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Seizure type and seizure syndrome
A community study of children with learning disability9 reflected on the difficulties of
defining seizure type. This was because only 10% of the population with severe physical and
mental handicap underwent electrophysiological tests in this study. The authors showed an
increase in generalised tonic-clonic and myoclonic seizures and a decrease in partial seizures
with increasing handicap and concluded that this increase in generalised seizure disorder was
an artefact of the lack of investigation in this population, though other explanations such as
genetic causes may be valid.

In an institutionalised population Mariani and colleagues5 showed 32.5% of subjects to have
partial epilepsy and 62.5% to have generalised epilepsy, with 5% unclassified. Interestingly,
in the population with generalised epilepsy, 31.4% had EEG changes typical of idiopathic
epilepsy. Unfortunately further data on seizure type or syndromal diagnosis in these patients
was not given. It seems from these two sources that generalised abnormalities, and hence
appropriate treatment options, should not be unexpected in people with learning disability.

Assessment

Aetiological factors
Learning disability is caused by a range of pathological processes, as of course is epilepsy
itself. The underlying cause of the learning disability has an impact on seizure type and
outcome.

Epilepsy phenotypes
The seizure disorder associated with some conditions, for example tuberous sclerosis10, has
been well defined. In the case of tuberous sclerosis the value of a good epidemiological
survey was shown with a lower than expected prevalence of learning disability in the
condition than previously recognised. The nature of epilepsy in Down syndrome has been
characterised11. A seizure disorder is often associated with Alzheimer’s disease, particularly
if onset occurs over 30 years of age. This obviously has a significant impact on the outcome
of new onset epilepsy in this age group.

For some other conditions associated with disability, such as the fragile X syndrome, epilepsy
conditions specific to the syndromes have been suggested. In the case of fragile X there are
reports that a specific EEG abnormality similar to benign childhood epilepsy with centro-
temporal spikes is present12 although controversy remains over the validity of this finding 
possibly due to sampling and other methodological issues13. Table 2 summarises these
epilepsy phenotypes1012,14. Rett syndrome poses a specific challenge. The condition is
associated with high levels of epilepsy, possibly as a result of the frequently severe level of
intellectual disability. However the condition can also offer diagnostic challenges with the
frequent hyperventilation and other autonomic disturbances being misdiagnosed as partial or
other seizure types.

Other impairments
The association between the likelihood of having epilepsy if an individual has an additional
impairment is strong. Hauser and colleagues15 showed an increase in the risk of epilepsy from
11% to 48% when a child with learning disability also had cerebral palsy  an association
confirmed by others16. Steffenburg and colleagues6 showed a prevalence of cerebral palsy of
14% and 59% respectively in the mild and severe groups of patients with learning disability
and epilepsy. In the population with learning disability who had epilepsy the risk of additional
impairment was 3% in the population with mild disability and 37% in those with severe
disability.