The diagnostic value of the short sleep EEG and other provocative methods following sleep deprivation

Seizure provocation in EEG recordings: A data-driven approach

OBJECTIVE

Recording seizures on video-EEG has a high diagnostic value. However, bilateral convulsive seizures constitute a risk for the patients. Our aim was to investigate the diagnostic yield and associated risks of provocation methods in short-term video-EEGs.

METHODS

We extracted data on seizures and provocation methods from a large database of short-term video-EEGs with standardized annotations using SCORE (Standardized Computer-based Organized reporting of EEG).

RESULTS

2742 paroxysmal clinical episodes were recorded in 11 919 consecutive EEGs. Most epileptic seizures (54%) were provoked. Hyperventilation provoked most of typical absence seizures (55%), intermittent photic stimulation (IPS) provoked myoclonic seizures (25%) and most of bilateral convulsive seizures (55%), while 43% of focal seizures were precipitated by sleep. All but one of the 16 bilateral convulsive seizures were provoked by IPS or sleep. Latency between start of generalized photoparoxysmal EEG response and bilateral convulsive seizures were ≤3 s in all but one patient.

SIGNIFICANCE

The large, structured database provides evidence for the diagnostic utility of various provocation methods in short-term video-EEGs. The risk of bilateral convulsive seizures is relatively small, but it cannot be prevented by stopping IPS after 3 s. A priori knowledge about seizure semiology helps planning patient-tailored provocation strategy in short-term video-EEGs.

Cycles in epilepsy

Epilepsy is among the most dynamic disorders in neurology. A canonical view holds that seizures, the characteristic sign of epilepsy, occur at random, but, for centuries, humans have looked for patterns of temporal organization in seizure occurrence. Observations that seizures are cyclical date back to antiquity, but recent technological advances have, for the first time, enabled cycles of seizure occurrence to be quantitatively characterized with direct brain recordings. Chronic recordings of brain activity in humans and in animals have yielded converging evidence for the existence of cycles of epileptic brain activity that operate over diverse timescales: daily (circadian), multi-day (multidien) and yearly (circannual). Here, we review this evidence, synthesizing data from historical observational studies, modern implanted devices, electronic seizure diaries and laboratory-based animal neurophysiology. We discuss advances in our understanding of the mechanistic underpinnings of these cycles and highlight the knowledge gaps that remain. The potential clinical applications of a knowledge of cycles in epilepsy, including seizure forecasting and chronotherapy, are discussed in the context of the emerging concept of seizure risk. In essence, this Review addresses the broad question of why seizures occur when they occur.

Under-sampling in epilepsy: Limitations of conventional EEG

The cyclical structure of epilepsy was recently (re)-discovered through years-long intracranial electroencephalography (EEG) obtained with implanted devices. In this review, we discuss how new revelations from chronic EEG relate to the practice and interpretation of conventional EEG. We argue for an electrographic definition of seizures and highlight the caveats of counting epileptiform discharges in EEG recordings of short duration. Limitations of conventional EEG have practical implications with regard to titrating anti-seizure medications and allowing patients to drive, and we propose that chronic monitoring of brain activity could greatly improve epilepsy care. An impending paradigm shift in epilepsy will involve using next-generation devices for chronic EEG to leverage known biomarkers of disease state.

Controversial issues on EEG after sleep deprivation for the diagnosis of epilepsy

EEG after sleep deprivation (SD-EEG) is widely used in many epilepsy centers as an important tool in the epilepsy diagnosis process. However, after more than 40 years of use, there are a number of issues which still need to be clarified concerning its features and role. In particular, the many scientific papers addressing its role in epilepsy diagnosis often differ remarkably from each other in terms of the type of patients assessed, their description and study design. Furthermore, also the length and the type of EEG performed after SD, as well as the length of SD itself, vary dramatically from one study to another. In this paper we shortly underscore the abovementioned differences among the different reports, as well as some interpretations of the findings obtained in the different studies. This analysis emphasizes, if needed, how SD-EEG still represents a crucial step in epilepsy diagnosis, and how additional, controlled studies might further shape its precise diagnostic/prognostic role.

Sleep deprivation activates epileptiform discharges independent of the activating effects of sleep

An electroencephalogram (EEG) recorded after sleep deprivation (SDEEG) in epilepsy patients often discloses epileptiform discharges (ED) when routine EEG (REEG) does not, but since sleep alone activates ED, activation during SDEEG may result merely from the induction of sleep. We retrospectively investigated whether SDEEG is useful when REEG containing wakefulness and sleep fails to show ED. Subjects were patients with definite or highly probable epilepsy whose REEG lacked ED and who later underwent SDEEG. All had wakefulness and at least stage II sleep during both REEG and SDEEG. Patients with ED on REEG were specifically excluded to avoid including patients with activation due merely to the occurrence of sleep. Patient and EEG characteristics were studied, including duration of wakefulness and each sleep stage and timing and characteristics of ED. Fifteen of 29 patients (52%) had activation on SDEEG; exclusively during wakefulness in 1, exclusively during sleep in 6 and in both wakefulness and sleep in 8. Activation rates were not significantly different between wakefulness (9, 60%), stage I (11, 74%) and stage II (11, 74%). EEG characteristics were similar for REEG and SDEEG, except that total EEG duration and stage II sleep were longer in SDEEG than in REEG, which did not influence activation by a logistic regression model (p > 0.05). We conclude that sleep deprivation activates ED independent of the activating effects of sleep and therefore is useful in evaluation of suspected epilepsy even when REEG contains sleep.

The diagnostic yield of a second EEG after partial sleep deprivation: a prospective study in children with newly diagnosed seizures

PURPOSE

To assess the diagnostic yield of a repeated EEG (REPEEG) after partial sleep deprivation (SD) in children and adolescents with one or more seizures who previously had had a standard EEG (STDEEG) without epileptiform abnormalities (EAs). In the literature, 32-75% of such REPEEGs after SD were reported to show EA.

METHODS

In a prospective, multicentred study, we selected children aged 1 month to 16 years with one or more idiopathic or remote symptomatic newly diagnosed seizures. A REPEEG was recorded in children without EAs in their STDEEG.

RESULTS

Of 552 children and adolescents who entered the study, 243 (44%) had a STDEEG without EAs. In 177 (73% of eligible children), REPEEGs were recorded after SD. We found EAs in 61 (34.5%) REPEEGs and new nonepileptiform abnormalities in five (1%). In 552 children in the total cohort, the REPEEG thus added 11% with EAs to the 56% with EAs in the STDEEG. Of REPEEGs, 81% included sleep compared with 20% of STDEEGs. In about half the REPEEGs, EAs occurred during sleep only. One child had tonic-clonic seizures probably related to the SD.

CONCLUSIONS

One third of REPEEGs yielded new diagnostic information. Partial, age-dependent SD was highly effective in inducing sleep, which is important because in many cases EAs were found only during EEG recording in sleep. The procedure was safe and convenient.

The effect of sleep deprivation on the rate of focal interictal epileptiform discharges

Eight men with complex partial seizures who had frequent focal interictal epileptiform discharges (FIEDs) during routine EEGs were selected for all-night EEG recording before, and after 36 h of sleep deprivation. After sleep deprivation 6 of 8 patients showed increased FIEDs. The pooled mean number of FIEDs was greatest during light non-REM stages of sleep, especially stage II. Thus sleep deprivation is an effective activation method in medicated patients with complex partial seizures. However, a significant activation requires recording stage II sleep after sleep deprivation.