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Diagnosis and differentials

Diagnosis of TA in children with severe ictal impairment of consciousness is relatively
easy. Their brief duration with abrupt onset and termination, high daily frequency, and
nearly invariable provocation with hyperventilation makes them one of the easiest types of
seizures to recognise. The child with suspected TA should be asked to overbreathe for three
minutes, counting his or her breaths while standing with hands extended in front;
hyperventilation will provoke an absence in more than 90% of those who suffer. We
recommend that this test should also be undertaken in suspected adults, in whom TAs are
usually mild and may be missed. Misinterpretation of TA for partial seizures (focal motor
in the case of regional asymmetric ictal myoclonic components, or complex partial – limbic
– when ictal automatisms, such as perioral, swallowing, fumbling are present) may
seriously affect management and treatment. The basic clinical criteria for differentiating
TA from complex partial seizures are given in Table 2. The clinical approach needs to be
complemented by (preferably video) EEG studies, ideally prior to commencing treatment.
An EEG would confirm the diagnosis of TA in more than 90% of these untreated children
with ictal recordings mainly during hyperventilation. If not, the diagnosis of absences
should be questioned48. In addition, ictal video-EEG documentation may reveal features
favouring a specific epileptic syndrome and assist in determining long-term prognosis and
management. The fundamental EEG differences between TA and complex partial seizures
are also shown in Table 2.

Diagnosis of other co-existent seizure types, and definition, if possible, of the electroclinical
syndrome as outlined in the previous section is the final diagnostic step before initiating
treatment. Symptomatic absences in non-lesional frontal lobe epilepsy are often impossible
to distinguish, especially in the absence of partial seizures45. Cerebral cortical dysgenesis is
usually detectable on brain MRI46. Such symptomatic/cryptogenic absences are very rare.
Finally, TA in IGE can be easily differentiated from atypical absences that occur only in
the context of mainly severe symptomatic or cryptogenic epilepsies in children with
learning difficulties and frequent seizures of other types, such as atonic, tonic, and
myoclonic seizures.

Treatment

General principles
Prognosis is syndrome-related. For instance, childhood absence epilepsy is a relatively
benign syndrome, which usually remits within 2–5 years from onset. In all other IGE
syndromes there is probably a life-long liability to TA, myoclonic jerks, and GTCS. Poor
initial response to treatment49,50 and photosensitivity49 may be of adverse prognostic value
for long-term remission of seizures. Repeat EEG is particularly useful in monitoring the
response to treatment as there is a very close correlation between control of clinical
absences and electrographic abnormalities51,52; such a relationship does not exist in other
generalised seizures (tonic-clonic or myoclonic), or in partial epilepsies.

Planning of management and appropriate advice and counselling is therefore possible once
a confident syndromic diagnosis has been established, or at least the question of possible
photosensitivity or other reflex activation, and the co-existence of myoclonic jerks, GTCS
or both has been answered satisfactorily. Currently, sodium valproate, ethosuximide and
lamotrigine, alone or in combination, are the only first-line agents for TA. Choice between
them depends on other co-existent generalised seizures, and – obviously – adverse
reactions. Table 3 presents the proposed steps in the therapeutic process that targets TA in
different clinical patterns.