epilepsja.pdf

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PAPER

Which electroencephalography (EEG) for epilepsy?

The relative usefulness of different EEG protocols in

patients with possible epilepsy

J P Leach, L J Stephen, C Salveta, M J Brodie

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J Neurol Neurosurg Psychiatry 2006;77:1040–1042. doi: 10.1136/jnnp.2005.084871

See end of article for

authors’ affiliations

.......................

Correspondence to:

J P Leach, Epilepsy Unit,

Western Infirmary,

Glasgow G11 6NT, UK;

johnpaul.leach@sgh.scot.

nhs.uk

Background and aim: Electroencephalography (EEG) is an essential investigative tool for use in young

people with epilepsy. This study assesses the effects of different EEG protocols on the yield of EEG

abnormalities in young people with possible new epilepsy.

Methods: 85 patients presenting to the unit underwent three EEGs with differing protocols: routine EEG (r-

EEG), sleep-deprived EEG (SD-EEG), EEG carried out during drug-induced sleep (DI-EEG). The yield of

EEG abnormalities was compared using each EEG protocol.

Results: 98 patients were recruited to the study. Of the 85 patients who completed the study, 33 (39%)

showed no discernible abnormality on any of their EEG recordings. 36 patients (43%) showed generalised

spike and wave during at least one EEG recording, whereas 15 (18%) had a focal discharge evident at

some stage. SD-EEG had a sensitivity of 92% among these patients, whereas the sensitivity of DI-EEG and

r-EEG was 58% and 44%, respectively. The difference between the yield from SD-EEG was significantly

higher than that from other protocols (p , 0.001). Among the 15 patients showing focal discharges, SD-

EEG provoked abnormalities in 11 (73%). r-EEG and DI-EEG each produced abnormalities in 40% and

27%, respectively. 7 patients (47%) had changes seen only after sleep deprivation. In 2 (13%), the only

abnormalities were seen on r-EEG. In only 1 patient with focal discharges (7%) was the focal change noted

solely after drug-induced sleep. These differences did not reach significance.

Conclusion: EEG has an important role in the classification of epilepsies. SD-EEG is an easy and

inexpensive way of increasing the yield of EEG abnormalities. Using this as the preferred protocol may

help reduce the numbers of EEGs carried out in young patients presenting with epilepsy.

Received

25 November 2005

Revised version received

12 June 2006

Accepted 21 June 2006

Published Online First

26 June 2006

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tive tool for use in young people with epilepsy. 1–5 The

clinical onset of the idiopathic generalised epilepsies

(IGEs) is most common in adolescence and early adulthood,

and this is when EEG is most valuable. 5 Differentiation of

IGE from partial epilepsy should be done as early as possible,

because of the important implications it will have on

treatment choice, 6 planned duration of treatment 6 and

prognosis. 7 Despite its utility, EEG is not always easily

available in many parts of the UK. Clinical targeting is

desirable to allow efficient use of this resource. 8

The effect of sleep deprivation on EEG has long been

recognised. 239 For reasons that are unclear, the incidence of

epileptiform abnormalities on EEG is increased by sleep

deprivation. Some authors feel that this effect leads to an

enhanced yield of epileptiform abnormalities even when

compared with routine EEG (r-EEG) that includes a period of

sleep, 3 although one study did not support the special effect

of sleep deprivation. 4

Although the role of the EEG in early epilepsy is widely

recognised in this age group, there are few data on the

relative sensitivity of EEG protocols in detecting epileptiform

changes. One study 9 looked at the incidence and frequency of

epileptiform abnormalities after EEG with drug-induced

sleep (DI-EEG) and EEG after sleep deprivation (SD-EEG).

This cohort consisted largely of patients already on treatment

for localisation-related epilepsies.

Carpay et al 10 repeated SD-EEG in a cohort of younger

people with normal r-EEG and found that 34% of them

showed various epileptiform abnormalities. The age range

and selection criteria limit the applicability of these data. An

earlier study 11

had a previously normal r-EEG, some of whom were

receiving drugs for epilepsy. Despite this, 47 patients

exhibited some clearly ictal activity, but this selection

precluded direct comparison of elicited epileptiform changes

in different protocols.

In young adults with newly diagnosed epilepsies, the role

of provocative testing (either SD-EEG or DI-EEG) remains

unclear, as the relative yield of generalised discharges in each

protocol has yet to be properly compared. In young adults

with newly diagnosed epilepsy, which EEG protocol is best?

Should SD-EEG be the preferred protocol? Is DI-EEG as

sensitive or specific as SD-EEG in detecting abnormalities?

METHODS

Patients ,35 years of age with possible new epilepsy were

recruited to the study after receiving informed written

consent from them to undergo three EEGs before starting

treatment. All patients had experienced at least two general-

ised tonic–clonic seizures. This study was approved by the

West Glasgow medical ethics committee. Each patient was

assigned to undergo EEGs in random order, one of each of

the three protocols: without specific patient preparation (r-

EEG), after sleep deprivation (SD-EEG) or after receiving oral

temazepam (DI-EEG). Initial EEG was carried out approxi-

mately 4 weeks after the presenting event, whereas subse-

quent EEG recordings were separated by at least 7 days. The

particulars of the different protocols are as follows:

had carried out SD-EEG in 114 patients who

Abbreviations: DI-EEG, EEG during drug-induced sleep; EEG,

electroencephalography; IGE, idiopathic generalised epilepsy; r-EEG,

routine EEG; SD-EEG, EEG after sleep deprivation

www.jnnp.com

E lectroencephalography (EEG) is an essential investiga-

EEG protocols in patients with epilepsy

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Table 1 Characteristics of each recording grouped by protocol

DI-EEG (n = 94)

r–EEG (n = 99)

SD-EEG (n = 92)

Median duration (min)

21.8

40.5

Range

18-60

15-42

10-57

IQR

37–44.5

19.5–23

36–44

Fast activity

42%

25%

22%

Deepest sleep stage attained (%)

Awake

Stage 1

Stage 2

Stage 3

Stage 4

DI-EEG, EEG during drug-induced sleep; EEG, electroencephalography; IQR, interquartile range; r-EEG, routine

EEG; SD-EEG, EEG after sleep deprivation.

N r-EEG consisted of a normal recording, including approxi-

mately 3 min of hyperventilation and intermittent photic

stimulation at various frequencies.

N SD-EEG consisted of a recording with the same activation

methods, carried out after a period of outpatient sleep

deprivation. Patients were asked to refrain from sleeping

the evening before the test and to fast from 22:00 h

onwards.

N DI-EEG was recorded 30 min after ingestion of 10 mg oral

temazepam. Where possible, the same activation proce-

dures were undertaken.

beginning treatment; 13 patients failed to complete the

study, undergoing fewer than three EEGs before starting

treatment. Most patients were lost to follow-up, and none

were recorded as having withdrawn consent after seizure

induction.

Characteristics of recordings in each protocol

The stage of sleep attained in each group is shown in table 1.

As expected, more patients attained deeper stages of sleep

after sleep deprivation and to a lesser extent after receiving

temazepam. The duration of recording in each protocol is

shown in table 1. Of the 85 patients who completed the

study, 33 (39%) showed no epileptiform abnormality on any

of their EEG recordings (table 2). In all, 36 patients (43%)

showed generalised spike and wave during at least one EEG

recording, whereas 15 (18%) had a focal discharge evident at

some stage. One patient had generalised slow waves seen on

both SD-EEG and DI-EEG.

Fast-wave changes are an incidental finding more pre-

valent after use of certain drugs including benzodiazepines.

As expected, these were more common in the DI-EEG group.

Each recording was stopped when a patient had completed

hyperventilation, exposure to photic stimulation and sponta-

neously awoken from a period of sleep (if applicable). EEGs

were stored in digital form on CD-ROM. All EEGs were

reported by a consultant in neurology and clinical neurophy-

siology (JPL), who was blinded both to the clinical details

and to the protocol used in each individual recording. EEGs

were reported as being normal or abnormal, with abnorm-

alities defined as the presence of epileptiform abnormalities

in a focal or generalised distribution.

Statistical analysis

Statistical analysis was carried out, where appropriate, on a

PC using V.13.3 of Minitab for Windows. Three-way

comparisons were carried out using x 2

test to assess the

Sensitivity of each recording protocol

In all, 36 patients showed generalised spike and wave

discharges. SD-EEG had a sensitivity of 92% among these

patients, whereas sensitivity of DI-EEG and r-EEG was 58%

and 44%, respectively. Significant difference was observed

between SD-EEG and DI-EEG (p,0.001) and between SD-

EEG and r-EEG (p,0.001) but not on comparing DI-EEG

with r-EEG (p = 0.09).

In one patient, abnormalities were evident on r-EEG but

not on other protocols. In another patient, the only general-

ised discharges seen were during the DI-EEG. In contrast, 10

patients (28%) had their sole changes occurring after a period

of sleep deprivation. The incidence of ‘‘sole abnormalities’’

was significantly higher (p = 0.001) in SD-EEGs than in both

other groups.

Among the 15 patients showing focal discharges, SD-EEG

provoked abnormalities in 73%. r-EEG and DI-EEG each

produced abnormalities in 40% and 27%, respectively. In all, 7

patients (47%) had changes seen only after sleep deprivation.

In 2 patients (13%) the only abnormalities were seen on r-

EEG. In 1 patient (7%), the sole focal change noted was after

drug-induced sleep.

significance.

RESULTS

Demographics

In all, 98 patients were recruited to the study. The median age

of study recruits was 17.9 (interquartile range 15.7–

22.1) years. Eighty five patients completed the study before

Table 2 Electroencephalogram abnormalities with each

protocol among 85 patients completing the study

n (%)

Sensitivity

Paroxysmal spike and wave

36 (43%)

Yield SD-EEG

0.92

Yield DI-EEG

0.58

Yield r-EEG

0.44

Focal

15 (18%)

Yield SD-EEG

0.73

Yield DI-EEG

0.27

Yield r-EEG

0.40

3 normal EEGs

33 (39%)

Risk of clinical seizure occurrence during each

recording method

Two patients had a generalised seizure during at least one of

their recordings. One patient had a generalised tonic–clonic

seizure during SD-EEG, whereas another had a generalised

tonic–clonic seizure during both r-EEG and SD-EEG. No

generalised seizures occurred during DI-EEG. No generalised

Generalised slow waves

1 (1%)

Yield SD-EEG

100.00

Yield DI-EEG

100.00

Yield r-EEG

0.00

DI-EEG, EEG during drug-induced sleep, EEG, electroencephalogram;

r-EEG, routine EEG; SD-EEG, EEG after sleep deprivation.

www.jnnp.com

1042

Leach, Stephen, Salveta, et al

seizures were reported to have occurred after the patients left

the EEG department.

In contrast, using SD-EEG as the preferred protocol would

lead to 100 SD-EEGs being carried out (with around 39

yielding generalised spike and wave). The sensitivity of SD-

EEG would render repeat EEG unnecessary in all but those

cases with remaining strong clinical suspicion of IGE.

Therefore, we can assume that preferred use of r-EEG may

be expected to lead to 81 more EEGs being carried out per 100

EEG referrals than when SD-EEG is preferred. Put another

way, use of SD-EEG as preferred protocol could reduce the

number of EEGs required in young people with new-onset

epilepsy by 45%.

DISCUSSION

The role of EEG in the classification of epilepsies is an

important one; by directing resources, the diagnostic yield

and the confidence in a ‘‘negative’’ result are enhanced, and

the treatment and prognostication of seizure disorders is

thereby improved. This comparison of the yield of each

protocol allows us to ascertain the best way to use resources

by reducing the number of repeat EEGs needed for

classification. In particular, we believe that this study could

help clarify the relative sensitivities of SD-EEG, r-EEG and

DI-EEG.

The age of participants recruited to the study was

important, as EEG is recommended in classification of

epilepsy only in patients with onset before 35 years of age. 1

In this group of young patients, the yield of abnormalities

was as high as expected from other series. 12 This was,

however, less important than the relative yield from each of

the three EEG protocols.

This study suggests that SD-EEG is more likely to elicit

generalised or focal discharges than either of the other two

methods used here. Given the data, lack of generalised spike

and wave on SD-EEG may be enough reassurance that

repeating the EEG will not add more information. DI-EEG

was not as effective as SD-EEG in eliciting either focal or

generalised abnormalities. In fact, pre-dosing with temaze-

pam seems to reduce the incidence of focal discharges,

although this difference did not reach significance. Previous

studies failed to show any difference between drug-induced

sleep and sleep deprivation, 9 but their cohort was already on

treatment for refractory partial epilepsy. Additionally, the

substance used to induce sleep was a barbiturate, which may

have less acute antiepileptic effects than benzodiazepines.

Given its documented hypnotic effects without evidence of

anticonvulsant effects, melatonin (as is used in some

paediatric units to induce sleep for EEG) may be a useful

future comparator.

One explanation for increased yield of epileptiform

abnormalities after sleep deprivation may be a mere result

of repetition of the EEG rather than the inherent usefulness

of SD-EEG. In this study, however, the recordings were

carried out in random order, which would exclude an effect

of order of EEGs and an effect of temporal proximity to the

time of last seizure. The higher incidence of sole abnormal-

ities in the SD-EEG group confirms this as a more sensitive

activation. Although the duration of recording was slightly

longer in SD-EEG (10–60 min) than in the r-EEG (15–

42 min) group, any effect of recording length would be

expected in both SD-EEG and DI-EEG groups; this increase

in duration would not be enough to explain a higher yield of

abnormalities seen only in the SD-EEG group.

The resource implications of the initial use of sleep

deprivation may be considerable: of 100 young patients with

possible new epilepsy, use of r-EEG in the first instance (as is

standard in most units) may be expected to yield 19 patients

showing generalised spike and wave abnormalities. If an

assiduous search for generalised spike and wave is to be

carried out, the remaining 81 would undergo SD-EEG (with

around 21 yielding generalised spike and wave), giving a total

of 181 EEGs performed to fully screen 100 young patients

with possible IGE.

CONCLUSIONS

Outpatient sleep deprivation is an easy and cost-effective way

of enhancing generalised discharges during EEG recording.

There may be some negative aspects of carrying out SD-EEG;

recording times may be slightly longer and there may be a

slightly increased (in this study, non-significant) risk of sleep

deprivation precipitating generalised seizures. Patients

should be made aware of this before giving consent for the

recording. It may be prudent to ensure that anyone with a

history of sleep-deprived seizures undergoes routine EEG as a

first option.

The resource implications of SD-EEG as a preferred

protocol for EEG are considerable and favourable; even

allowing for the increased recording time, and the theoretical

increase in risk of causing generalised seizure activity, there

are benefits to be gained from adopting this protocol.

.....................

J P Leach, L J Stephen, C Salveta, M J Brodie, Epilepsy Unit, Western

Infirmary, Glasgow, UK

Competing interests: None.

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