Hippocampal damage caused by seizures in temporal lobe epilepsy

Abstract

Tuuli Salmenperä and colleagues (Jan 3, p 35)1Salmenperà T Kàlviàinen R Partanen K Pitkànen A Hippocampal damage caused by seizures in temporal lobe epilepsy..Lancet. 1998; 351: 35Summary Full Text Full Text PDF PubMed Scopus (53) Google Scholar suggest that hippocampal damage is caused by seizures in temporal lobe epilepsy (TLE), and that, therefore, good seizure control may be neuroprotective. We wholeheartedly agree that every effort should be made to control seizures, but wish to raise some points about the methodology. How were the controls chosen and matched? In the investigators' reference to hippocampal volume measurement, it is stated that for statistical calculations, measurements of hippocampal volume are “normalised” by division by brain area measured in a coronal plane “at the level of the anterior commissure”. The choice of plane is unspecified (rotation of a coronal plane through this landmark, can make the plane axial!), which could affect the correction made. Published cases of rapid volume loss after status epilepticus and subsequent chronic seizures exist;2Weishmmann UC Woermann FG Lemieux L et al.Development of hippocampal atrophy: a serial magnetic resonance imaging study in a patient who developed epilepsy after generalised status epilepticus..Epilepsia. 1997; 38: 1238-1241Crossref PubMed Scopus (115) Google Scholar there are cases with longstanding apparently typical TLE without any loss of hippocampal volume. Hippocampal-volume loss is a single change, as seen on magnetic-resonance imaging, but may be heterogeneous in aetiology and effect. Without the support of histology (were any patients offered surgical treatment?), cross-sectional analysis may obscure pathological subtleties that need exploration. Thus, in their own group, the patients with the longest duration of TLE and “damage” were more likely to have begun their seizures at age 5 years or younger. It could be argued that these patients do not have the variety of TLE most commonly seen in adults with refractory partial seizures, in which group habitual seizures frequently follow a quiescent period after an initial injury.3Engel Jr, J Update on surgical treatment of epilepsies..Neurology. 1993; 43: 1612-1617Crossref PubMed Google Scholar The cross-sectional design of the study does not exclude the possibility that those patients with the longest duration of epilepsy had the most severe loss of hippocampal volume before the onset of habitual epilepsy and had the most refractory epilepsy. Only a longitudinal study can settle this issue. One possibility, not entirely heretical,4Loiseau P Do antiepileptic drugs exacerbate seizures?.Epilepsia. 1998; 39: 2-5Crossref PubMed Scopus (19) Google Scholar that cannot be excluded by the data provided is that chronic exposure to antiepileptic drugs may cause hippocampal damage. Did the patients with frequent seizures have a significantly different drug profile from those with “rare” seizures? Longitudinal studies of outcome show that most patients with partial seizures are no less likely to remain intractable than any other group of patients.5Manford M Hart YM Sande JWA Shorvon SD National General Practice Study of Epilepsy (NGPSE): partial seizure patterns in a general population..Neurology. 1992; 42: 1911-1917Crossref PubMed Google Scholar If Salmenperä and colleagues' findings are correct, they may apply only to a select group of patients who tend to accumulate in tertiary referral centres. We believe that their findings are not supported by the methods and results and should not be generally applied to patients with partial seizures. Hippocampal damage caused by seizures in temporal lobe epilepsyAuthor's reply Full-Text PDF