Page 153 - ILAE_Lectures_2015

4) Rarer seizure types include: seizures characterised by brief lapses of awareness, which
are mainly seen with anterior mesial frontal seizures, frontopolar or orbitofrontal
seizures; in addition, akinetic seizures, aphasic seizures or seizures characterised by
early head version without loss of awareness.

Spread of seizure discharges may occur very rapidly between the hemispheres, resulting in
sudden hypertonia, or less frequently hypotonia, causing drop attacks with severe injury. The
seizure may: a) continue in the same phase on the ground, b) progress to a generalised clonic
seizure, or c) there may be rapid recovery.

Electroencephalography

Inter-ictal EEG recordings are often challenging and it has been reported that up to 40% of
patients with FLE do not have inter-ictal epileptiform discharges. The yield of prolonged
video EEG recordings and careful review of EEG samples with closely spaced midline
electrodes may be of higher yield. Ictal scalp recording of EEG changes in FLE is hampered
by the size of the frontal lobes, which means that signals from distant, mesial or deep gyral
discharges may be attenuated and undetectable8, 9. Where detected, the spatial resolution and
discharge localisation is often very poor. As motor manifestations are prominent, often
without any aura, ictal scalp EEG recording is often swamped by muscle artifact and thus
uninterpretable. Post-ictal EEG suppression may be very short. Localisable ictal EEG
changes were found in 3040% of cases.

Intracranial EEG recordings using subdural grid electrodes and/or depth electrodes may be
necessary in lesional cases where exact delineation of extent of epileptogenicity is necessary,
in addition to allowing for mapping of eloquent cortex using cortical stimulation. In non-
lesional cases invasive EEG can be undertaken if there is a clear hypothesis of the ictal onset
zone. However, intracerebral studies suffer from sampling error, only detecting discharges
that are very near the electrodes. Without accurate information to guide electrode placement,
this too is often unsuccessful.

Imaging

Even in refractory FLE the detection rate of imaging is poorer than in temporal lobe epilepsy
(TLE)9. Computed tomography identifies abnormalities with localising value in about 20%
of cases and magnetic resonance imaging in a further 3040%. Positron emission tomography
frequently shows abnormalities but these are commonly rather non-specific. As magnetic
resonance imaging becomes more sensitive, small areas of dysplasia and heterotopia are
increasingly detected; their clinical significance remains to be evaluated. The size of the
frontal lobes means the location of the lesions responsible for FLE is more variable than for
TLE.

Frontal versus non-epileptic seizures

It has been recognised that some seizures previously labelled as non-epileptic are in fact due
to FLE. The reasons for the confusion include:
 Motor activity in FLE is frequently bizarre and complex.
 Bilateral motor activity may occur in FLE with partial preservation of awareness.
 The inter-ictal EEG may be normal and the ictal changes obscured by artifact.

There are some differentiating features: epileptic seizures are often stereotyped for an
individual, shorter and commonly occur from sleep. Caution should be exercised in
diagnosing seizures arising purely from sleep as being non-epileptic. An earlier age of onset