Introduction
Irish figures estimate that up to 36,000 individuals over the age of five years are affected by epilepsy¹. EEG is a useful investigation, but neurophysiology departments remain a limited resource. To achieve optimal productivity, requests must be appropriate and results of these correctly interpreted. For this reason, we questioned whether or not the NCHDs in our Institution understood the correct indications for EEG, with particular reference to seizure versus syncope and if they could sufficiently interpret certain reports.
Methods
A simple and brief three-stem questionnaire was developed. 179 questionnaires were distributed among the staff of the Hospital before scheduled teaching sessions between July and December 2010. Each question contained a common clinical scenario related to EEG.
Results
Question one involved a 17-year old girl who after a long period of standing, noticed “buzzing” in her ears and a “blackness” coming over her eyes. As she collapses, her friend catches her and notices she is pale and unresponsive. Her eyes are open and her limbs begin to jerk. Once on the ground, she recovers consciousness quickly and is not confused. The question asked was whether or not this girl should be referred for EEG.

Question two reported on a 25-year old man who while sitting at his desk in work, collapses. Witnesses notice he stiffens and develops rhythmic jerking of all four limbs. He becomes cyanosed and the episode lasts approximately 1 minute, with confusion afterwards. An EEG reports “no seizure activity seen” and NCHDs were asked if this meant he did not have a seizure. The final question related to an 80-year old woman admitted to hospital after a collapse and if she should have an EEG ordered before sufficient collateral is obtained. The answer to all three questions was no.  119 questionnaires were returned from 86 interns, 20 SHOs and 13 Registrars. 50% (n=43) of interns, 20% (n=4) of SHOs and 38% (n=5) of Registrars answered question one incorrectly. 4.6% (n=4) of interns, 10% (n=2) of SHOs answered question two incorrectly. All Registrars answered correctly. 8.1% (n=7) of interns answered question three incorrectly. All SHOs and Registrars answered correctly. Overall for question 1, 45% (n=54) answered incorrectly with 5% (n=6) & 6% (n=7) incorrect for question 2 and 3 respectively.
Discussion
Although small, our survey highlighted a number of issues. Although the majority of questions were answered correctly, a substantial number of NCHDs answered question one incorrectly. The focus was on ‘seizure vs. syncope’ and if NCHDs could recognise pertinent facts to determine which was more likely, in this case, vasovagal syncope. Transient loss of consciousness (TLoC) is a common presentation and syncope is much more common than epilepsy, with almost 1 in 2 people suffering a blackout at some stage in life². The ability to recognise the clinical features suggestive of vasovagal syncope was crucial in order to answer this question correctly. These were ‘standing’, ‘buzzing’, ‘blackness’, ‘pale’, ‘recovers consciousness quickly’ and ‘not confused afterwards’. Clinical signs suggestive of a seizure were limb jerks. Despite clues in favour of syncope, the confounding factor was the limb jerking. TLoC regardless of cause can lead to a period of cerebral hypoperfusion and this can manifest as seizure-like activity e.g. myoclonic jerking of the limbs³. A videometric analysis of 56 healthy individuals with induced syncope illustrates this point; 90% of patients who collapsed with a loss of consciousness displayed myoclonic jerking, 79% had additional features such as head turns, automatisms, righting movements and 60% reported either visual or auditory hallucinations⁴. An EEG is not warranted under the circumstances of question one. NICE⁵ advise “an EEG should be performed only to support a diagnosis of epilepsy in adults whom the clinical history suggests that the seizure is likely epileptiform in origin”. These guidelines also state “an EEG should not be performed in the case of probable syncope because of the possibility of a false-positive result.”

Question two addressed the interpretation of EEG reports. “No seizure activity” does not equate to “No seizure”. An audit by Nicolades et al⁶ found that up to 60% of referring doctors believed EEG could diagnose or exclude epilepsy. An EEG has a relatively high specificity (78-98%), but low sensitivity (25-56%) which means a normal result does not out-rule epilepsy⁷. Sensitivity can be influenced by a number of factors. The more EEGs the more likely an inter-ictal discharge (IED) will be captured⁸. Epileptic activity has been captured in 38% of subjects on first testing, but 78% with up to 4 EEG’s⁸. After this, the benefit of was not significant. The sooner an EEG is performed, the more likely it is to be helpful, with most recommending the test within 24 hours of the event⁹. The more frequent a patient has seizures, the more likely an IED will be captured and from this, the number of IEDs may be predictive of seizure recurrence¹⁰. Standard activation procedures such as hyperventilation, photic stimulation and sleep deprivation exist to improve inter-ictal yield¹¹. However, up to 10% of individuals with epilepsy may never have an abnormal inter-ictal EEG⁹.

Finally, question three focused on when an EEG should be requested. In the event of a transient loss of consciousness, every attempt should be made to obtain a clear history from the patient & any witnesses. If epilepsy is strongly suspected from initial observations then an EEG can be useful. Additional indications for EEG include impaired consciousness or altered mental state¹². Seizures may be contributing or the patient may in fact be in non-convulsive status epilepticus. EEG may also demonstrate a functional abnormality when imaging is non-contributory & certain encephalopathies may have particular features on EEG¹³. Requesting an EEG without a suspicion for epilepsy or a suitable alternative indication, make it highly unlikely to aid diagnosis. Non-specific findings or normal variants can add to the uncertainty & ultimately risk a misdiagnosis with both psychological and financial implications¹⁴. NICE¹⁵ released updated ‘Transient Loss of Consciousness’ (TLoC) guidelines in August 2010. They clearly state “do not routinely use EEG in the investigation of TLoC”. As a result of our findings, we set out to educate NCHDs through scheduled Intern teaching & grand rounds. Opportunistic education in the Neurophysiology department is on-going. A further, more in-depth audit of requests for EEG in cases of transient loss of consciousness is warranted to fully assess if NICE guidelines are being met.
Correspondence:  A Laffan
Neurophysiology Department, St. James's Hospital, James’s St, Dublin 8
Email: [email protected] 

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