Investigations and diagnosis

Investigations and diagnosis

Questions from healthcare professionals

Q: Where can I find information on epilepsy and hypnagogic or hypnapompic hallucinations?

A: These events are generally seen on sleeping and/or waking and would suggest a possible diagnosis of narcolepsy. To find information on them in relation to epilepsy, you might like to research on the PubMed website at http://www.ncbi.nlm.nih.gov/pubmed
Answered by Epilepsy Society's medical team
June 2011

Q: I am interested in the case of a child with congenital adrenal hyperplasia. The child experience episodes of blankness and unresponsiveness followed by period of disorientation. The episodes are not linked to any physical ill health. The child is on treatment including steroids and sodium replacement. They did have febrile seizures as an infant but no further convulsive seizures have been observed. If these episodes are seizures, is it likely to be non epileptic seizures linked to metabolic or hypoglycaemia?

A: The crucial point is to get an accurate and complete diagnosis. It would be advisable for the children to be seen by a paediatric neurologist, and considered for a prolonged video-EEG, with the possibility of simultaneous blood sampling at the time of any episodes, for glucose levels.
May 2010

Q: What is it useful to record during a seizure?

A: It is useful to note as much as possible about the lead up to, the seizure itself, and the recovery period afterwards. The recording information about seizures page on Epilepsy Society's website has a list of useful things to look out for, and record, during a seizure.
May 2010

Q: What are the differential diagnoses for loss of consciousness and convulsions?

A: Please see our differential diagnosis articles page on this website, which includes chapters on non-epileptic paroxysmal neurological and cardiac events and the diagnosis and management of dissociative seizures.
May 2010

Q: What methods can be used to differentiate between epileptic and non-epileptic seizures?

A: There are several chapters in the articles section on this site that may be of interest. Under Differential diagnosis there are chapters on Fits, faints and funny turns - the differential diagnosis of epilepsy and Diagnosis and management of dissociative seizures. 
May 2008

Q: Can a child with a prolonged complex partial seizure still have a normal EEG?

A: This would depend on whether the EEG recorded brain activity during the seizure itself (ictal EEG) or not during the seizure (inter-ictal EEG). For more information about the use of EEGs see the chapter Neurophysiological investigation of epilepsy in our articles section.
February 2008

Q: What percentage of normal population and of patients with epilepsy have the spike-slow wave complex epileptiform abnormality?

A: A very small number, probably less than 1%, and usually siblings of people with idiopathic generalised epilepsies.
November 2007

Q: Is there anything to be gained by classifying seizures? Other than for prescribing medication & getting an overall view of how badly children are affected by seizures is there any reason for recording subtle differences?

A: Accurate seizure classification is important to detect changes in pattern and to communicate with other professionals about the person's seizures.
November 2007

Q: Can you advise if someone who has suspected epilepsy, but is awaiting diagnosis can still drive?

A: The general recommendation would follow the DVLA regulations that if epilepsy is suspected, a person should not drive until the diagnosis has been confirmed or refuted.
October 2007

Q: In a person with a controlled temporal lobe seizure disorder, what does focal slowing and frequent sharp waves on the EEG mean?

A: The pattern on the EEG isn’t influenced by seizure control or treatment. For more information on EEGs, please see the article Neurophysiological investigation of epilepsy, which is in the  articles section on this site.
November 2006

Q: What is the best drug to administer to a patient to limit their movement during EEG, in order to record ictal discharges during complex partial status epilepticus?

A: No drug should be used as it may alter the EEG.
November 2006

Q: How can we prove that what has been recorded as a fit was not a fit but a faint?

A: It is not possible to prove afterwards, whether an event was a seizure (fit) or not. Having a very detailed description of what happened before, during and after the event may indicate the most likely cause. There is more information about diagnosis on this website in Library of articles – Investigations and Diagnosis.
December 2005

Q: How long after a suspected seizure do prolactin levels remain elevated and can this realistically be used to differentiate between epilepsy and non-epileptic seizures?

A: Prolactin levels are not reliable for differentiating between epileptic and non-epileptic seizures. They remain elevated for no more than 20 - 30 minutes.
August 2005

Q: What is the methohexitol suppression test?

A: The methohexitol suppression test is used to suppress the EEG in certain conditions. The most common situation is in Landau Kleffner syndrome where there are often severe bilateral EEG changes. Methohexitone supresses the EEG and then the EEG is recorded as the methohexitone wears off. When the EEG returns, in some cases it returns first on the side and in the area most severely affected and this can be a guide for surgery.
April 2005

Q: In your article ‘Stopping anti-epileptic drug treatment’ you say regarding the value of persisting EEG abnormalities in seizure-free patients 'In children there seems little doubt that the presence of persisting EEG abnormalities has an adverse prognostic influence but whether this is true in adults remains uncertain'. Does the type of these abnormalities make a difference i.e. whether they are focal or generalised?

A: Not focal discharges but clear-cut epileptiform generalised discharges are a contraindication to the withdrawal of AED as they are predictive of recurrence. This only applies to children.
February 2005

Q: Are there any non-invasive techniques to determine the focus/origin of a seizure if it is deep inside the brain and surface electrode EEG measurements do not have sufficient resolution to discriminate the origin?

A: No non invasive technique is routinely used.
September 2004

Q: Can clinically-diagnosed non-convulsive status epilepticus with impaired level of consciousness be accompanied by normal EEG?

A: If the EEG was entirely normal, this would not be compatible with a diagnosis of non-convulsive status. However, the EEG may show only non-specific abnormalities, such as theta or delta rhythms, in non-convulsive status - the presence of epileptiform activity is not essential for diagnosis, except in the absence type associated with generalised spike wave discharge. There are no widely accepted criteria for EEG diagnosis of non-convulsive status, but most authorities would accept rhythmical non-epileptiform or epileptiform activity, occurring either as discrete seizure-like events, or continuously, which is attenuated or abolished by appropriate anti-epileptic medication.
March 2004

Q: Are there any national guidelines as to an acceptable wait for routine EEG after a request has been made?

A: The National Sentinel Clinical Audit of Epilepsy-Related Death (2002) recommended that new cases of suspected epilepsy have EEGs within four weeks. The Association of British Neurologists also has recommendations for the timing of various investigations.
March 2004

Please note: Epilepsy Society is unable to provide a medical opinion on specific cases. Responses contain information relating to the general principles of investigation and management. Answers are not, and should not be assumed to be, direct medical advice.