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Epileptic Disorders

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Idiopathic generalised epilepsy with phantom absences and absence status in a child Volume 3, issue 2, June 2001

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  • Idiopathic geenralised epilepsy with phantom absences and absence status in a child

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We have recently described an idiopathic generalised epilepsy syndrome with phantom absences of undetermined onset that first becomes apparent in adulthood with generalised tonic clinic seizures (GTCS) and frequently, absence status epilepticus [1, 2]. Other authors have subsequently reported similar cases [3, 4]. The intriguing feature of this syndrome is that all patients have typical absence seizures, which are so mild that they are inconspicuous to the patient and imperceptible to the observer (phantom absences). Patients and relatives are unaware of them. Phantom absences are usually first discovered during video-EEG recordings with breath counting during hyperventilation [1, 5-7]. Characteristically, counting slows down and the patient may make errors during generalised 3-4 Hz spike or polyspike-slow wave discharges. About half of the patients have mild eyelid fluttering (not eyelid myoclonia), often with partial opening of the eyes as the only visible manifestation during these discharges [1]. Relatives retrospectively recall similar brief episodes of eyelid fluttering "for many years" prior to the first overt clinical convulsive seizure and the patients retrospectively recognize having had brief episodes of "loss of concentration". Absence status ending with GTCS or GTCS alone, without other perceived seizures is the first conspicuous, clinical manifestation. Similar cases have not been previously reported in children.

We present a normal 11 year-old girl who had had 6 episodes of absence status epilepticus starting at age 10 years. Video-EEG documented numerous typical absence seizures, the occurrence of which were totally unsuspected by either the child or her parents.

Case study

Our patient was born after a normal pregnancy and delivery in 1989. Her subsequent neurodevelopment was normal. She is highly intelligent and the top in her class. Her maternal grandfather had a possible single seizure but no other details are known.

In a nine-month period when aged 10 years she had six episodes of absence status epilepticus lasting for many hours. During these she was reported as quiet, disorientated and confused. At the end of each she felt drowsy, slept and then awoke with no recollection of the preceeding events but was otherwise entirely normal. She has never had a convulsion.

Her mother gave a vivid account of the episodes: "It seems to start with her just being quiet and subdued for a couple of hours or more but still being able to understand whatever is going on and subsequently she becomes confused and unable to understand. Almost like sleepwalking, her eyes are open and she wanders around apparently normally (co- ordination and movement are normal) but when you talk to her, although she looks at you and maybe even says she understands or nods, you can see that nothing is registering. The expression that springs to mind is 'the lights are on but there's nobody in'."

In the first absence status "She was tired in the morning having had 3 consecutive late nights. We did a 4-mile walk with a group of people that she knew. She was very quiet and did not mix in with the other people as would normally but when asked she said she was fine. She did not want any lunch ­ very unusual for her ­ and still very quiet. She was asked to unload the dishwasher ­ job she was used to doing, but she kept taking the dishes out and then trying to put them straight back in again. We made a joke of it to start with but she seemed unable to understand that she was doing anything wrong... It was almost as though she was in a trance, like being half asleep but with her eyes open. She has never been a sleepwalker but this was the appearance that she gave... She went to bed at 2pm (without protest ­ normally unknown even when she is ill) and slept all afternoon and evening until the next morning when she was perfectly OK and went to school." On other occasions, "while on a school excursion, she became confused, disorientated and ended up putting on other children's clothes when getting ready to go out for the evening". "She was very tired after a week of a bad cold and not sleeping well. She had had a long and busy day... She was very quiet and withdrawn but wouldn't go to sleep. Later in the day she became confused and again unable to follow simple instructions. We asked her to go and have a shower or bath. I followed her a few minutes later and she was cleaning her teeth. I reminded her about the shower and although she said OK, she then went back and cleaned her teeth again, put the brush and paste away, wiped her mouth on the towel and then went and repeated this a third time. When I pointed out to her that she had already done this she didn't seem to register what I was saying and then went back and tried to clean her teeth yet again."

There were no recognizable precipitating factors to these episodes other than sleep deprivation and fatigue. Detailed enquires have failed to reveal any suggestion of absences or any other type of seizure even after demonstrating the video-EEG events. "We have never seen any evidence of convulsions, fits, twitching or eyes rolling or flickering."

High resolution MRI was normal but on video EEG there were frequent, spontaneous and hyperventilation-induced absence seizures of 2- 6 sec duration (video and figure 1). Clinically these manifested with interruption of counting, eyelid fluttering and partial opening of the eyes. There was a mild atonic component revealed when she was asked to hold her arms outstretched. The ictal EEG showed generalised discharges of spike, multiple spike and slow waves at around 3-4 Hz (figure 1). In addition, there were frequent, brief interictal multifocal bursts of spikes or multiple spikes (figure 2), which we interpret as abortive generalised discharges.

Following the video-EEG, treatment with sodium valproate 200 mg bd was started. No further clinical events occurred. Because of weight gain, valproate was substituted for lamotrigine 10 mg bd. She has remained seizure-free. Video-EEG at 6 and 10 months after onset of treatment were practically normal.

Discussion

There is little doubt that this girl has idiopathic generalised epilepsy. A video-EEG unequivocally revealed typical absence seizures, which were frequent but so mild as to escape recognition, even by her parents. In this context, it is reasonable to propose that her prolonged episodes of confusion were caused by absence status epilepticus. Her excellent response to appropriate treatment supports this diagnosis. The question is: what type of idiopathic epilepsy with typical absence seizures does she have?

There are 4 generalised epilepsies associated with typical absence seizures currently recognized by the Commission of the International League Against Epilepsy (ILAE) [8]: Childhood absence epilepsy [9], juvenile absence epilepsy [10-12], myoclonic absence epilepsy [13] and juvenile myoclonic epilepsy [14-16].

Childhood and juvenile absence epilepsy, by definition, manifest with absence seizures, which are obvious, often prolonged, severe and disturbing [8-13]. This is not the case here. Also, many consider absence status as an exclusion criterion for childhood epilepsy [2, 6, 9, 17]. Absence status is probably exceptional in myoclonic absence epilepsy [13] and has not been described as a first clinical manifestation of juvenile absence epilepsy [2, 6, 7, 17].

Juvenile myoclonic epilepsy starting with absences in childhood is a possibility [14-16]. In this syndrome, absences, like those of this girl, are mild and inconspicuous [16, 18]. However, absence status is reported [19], but is exceptional as an initial clinical manifestation [14-16]. When it occurs, it is mainly of a myoclonic type. Furthermore, eyelid fluttering, a constant component of this girl's absences, is an uncommon feature in the absences of juvenile myoclonic epilepsy. However, exceptions are the rule in medicine and although unlikely, this diagnosis can not be excluded in this case without further follow-up.

Of other relevant proposed syndromes of idiopathic generalised epilepsy with absence seizures, eyelid myoclonia with absences [20] must also be considered. In eyelid myoclonia with absences, the eyelid myoclonia is marked and the predominant symptom. It often occurs alone without absences and is mainly precipitated by eye-closure and photic stimulation [20, 21]. None of these are relevant to this case.

Perioral myoclonia with absences [22] or typical absence seizures with single myoclonic jerks [6, 7] are excluded by the lack, in this case, of the relevant ictal clinical manifestations (perioral myoclonia and single myoclonic jerks respectively) on both video-EEG and clinical history [6, 7].

The closest syndromic diagnosis we can suggest is the syndrome recently described with phantom absences, infrequent generalised tonic clonic seizures and absence status [1-4, 7]. Although the youngest patient previously reported with this syndrome was 17 years old at the onset of clinically evident seizures, in most epilepsy syndromes seizure, threshold and age-at-onset vary considerably. "Phantom absences" have only recently been recognised [1-4]. Video-EEG with breath counting during generalised discharges of spike and slow waves has only recently begun to be used as a diagnostic tool in epilepsies [5, 7, 17, 18]. There are many patients who do not fit within the syndromes recognised by the Commission of the ILAE. Patients and parents are anxious to know prognosis, genetics and long-term management. Reporting of such cases may help delineate new syndromes and allow better understanding and prognosis.

Videotape legend

During a 45 minutes recording there were 12 absences during hyperventilation, 4 spontaneous and one occurred only once at 60 Hz IPS. They all lasted for 2-6 sec.

The video shows seven absences. All occurred during hyperventilation except the 4th and 5th that are spontaneous.

Onset and end of the EEG discharges is as follows:
1st absence from 11:17:44 to 11:17:49
2nd absence from 11:22:23 to 11:22:27
3rd absence from 11:23:20 to 11:23:25
4th absence from 11:25:12 to 11:25:15
5th absence from 11:25:28 to 11:25:31
6th absence from 11:43:17 to 11:43:23
7th absence from 11:43:58 to 11:44:01

CONCLUSION

Received February 5, 2001 - Accepted April 24, 2001