• epilepsy
• eeg

A young woman with depression was referred for evaluation of refractory stereotypical seizures. These started 12 months before, manifesting as a brief feeling of panic and strange abdominal sensation (‘fluttering’), followed by an apparently minimally responsive ‘dreamy’ state lasting around 20 min.

The initial suspicion of temporal lobe epilepsy was strengthened by a subsequently requested sleep-deprived electroencephalography (EEG), reported elsewhere as showing ‘frequent runs of sharp activity over the temporal regions supporting a focal seizure disorder’. She subsequently tried three different antiepileptic medications (carbamazepine, then levetiracetam, then levetiracetam and sodium valproate) with no improvement and then increasingly frequent events. MR scan of brain was normal.

Ambulatory EEG captured several stereotypical clinical attacks during which the EEG remained normal. However, as she became drowsy during the recording, there were repeated runs of prominent bitemporal sharp waves (figure 1). Their fixed monomorphic, monorhythmic and non-evolving character allowed them to be recognised as a benign EEG pattern rather than temporal lobe seizure activity. Their topographical location and occurrence in drowsiness are typical of ‘rhythmic temporal theta burst of drowsiness’. Despite its impressively sharp activity, this EEG variant is benign. It occurs most commonly in young adults and is not associated with epilepsy.1 The patient improved dramatically following a revised diagnosis of dissociative seizures, antiepileptic drug withdrawal and cognitive behavioural therapy. Figure 2 shows a temporal lobe epileptic seizure recorded from another patient for comparison.

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Figure 1

EEG from this patient. Runs of bitemporal sharp waves (asterisks); distinguished from epileptic seizure activity by their monomorphic, monorhythmic and non-evolving characteristics. An EEG clue to her drowsy state is the slow roving eye movement artefacts (arrows).

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Figure 2

An EEG illustrating a right temporal lobe epileptic seizure recorded from another patient for comparison. Note the evolving change in morphology and amplitude of sharp activity from the onset (asterisk) as well as fluctuations in the rhythmic frequency and spread of sharp activity as the seizure progresses (from left to right).

Epilepsy remains primarily a clinical diagnosis; the EEG can help in further evaluation of patients with suspected seizure disorders, although not without its potential pitfalls. About one-third of patients with refractory seizures admitted for EEG-video monitoring have been previously misdiagnosed, and the overinterpretation of sharpened activity in normal EEGs is an important reason for this.1

Neurologists and neurophysiologists will be familiar with terminology including sharp waves, spikes, polyspikes and spike-and-slow waves. The hallmark of such EEG abnormalities serving as markers of epileptogenesis, or a predisposition to seizures, is their sharp nature. Importantly, physiological sharp activity with no connotations to epilepsy may also occur. Some are easily recognisable such as vertex sharp waves in sleep; other less common sharp variants may be more challenging to identify correctly as benign, particularly if they manifest as runs of ‘rhythmic temporal theta bursts of drowsiness’, as in this patient.1 Recognising these benign variants and applying published criteria required to fulfil EEG definitions of ‘epileptiform’2 will help to distinguish physiological from pathological sharp activity.

Misdiagnosis of epilepsy may carry life-long consequences, making it particularly important that all EEG sharp transients or patterns are not automatically assumed to signify an epileptiform abnormality.