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Retrospective study of sensitivity and specificity of EEG in the elderly compared with younger age groups
Epilepsy & Behavior 25 (2012) 408–411
Contents lists available at SciVerse ScienceDirect
Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh
Retrospective study of sensitivity and specificity of EEG in the elderly compared with younger age groups Philip Watson a, Alison Conroy a, Gregory Moran a, Susan Duncan b,⁎ a b
Department of Neurophysiology, Western General Hospital, Edinburgh EH4 2XU, Scotland, UK Edinburgh and South East Scotland Epilepsy Service, Department of Clinical Neurosciences, Western General Hospital, Edinburgh EH4 2XU, Scotland, UK
a r t i c l e
i n f o
Article history: Received 6 June 2012 Revised 18 July 2012 Accepted 31 July 2012 Available online 27 October 2012 Keywords: Epilepsy Elderly EEG Sensitivity Specificity
a b s t r a c t Following a recommendation from a Good Practice Guide published in Scotland stating that EEG should not be routinely used in the diagnosis of epilepsy in the elderly, we conducted a retrospective study to ascertain the effects this recommendation had. We found that predating the recommendation, there had already been a decline in the use of EEG in people aged 65 and over. Detailed examination of a 3.5‐year epoch which straddled 2 years before the recommendation and 1.5 years after its publication revealed no evidence of a change in the type of referrals but just in the number of referrals. Comparison with 2 younger cohorts showed that EEG in the elderly had the same specificity and sensitivity as in the younger age groups and was of particular use in picking up previously unsuspected non-convulsive status. We conclude the EEG remains an important diagnostic adjunct in the elderly. © 2012 Elsevier Inc. All rights reserved.
1. Introduction The uses and limitations of EEG are well documented [1,2], including some authorities' reservations about the utility of EEG in elderly populations [1,3]. In 2008, Epilepsy Scotland, a leading charity, brought together a body of Scottish opinion leaders made up of physicians specializing in medicine for the elderly, neurologists and patient representatives to write a guide to epilepsy in later life. This guide stated that EEG should not be routinely used in the elderly [4]; a sentiment repeated by one of the keynote speakers at the launch of the document in 2008. Interestingly, for a low cost, easily administered test, the use of EEG in the elderly is not mentioned in the SIGN (Scottish Intercollegiate Guidelines Network) [5] or in the NICE (National Institute For Clinical Excellence) guidelines for epilepsy [6], although both SIGN [7] and NICE [8] guidelines for dementia are much more specific if no less encouraging about the role of routine EEG. Against this backdrop, we conducted a retrospective study of EEGs done in our department examining their utility in an elderly population. 2. Aims The aims of the study; were to ascertain the sensitivity and specificity of EEG in the elderly compared with two younger cohorts; ⁎ Corresponding author at: Edinburgh and South East Scotland Epilepsy Service, Department of Clinical Neurosciences, Western General Hospital, Edinburgh, Scotland, UK. E-mail address: [email protected] (S. Duncan). 1525-5050/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org10.1016/j.yebeh.2012.07.030
to scrutinize referral patterns over several years to see if the Epilepsy Scotland's Good Practice Guide and the SIGN guidelines on dementia (2006) had any impact on the referrals; and to examine whether the use of EEG in the elderly made a difference to the clinical outcome. 3. Methods Permission for the study was granted by the Research Ethics Committee. All patients gave consent or were consented under the Adults with Incapacity Act (Scotland). The Department of Neurophysiology at the Western General Hospital in Edinburgh is the sole provider of EEG services to adults over the age of 16 who are residents in Lothian, a region with a total population of 823,122. All EEGs done in the Department of Neurophysiology between August 2004 and August 2011 were identified to ascertain referral trends. Then, an epoch from July 2006 to December 2009 was identified for closer study as this straddled the period before and after the publication of the Good Practice Guide, giving us an opportunity to examine the effects on referrals before and after its publication. The other reason for choosing to begin in 2006 was to maximize the number of people with complete details on the electronic patient record system. Paper referrals for each patient were examined, and data about the patient's age, medical history, and reason for referral were extracted. The reasons for referral were categorized into 1) period of altered or loss of consciousness; 2) focal motor or sensory symptoms; 3) period of confusion or cognitive impairment; 4) clear history from patient or
P. Watson et al. / Epilepsy & Behavior 25 (2012) 408–411
witness of aura or automatism suggestive of seizure; 5) decline in cognitive performance or episode of amnesia; and 6) personality change. Using each individual's unique patient number, the EEG result was correlated with their electronic case record, which everyone who has attended an NHS hospital in the Lothian region area thereby has. The electronic record carries the patient's outpatient and inpatient records, laboratory results and grants access to MR/CT/X-ray images. This enabled clinical correlation between the final diagnosis stated in discharge or death summary and that stated on the EEG request card and the final EEG report. All EEGs were performed on XLTEK equipment and software (version 5.4.0; copyright 1998–2006) using the international 10–20 system. Electroencephalography results were reviewed by nationally accredited clinical physiologists and two physicians (GM and SD). Only the first EEG result was included. Statistical analysis was performed using Minitab v.14. Descriptive, non-parametric, and parametric statistics were performed as appropriate.
4. Results Between August 2004 and August 2011, a total of 5108 EEGs were performed. There was a drop of 60% in the number of referrals of those aged 65 and over. This decline predated the publication of the SIGN guidelines on dementia and the Good Practice Guide. To confirm the decline in the referrals in the 65 plus age group, we examined the numbers of EEGs as a percentage of the total population in 5 age ranges as defined by the Scottish Office for National Statistics [9]; the groups being 16–24 years, 25–44 years, 45–64 years, 65–84 years and 85 years and over. In the year August 2004–2005, 0.13% of the Lothian population over 85 years had an EEG, and between August 2008 and August 2009, it was 0.05%. A similar trend was seen for the 65–84 age group where between 2004 and 2011, there appeared to be an almost 40% decline in the requests for EEG (see Fig. 1). Seven hundred and fifty-four EEGs were done in the period July 2006 to December 2009. To simplify the analysis and improve the statistical power of the sensitivity and specificity calculations, we combined the 5 age bands into 3; 16–44, 45–64, 65 and over. Sixty-six percent of the referrals came from neurologists, 18.3% from assorted medical specialties, including infectious diseases and general medicine, 5.5% from medicine for the elderly, 6.4% from psychiatry and learning disability services and 3.8% from intensive care units. Inspection of the referral patterns for the elderly cohort showed that 15% of the referrals in this group came from the medicine for the elderly physicians. The three commonest reasons for referral for EEG in the elderly group (65 and over) were altered consciousness, i.e. reduction in GCS at the time of EEG or from which the patient had recovered (41%),
0.002 0.0018 0.0016 0.0014 0.0012 0.001 0.0008 0.0006 0.0004 0.0002 0
16-24 25-44 45-64 65-84 85+
Aug Aug Aug Aug Aug Aug Aug 04-05 05-06 06-07 07-08 08-09 09-10 10-11 Fig. 1. Numbers of EEG as a percentage of the background population in that age group.
409
focal motor or sensory symptoms (30%) and confusion or cognitive impairment (29%). In the 40 to 64 age group, the three commonest reasons were focal motor/sensory symptoms (28%), auras or automatisms (22%) and confusion/cognitive impairment (16%). In the youngest group, the three commonest reasons for referral were altered consciousness (20.5%), focal motor or sensory symptoms (19%) and automatisms and auras (12%). Forty-four percent of the 16–39 age group, 36% of the 40–64 age group and 20% of the 65 and over age group had a final diagnosis of epilepsy. The EEG characteristics of each group can be seen in Table 1. As expected, the 65 plus age group was less likely to have a normal EEG compared with the other two groups. The 65 and over group had a significantly higher incidence of status epilepticus than the other groups (N= 11, 5 of whom were referred for non‐specific cognitive decline or confusion). Sensitivity and specificity were calculated for those patients for whom a clear‐cut clinical diagnosis and outcome were recorded in the notes (N = 630). This shows no significant differences in the sensitivity and specificity between the three age groups. Not all outcomes were available because “historic” episodes of care, i.e. consultations that occurred before 2006, were not always available on the electronic records, and some paper records were untraceable. 5. Discussion This is the first study to our knowledge in which the sensitivity and specificity of EEG in the elderly have been compared with those of younger age groups. Because there is only one neurophysiology department serving the Lothian area, we are confident that this study is an accurate reflection of practice in our part of Scotland. Our results show a decline in the use of EEG in the elderly compared with the younger sections of the population which antedated the release of the Epilepsy Scotland's Good Practice Guide and the publication of SIGN guidelines on dementia. The reasons for this decline are unclear, as random inspection of referral forms out with our study period of July 2006 to November 2009 showed no change in the clinical scenarios described on request forms. This finding is not unduly surprising. In an earlier study of the impact of the SIGN guidelines for epilepsy in a Scottish region, the effects of the publication and follow‐up visits from specialist nurses were close to negligible [10]. One previous study compared EEG results in patients who developed epilepsy after the age of 60 with a cohort who developed the condition between the ages of 20 and 40 years. The authors reported that interictal epileptiform discharges (IEDS) were as common in the older age group as in the younger group, although generalized epileptiform discharges were significantly less common [11]. In our study, we did not find IEDS in the elderly population as frequently as in the younger cohorts, especially in the 16–39 age group. This probably reflects the prevalence of epilepsy in each group. Twice as many people in the 16–39 age group had epilepsy as a final diagnosis as the over 65 age group, suggesting that had we selected a group of older patients with epilepsy, the EEG might have been performed as well as in the study mentioned above. Interestingly, the incidence of IEDs was lower than in the two previous studies for all age groups [11,3]. This probably reflects the fact that, as far as we could ascertain, these EEGs were all performed when the subjects were awake and none of the subjects were sleep deprived. Interictal epileptiform discharges are known to increase during stage one and stage two of sleep. This is particularly true for the younger patients [12]. Our results suggest EEG performed as well in the elderly age group as in the younger patients, but the diagnostic questions it was asked to answer were often different to younger age groups. The elderly were much more likely to be referred because of prolonged altered consciousness, confusion or behavioral changes, unlike the younger cohorts who were more likely to be referred for paroxysmal events. One of the reasons EEG was performed as well in the elderly group
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P. Watson et al. / Epilepsy & Behavior 25 (2012) 408–411
Table 1 Characteristics of study population. Age group
N
Mean age
Diagnostic EEG (epilepsy)
Diagnostic EEG (encephalopathy)
Non‐diagnostic EEG
16–39 40–64 65 and over Chi square
216 216 198
26.6 (16–39) 50 (40–54) 74 (65–93)
45 (19.7%)* 23 (10%) 24 (10.9%) *P = 0.009 compared with the 40–64 and 65 plus age groups
4 (1.7%) 10 (4.3%)* 14 (6.4%)** *P = 0.003 compared with the 16–39 age group **P = 0.04 compared with the 16–39 age group
179 (78.5%) 197 (85.7%) 182 (82.7%)
16–39 40–64 65 and over Chi square
253 253 248
16–39 40–64 65 and over
216 216 198
Normal EEG
Focal slowing
Generalized slowing
Focal sharp wavesa
Spike and wave
Status
149 (60%) 152 (60%) 106 (43%)* *P = 0.001 compared with the 16–39 and 40–64 age groups
25 (10%) 25 (10%) 21 (8.5%)
15 (6%) 27 (11%)* 65 (26.5%)** *P = 0.03 compared with the 16–39 age group **P=0.001 compared with the 16–39 and 40–64 age groups
17 (7%) 25 (10%) 40 (16%)* *P=0.006 compared with the 16–39 age group
40 (16%)* 19 (8%) 2 (0.8%) *P = 0.001 compared with both the 40–64 and 65 plus age groups
3 (1.2%) 1 (0.4%) 11 (4.5%)* *P = 0.005 compared with both the 40–64 and 65 plus age groups
True positives
True negatives
False positives
False negatives
Sensitivity
Specificity
42 37 28
106 122 127
5 1 1
63 56 42
0.4 0.39 0.4
0.95 0.99 0.99
a Defined as SREDA, non-specific sharp transients, and wicket spikes. Periodic Lateralised Epileptiform Discharges and triphasic waves were also included although these are considered pathological.
was the number of cases of status epilepticus, either convulsive or non-convulsive (NCS), that confirmed in the former or revealed in the latter case. We identified 11 cases of status in the over 65 group in the period July 2006–December 2009, 5 of whom were unsuspected NCS having been sent also with memory problems and confusion. This is in keeping with reports of the incidence of NCS [13], although convulsive status appeared less common in our population [14]. One reason may be that we do not run an out‐of‐hours service and any obvious convulsive status is treated immediately, so by the time an EEG is done, the status has resolved. Of particular note was the observation that only one case of status was referred by medicine for the elderly. The patient had NCS and reported non‐specific sensory symptoms, and had been noted to have involuntary twitching, and had no previous history of epilepsy. Another explanation the EEG findings in this study was our decision to include as true positives EEGs with generalized slowing with or without triphasic waves if the final diagnosis was of an encephalopathy, whether metabolic, degenerative or infective as long as one of those diagnoses was mentioned on the request card. Some may feel this is rather too broad a definition of sensitivity and specificity. Similarly, we counted PLEDS as true positives if the patient had one of the recognized underlying causes of this EEG abnormality, namely acute stroke, subdural hematoma, encephalitis, seizures, Creutzfeldt-Jakob disease, or chronic structural lesion [15]. Our decision to include the first EEG only can be criticized as repeat sampling has been shown to improve capture of epileptiform abnormalities, just as recent work suggests that prolonged monitoring in the elderly may increase the yield of diagnostic EEGs [16]. This was a pragmatic decision taken because many of the elderly only had one EEG before succumbing. One reason authors have not recommended routine EEG in the elderly has been the occurrence of epileptiform activity in people without epilepsy [1]. The one study in this area that is quoted [17] was done in a telemetry unit with more prolonged recording and reported 26% had interictal epileptiform abnormalities. In our study, it was less than 14%. We excluded triphasic waves, although some authorities consider these wave forms to be indicative of a postictal state in some cases, because none of the cases with triphasic waves had seizures recorded in their case notes. We included PLEDS as these
are considered IEDS. Our results are broadly in keeping with a similar study in the elderly [18]. The EEG results in the elderly group were more likely to exhibit generalized slowing and focal sharp waves compared with the other two groups; both of these findings have been reported in previous studies of EEG in the healthy elderly [19]. Focal slowing has classically been taught as suggestive of a space‐occupying lesion. Only one was identified in the entire cohort of 630 patients for whom outcomes were known, and this had been previously identified. One aspect of the referral patterns that is interesting is how few people were referred for purely cognitive problems. The 30% of the referrals that fell under the rubric of confusion usually had behavioral signs or experiential symptoms. It is in this area that the EEG may be of most use in the elderly. Recent work suggests the quantative EEG may show characteristic patterns which might help differentiate between Alzheimers disease, diffuse Lewy body dementia and Parkinson's disease dementia [20], and there have been reportes of specific abnormalites during hypoventilation in asymptomatic carriers of the pre-senelin gene [21]. In summary, this study demonstrates that for the evaluation of confusion and altered consciousness in the elderly, the EEG has a role and should not be abandoned. Its utility in the evaluation of paroxysmal events is limited because few EEG results in the elderly exhibit spike and wave or photosensitivity which in younger populations may help with the final diagnosis. This study also reminds us that NCS in the elderly continues to catch us unawares.
References [1] Brodie MJ, Elder AT, Kwan P. Epilepsy in later life. Lancet 2009;8:1019-30. [2] Smith SJM. EEG in the diagnosis, classification and management of patients with epilepsy. J Neurol Neurosurg Psychiatry 2005;Suppl. 2:2-7. [3] Drury I, Beydoun A. Interictal epileptiform activity in elderly patients with epilepsy. Electroencephologr Clin Neurophysiol 1998;106:1019-30. [4] Elder A, Davenport D, Duncan R, et al. Epilepsy in Later Life: a Good Practice Guide. Epilepsy Scotland. www.epilepsyscotland.org.uk; 2008. [5] Scottish Intercollegiate Guidelines Network (SIGN). Diagnosis and management of epilepsy in adults. A national clinical guideline. Guideline 70; 2003. Edinburgh. [6] NICE. The epilepsies: the diagnosis and management of the epilepsies in adults and children in primary and secondary care. London: Institute for Clinical Excellence; 2004.
P. Watson et al. / Epilepsy & Behavior 25 (2012) 408–411 [7] SIGN. Guideline 86. Management of patients with dementia. 26 Thistle Street, Edinburgh EH2 1 EN: Scottish Intercollegiate Guidelines Network; 2006. [8] NICE. Clinical guideline 42. Supporting people with dementia and their careers in health and social care. MidCity Place, 71 High Holborn, London WL1V 6NA: National Institute for Health and Clinical Excellence; 2006. [9] General Register Office for Scotland. http://www.gro-scotland.gov.uk/census/ censushm/index.html; 2001. [10] Davis J, Roberts R, Davidson DLW. Implementation strategies for a Scottish national epilepsy guideline in primary care: results of Tayside Implementation of Guidelines in Epilepsia Randomized (TIGER) trial. Epilepsy 2004;45:28-34. [11] Hughes JR, Zialcita ML. EEG and epilepsy in the elderly compared to a younger group. Clin EEG Neurosci 1999;30:126-31. [12] Molaie M, Cruz A. The effect of sleep deprivation on the rate of focal interictal epileptiform discharges. Electroencephalogr Clin Neurophysiol 1998;70(4):288-92. [13] Maganti R, Gerber P, Drees C, Chung S. Nonconvulsive status epilepticus. Epilepsy Behav 2008;12:572-86. [14] Chen JW, Wasterlein C. Status epilepticus: pathophysiology and management in adults. Lancet Neurol 2006;5:246-56.
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[15] Kalamangalam G, Diehl B, Burgess R. Neuroimaging and neurophysiology of periodic lateralized epileptiform discharges: observations and hypothesis. Epilepsia 2007;48(7):1396-405. [16] Naeije G, Gaspard N, Depondt C, Pepersack T, Legros B. Acute confusional state of unknown cause in the elderly: a study with continuous EEG monitoring. Epilepsy Behav 2012;23:330-4. [17] McBride A, Shih T, Hirsch L. Video-EEG monitoring in the elderly: a review of 94 patients. Epilepsia 2002;43:165-9. [18] Nguyen Michel V, Ourabah Z, Bourdali Y, et al. The yield of routine EEG in geriatric patients: a prospective hospital based study. Neurophysiol Clin 2010;40:249-54. [19] Widdes-Walsh P, Sweeny B, Galvin R, McNamara B. Utilization and yield of EEG in the elderly population. J Clin Neurophysiol 2005;22(4):253-5. [20] Bonanni L, Thomas A, Tiraboschi P, Perfetti B, Varanesi E, Onofrj M. EEG comparisons in early Alzheimers Disease, Dementia with Lewy Bodies and Parkinson's Disease with dementia patients. A two year follow up. Brain 2008;131:690-705. [21] Ponomarova N, Korovaitseva G, Rogaev E. EEG alterations in non-demented individuals related to apolipoprotein E genotype and risk of Alzheimers. Neurobiol Aging 2008;29:819-27.
Contents lists available at SciVerse ScienceDirect
Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh
Retrospective study of sensitivity and specificity of EEG in the elderly compared with younger age groups Philip Watson a, Alison Conroy a, Gregory Moran a, Susan Duncan b,⁎ a b
Department of Neurophysiology, Western General Hospital, Edinburgh EH4 2XU, Scotland, UK Edinburgh and South East Scotland Epilepsy Service, Department of Clinical Neurosciences, Western General Hospital, Edinburgh EH4 2XU, Scotland, UK
a r t i c l e
i n f o
Article history: Received 6 June 2012 Revised 18 July 2012 Accepted 31 July 2012 Available online 27 October 2012 Keywords: Epilepsy Elderly EEG Sensitivity Specificity
a b s t r a c t Following a recommendation from a Good Practice Guide published in Scotland stating that EEG should not be routinely used in the diagnosis of epilepsy in the elderly, we conducted a retrospective study to ascertain the effects this recommendation had. We found that predating the recommendation, there had already been a decline in the use of EEG in people aged 65 and over. Detailed examination of a 3.5‐year epoch which straddled 2 years before the recommendation and 1.5 years after its publication revealed no evidence of a change in the type of referrals but just in the number of referrals. Comparison with 2 younger cohorts showed that EEG in the elderly had the same specificity and sensitivity as in the younger age groups and was of particular use in picking up previously unsuspected non-convulsive status. We conclude the EEG remains an important diagnostic adjunct in the elderly. © 2012 Elsevier Inc. All rights reserved.
1. Introduction The uses and limitations of EEG are well documented [1,2], including some authorities' reservations about the utility of EEG in elderly populations [1,3]. In 2008, Epilepsy Scotland, a leading charity, brought together a body of Scottish opinion leaders made up of physicians specializing in medicine for the elderly, neurologists and patient representatives to write a guide to epilepsy in later life. This guide stated that EEG should not be routinely used in the elderly [4]; a sentiment repeated by one of the keynote speakers at the launch of the document in 2008. Interestingly, for a low cost, easily administered test, the use of EEG in the elderly is not mentioned in the SIGN (Scottish Intercollegiate Guidelines Network) [5] or in the NICE (National Institute For Clinical Excellence) guidelines for epilepsy [6], although both SIGN [7] and NICE [8] guidelines for dementia are much more specific if no less encouraging about the role of routine EEG. Against this backdrop, we conducted a retrospective study of EEGs done in our department examining their utility in an elderly population. 2. Aims The aims of the study; were to ascertain the sensitivity and specificity of EEG in the elderly compared with two younger cohorts; ⁎ Corresponding author at: Edinburgh and South East Scotland Epilepsy Service, Department of Clinical Neurosciences, Western General Hospital, Edinburgh, Scotland, UK. E-mail address: [email protected] (S. Duncan). 1525-5050/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org10.1016/j.yebeh.2012.07.030
to scrutinize referral patterns over several years to see if the Epilepsy Scotland's Good Practice Guide and the SIGN guidelines on dementia (2006) had any impact on the referrals; and to examine whether the use of EEG in the elderly made a difference to the clinical outcome. 3. Methods Permission for the study was granted by the Research Ethics Committee. All patients gave consent or were consented under the Adults with Incapacity Act (Scotland). The Department of Neurophysiology at the Western General Hospital in Edinburgh is the sole provider of EEG services to adults over the age of 16 who are residents in Lothian, a region with a total population of 823,122. All EEGs done in the Department of Neurophysiology between August 2004 and August 2011 were identified to ascertain referral trends. Then, an epoch from July 2006 to December 2009 was identified for closer study as this straddled the period before and after the publication of the Good Practice Guide, giving us an opportunity to examine the effects on referrals before and after its publication. The other reason for choosing to begin in 2006 was to maximize the number of people with complete details on the electronic patient record system. Paper referrals for each patient were examined, and data about the patient's age, medical history, and reason for referral were extracted. The reasons for referral were categorized into 1) period of altered or loss of consciousness; 2) focal motor or sensory symptoms; 3) period of confusion or cognitive impairment; 4) clear history from patient or
P. Watson et al. / Epilepsy & Behavior 25 (2012) 408–411
witness of aura or automatism suggestive of seizure; 5) decline in cognitive performance or episode of amnesia; and 6) personality change. Using each individual's unique patient number, the EEG result was correlated with their electronic case record, which everyone who has attended an NHS hospital in the Lothian region area thereby has. The electronic record carries the patient's outpatient and inpatient records, laboratory results and grants access to MR/CT/X-ray images. This enabled clinical correlation between the final diagnosis stated in discharge or death summary and that stated on the EEG request card and the final EEG report. All EEGs were performed on XLTEK equipment and software (version 5.4.0; copyright 1998–2006) using the international 10–20 system. Electroencephalography results were reviewed by nationally accredited clinical physiologists and two physicians (GM and SD). Only the first EEG result was included. Statistical analysis was performed using Minitab v.14. Descriptive, non-parametric, and parametric statistics were performed as appropriate.
4. Results Between August 2004 and August 2011, a total of 5108 EEGs were performed. There was a drop of 60% in the number of referrals of those aged 65 and over. This decline predated the publication of the SIGN guidelines on dementia and the Good Practice Guide. To confirm the decline in the referrals in the 65 plus age group, we examined the numbers of EEGs as a percentage of the total population in 5 age ranges as defined by the Scottish Office for National Statistics [9]; the groups being 16–24 years, 25–44 years, 45–64 years, 65–84 years and 85 years and over. In the year August 2004–2005, 0.13% of the Lothian population over 85 years had an EEG, and between August 2008 and August 2009, it was 0.05%. A similar trend was seen for the 65–84 age group where between 2004 and 2011, there appeared to be an almost 40% decline in the requests for EEG (see Fig. 1). Seven hundred and fifty-four EEGs were done in the period July 2006 to December 2009. To simplify the analysis and improve the statistical power of the sensitivity and specificity calculations, we combined the 5 age bands into 3; 16–44, 45–64, 65 and over. Sixty-six percent of the referrals came from neurologists, 18.3% from assorted medical specialties, including infectious diseases and general medicine, 5.5% from medicine for the elderly, 6.4% from psychiatry and learning disability services and 3.8% from intensive care units. Inspection of the referral patterns for the elderly cohort showed that 15% of the referrals in this group came from the medicine for the elderly physicians. The three commonest reasons for referral for EEG in the elderly group (65 and over) were altered consciousness, i.e. reduction in GCS at the time of EEG or from which the patient had recovered (41%),
0.002 0.0018 0.0016 0.0014 0.0012 0.001 0.0008 0.0006 0.0004 0.0002 0
16-24 25-44 45-64 65-84 85+
Aug Aug Aug Aug Aug Aug Aug 04-05 05-06 06-07 07-08 08-09 09-10 10-11 Fig. 1. Numbers of EEG as a percentage of the background population in that age group.
409
focal motor or sensory symptoms (30%) and confusion or cognitive impairment (29%). In the 40 to 64 age group, the three commonest reasons were focal motor/sensory symptoms (28%), auras or automatisms (22%) and confusion/cognitive impairment (16%). In the youngest group, the three commonest reasons for referral were altered consciousness (20.5%), focal motor or sensory symptoms (19%) and automatisms and auras (12%). Forty-four percent of the 16–39 age group, 36% of the 40–64 age group and 20% of the 65 and over age group had a final diagnosis of epilepsy. The EEG characteristics of each group can be seen in Table 1. As expected, the 65 plus age group was less likely to have a normal EEG compared with the other two groups. The 65 and over group had a significantly higher incidence of status epilepticus than the other groups (N= 11, 5 of whom were referred for non‐specific cognitive decline or confusion). Sensitivity and specificity were calculated for those patients for whom a clear‐cut clinical diagnosis and outcome were recorded in the notes (N = 630). This shows no significant differences in the sensitivity and specificity between the three age groups. Not all outcomes were available because “historic” episodes of care, i.e. consultations that occurred before 2006, were not always available on the electronic records, and some paper records were untraceable. 5. Discussion This is the first study to our knowledge in which the sensitivity and specificity of EEG in the elderly have been compared with those of younger age groups. Because there is only one neurophysiology department serving the Lothian area, we are confident that this study is an accurate reflection of practice in our part of Scotland. Our results show a decline in the use of EEG in the elderly compared with the younger sections of the population which antedated the release of the Epilepsy Scotland's Good Practice Guide and the publication of SIGN guidelines on dementia. The reasons for this decline are unclear, as random inspection of referral forms out with our study period of July 2006 to November 2009 showed no change in the clinical scenarios described on request forms. This finding is not unduly surprising. In an earlier study of the impact of the SIGN guidelines for epilepsy in a Scottish region, the effects of the publication and follow‐up visits from specialist nurses were close to negligible [10]. One previous study compared EEG results in patients who developed epilepsy after the age of 60 with a cohort who developed the condition between the ages of 20 and 40 years. The authors reported that interictal epileptiform discharges (IEDS) were as common in the older age group as in the younger group, although generalized epileptiform discharges were significantly less common [11]. In our study, we did not find IEDS in the elderly population as frequently as in the younger cohorts, especially in the 16–39 age group. This probably reflects the prevalence of epilepsy in each group. Twice as many people in the 16–39 age group had epilepsy as a final diagnosis as the over 65 age group, suggesting that had we selected a group of older patients with epilepsy, the EEG might have been performed as well as in the study mentioned above. Interestingly, the incidence of IEDs was lower than in the two previous studies for all age groups [11,3]. This probably reflects the fact that, as far as we could ascertain, these EEGs were all performed when the subjects were awake and none of the subjects were sleep deprived. Interictal epileptiform discharges are known to increase during stage one and stage two of sleep. This is particularly true for the younger patients [12]. Our results suggest EEG performed as well in the elderly age group as in the younger patients, but the diagnostic questions it was asked to answer were often different to younger age groups. The elderly were much more likely to be referred because of prolonged altered consciousness, confusion or behavioral changes, unlike the younger cohorts who were more likely to be referred for paroxysmal events. One of the reasons EEG was performed as well in the elderly group
410
P. Watson et al. / Epilepsy & Behavior 25 (2012) 408–411
Table 1 Characteristics of study population. Age group
N
Mean age
Diagnostic EEG (epilepsy)
Diagnostic EEG (encephalopathy)
Non‐diagnostic EEG
16–39 40–64 65 and over Chi square
216 216 198
26.6 (16–39) 50 (40–54) 74 (65–93)
45 (19.7%)* 23 (10%) 24 (10.9%) *P = 0.009 compared with the 40–64 and 65 plus age groups
4 (1.7%) 10 (4.3%)* 14 (6.4%)** *P = 0.003 compared with the 16–39 age group **P = 0.04 compared with the 16–39 age group
179 (78.5%) 197 (85.7%) 182 (82.7%)
16–39 40–64 65 and over Chi square
253 253 248
16–39 40–64 65 and over
216 216 198
Normal EEG
Focal slowing
Generalized slowing
Focal sharp wavesa
Spike and wave
Status
149 (60%) 152 (60%) 106 (43%)* *P = 0.001 compared with the 16–39 and 40–64 age groups
25 (10%) 25 (10%) 21 (8.5%)
15 (6%) 27 (11%)* 65 (26.5%)** *P = 0.03 compared with the 16–39 age group **P=0.001 compared with the 16–39 and 40–64 age groups
17 (7%) 25 (10%) 40 (16%)* *P=0.006 compared with the 16–39 age group
40 (16%)* 19 (8%) 2 (0.8%) *P = 0.001 compared with both the 40–64 and 65 plus age groups
3 (1.2%) 1 (0.4%) 11 (4.5%)* *P = 0.005 compared with both the 40–64 and 65 plus age groups
True positives
True negatives
False positives
False negatives
Sensitivity
Specificity
42 37 28
106 122 127
5 1 1
63 56 42
0.4 0.39 0.4
0.95 0.99 0.99
a Defined as SREDA, non-specific sharp transients, and wicket spikes. Periodic Lateralised Epileptiform Discharges and triphasic waves were also included although these are considered pathological.
was the number of cases of status epilepticus, either convulsive or non-convulsive (NCS), that confirmed in the former or revealed in the latter case. We identified 11 cases of status in the over 65 group in the period July 2006–December 2009, 5 of whom were unsuspected NCS having been sent also with memory problems and confusion. This is in keeping with reports of the incidence of NCS [13], although convulsive status appeared less common in our population [14]. One reason may be that we do not run an out‐of‐hours service and any obvious convulsive status is treated immediately, so by the time an EEG is done, the status has resolved. Of particular note was the observation that only one case of status was referred by medicine for the elderly. The patient had NCS and reported non‐specific sensory symptoms, and had been noted to have involuntary twitching, and had no previous history of epilepsy. Another explanation the EEG findings in this study was our decision to include as true positives EEGs with generalized slowing with or without triphasic waves if the final diagnosis was of an encephalopathy, whether metabolic, degenerative or infective as long as one of those diagnoses was mentioned on the request card. Some may feel this is rather too broad a definition of sensitivity and specificity. Similarly, we counted PLEDS as true positives if the patient had one of the recognized underlying causes of this EEG abnormality, namely acute stroke, subdural hematoma, encephalitis, seizures, Creutzfeldt-Jakob disease, or chronic structural lesion [15]. Our decision to include the first EEG only can be criticized as repeat sampling has been shown to improve capture of epileptiform abnormalities, just as recent work suggests that prolonged monitoring in the elderly may increase the yield of diagnostic EEGs [16]. This was a pragmatic decision taken because many of the elderly only had one EEG before succumbing. One reason authors have not recommended routine EEG in the elderly has been the occurrence of epileptiform activity in people without epilepsy [1]. The one study in this area that is quoted [17] was done in a telemetry unit with more prolonged recording and reported 26% had interictal epileptiform abnormalities. In our study, it was less than 14%. We excluded triphasic waves, although some authorities consider these wave forms to be indicative of a postictal state in some cases, because none of the cases with triphasic waves had seizures recorded in their case notes. We included PLEDS as these
are considered IEDS. Our results are broadly in keeping with a similar study in the elderly [18]. The EEG results in the elderly group were more likely to exhibit generalized slowing and focal sharp waves compared with the other two groups; both of these findings have been reported in previous studies of EEG in the healthy elderly [19]. Focal slowing has classically been taught as suggestive of a space‐occupying lesion. Only one was identified in the entire cohort of 630 patients for whom outcomes were known, and this had been previously identified. One aspect of the referral patterns that is interesting is how few people were referred for purely cognitive problems. The 30% of the referrals that fell under the rubric of confusion usually had behavioral signs or experiential symptoms. It is in this area that the EEG may be of most use in the elderly. Recent work suggests the quantative EEG may show characteristic patterns which might help differentiate between Alzheimers disease, diffuse Lewy body dementia and Parkinson's disease dementia [20], and there have been reportes of specific abnormalites during hypoventilation in asymptomatic carriers of the pre-senelin gene [21]. In summary, this study demonstrates that for the evaluation of confusion and altered consciousness in the elderly, the EEG has a role and should not be abandoned. Its utility in the evaluation of paroxysmal events is limited because few EEG results in the elderly exhibit spike and wave or photosensitivity which in younger populations may help with the final diagnosis. This study also reminds us that NCS in the elderly continues to catch us unawares.
References [1] Brodie MJ, Elder AT, Kwan P. Epilepsy in later life. Lancet 2009;8:1019-30. [2] Smith SJM. EEG in the diagnosis, classification and management of patients with epilepsy. J Neurol Neurosurg Psychiatry 2005;Suppl. 2:2-7. [3] Drury I, Beydoun A. Interictal epileptiform activity in elderly patients with epilepsy. Electroencephologr Clin Neurophysiol 1998;106:1019-30. [4] Elder A, Davenport D, Duncan R, et al. Epilepsy in Later Life: a Good Practice Guide. Epilepsy Scotland. www.epilepsyscotland.org.uk; 2008. [5] Scottish Intercollegiate Guidelines Network (SIGN). Diagnosis and management of epilepsy in adults. A national clinical guideline. Guideline 70; 2003. Edinburgh. [6] NICE. The epilepsies: the diagnosis and management of the epilepsies in adults and children in primary and secondary care. London: Institute for Clinical Excellence; 2004.
P. Watson et al. / Epilepsy & Behavior 25 (2012) 408–411 [7] SIGN. Guideline 86. Management of patients with dementia. 26 Thistle Street, Edinburgh EH2 1 EN: Scottish Intercollegiate Guidelines Network; 2006. [8] NICE. Clinical guideline 42. Supporting people with dementia and their careers in health and social care. MidCity Place, 71 High Holborn, London WL1V 6NA: National Institute for Health and Clinical Excellence; 2006. [9] General Register Office for Scotland. http://www.gro-scotland.gov.uk/census/ censushm/index.html; 2001. [10] Davis J, Roberts R, Davidson DLW. Implementation strategies for a Scottish national epilepsy guideline in primary care: results of Tayside Implementation of Guidelines in Epilepsia Randomized (TIGER) trial. Epilepsy 2004;45:28-34. [11] Hughes JR, Zialcita ML. EEG and epilepsy in the elderly compared to a younger group. Clin EEG Neurosci 1999;30:126-31. [12] Molaie M, Cruz A. The effect of sleep deprivation on the rate of focal interictal epileptiform discharges. Electroencephalogr Clin Neurophysiol 1998;70(4):288-92. [13] Maganti R, Gerber P, Drees C, Chung S. Nonconvulsive status epilepticus. Epilepsy Behav 2008;12:572-86. [14] Chen JW, Wasterlein C. Status epilepticus: pathophysiology and management in adults. Lancet Neurol 2006;5:246-56.
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[15] Kalamangalam G, Diehl B, Burgess R. Neuroimaging and neurophysiology of periodic lateralized epileptiform discharges: observations and hypothesis. Epilepsia 2007;48(7):1396-405. [16] Naeije G, Gaspard N, Depondt C, Pepersack T, Legros B. Acute confusional state of unknown cause in the elderly: a study with continuous EEG monitoring. Epilepsy Behav 2012;23:330-4. [17] McBride A, Shih T, Hirsch L. Video-EEG monitoring in the elderly: a review of 94 patients. Epilepsia 2002;43:165-9. [18] Nguyen Michel V, Ourabah Z, Bourdali Y, et al. The yield of routine EEG in geriatric patients: a prospective hospital based study. Neurophysiol Clin 2010;40:249-54. [19] Widdes-Walsh P, Sweeny B, Galvin R, McNamara B. Utilization and yield of EEG in the elderly population. J Clin Neurophysiol 2005;22(4):253-5. [20] Bonanni L, Thomas A, Tiraboschi P, Perfetti B, Varanesi E, Onofrj M. EEG comparisons in early Alzheimers Disease, Dementia with Lewy Bodies and Parkinson's Disease with dementia patients. A two year follow up. Brain 2008;131:690-705. [21] Ponomarova N, Korovaitseva G, Rogaev E. EEG alterations in non-demented individuals related to apolipoprotein E genotype and risk of Alzheimers. Neurobiol Aging 2008;29:819-27.