population. Acta Neurol Scand 81:358–360
123
Acta Neurol Belg 7. Matias-Guiu J, Blanquer J, Falip R, Oltra A, Martin M (1992) Incidence of transient global amnesia in a Alcoi (Spain). Acta Neurol Scand 86:221 8. Lauria G, Gentile M, Fassetta G, Casetta I, Caneve G (1997) Incidence of transient global amnesia in the Belluno province, Italy: 1985 through 1995. Results of a community-based study. Acta Neurol Scand 95:303–310 9. Berli R, Hutter A, Waespe W, Bachli EB (2009) Transient global amnesia: not so rare after all. Swiss Med Wkly 139:288–292 10. Ahmad OB, Boschi-Pinto C, Lopez AD, et al (2001) Age standardization of rates: a new WHO standard. GPE Discussion Paper
123
Series: No. 31. EIP/GPE/EBD, World Health Organization 2001 (online). http://www.who.int/healthinfo/paper31.pdf. Accessed 24th July 2013 11. Schoenberg BS (1983) Calculating confidence intervals for rates and ratios. Neuroepidemiology 2:257–265 12. Shuping JR, Rollinson RD, Toole JF (1980) Transient global amnesia. Ann Neurol 7:281–285 13. Melo TP, Ferro JM, Ferro H (1992) Transient global amnesia. A case control study. Brain 115(Pt 1):261–270
