Assessing the risk of subsequent tonic-clonic seizures in patients with a history of simple or complex partial seizures.

BACKGROUND: Patients who present with only simple or complex partial seizures have a poorly documented prognosis. Treatment may be advocated to prevent future secondary generalised seizures, reduce the frequency of further simple or complex partial seizures or a combination of both. METHODS: A full statistical analysis on 1334 patients was carried out. The outcomes measured were post-randomisation times to first seizure of any type and first tonic-clonic seizure. Methodology was adopted that accounted for individuals' underlying pre-randomisation seizure counts and allowed for the possibility that there may be a proportion of the sample that will not experience post-randomisation seizure recurrence. RESULTS: 103 subjects randomised to the MESS (Multicentre Study of Early Epilepsy and Single Seizures) study had only partial seizures at randomisation. Only 17 of these had a tonic-clonic seizure during follow-up. The presence of an abnormal EEG at randomisation influenced this risk: an estimated 23% of those with EEG abnormality were at risk of tonic-clonic seizures during follow-up compared with 16% of those with a normal EEG. The group did, however, continue to have partial seizures during follow-up, and modelling showed that the impact of treatment on these seizures was significantly less than the effects of treatment on the frequency of tonic-clonic seizures in those patients with such pre-randomisation seizures. CONCLUSION: Patients presenting with a history of only partial seizures are at low risk of subsequent tonic-clonic seizures in the period of time to which therapeutic decisions are relevant. The effects of the antiepileptic drugs used in the MESS study are greater for tonic-clonic seizures than they are for partial seizures.