MRI volumetry shows increased anterior thalamic volumes in patients with absence seizures

doi:10.1016/j.yebeh.2006.02.002

Epilepsy & Behavior

Volume 8, Issue 3, May 2006, Pages 575-580

https://doi.org/10.1016/j.yebeh.2006.02.002 Get rights and content

Abstract

The interaction between thalamus and cortex appears to be critical to the pathophysiology of idiopathic generalized epilepsies (IGEs). The objective of this study was to investigate thalamic volumes of a group of patients with IGEs using high-resolution MRI. Thalamic segmentation was performed by the same rater, who was unaware of the diagnosis. Thalamic volumes were divided into anterior half and posterior half. One hundred forty-seven patients were scanned (71 with juvenile myoclonic epilepsy, 49 with generalized tonic–clonic seizures only, and 27 with absence epilepsy). Subgroup analyses with corrections for multiple comparisons showed that, when compared with those of controls, anterior thalamic volumes were increased in patients with absence epilepsy and juvenile myoclonic epilepsy with absence seizures, but not in patients with generalized tonic–clonic seizures only and juvenile myoclonic epilepsy without absence seizures. Our results demonstrated that the anterior thalamus is structurally different in patients with IGEs and absence seizures as compared with patients with IGEs without absence seizures.

Introduction

Magnetic resonance imaging (MRI) is normal in patients with idiopathic generalized epilepsies (IGEs). These age-related epilepsies have a genetic background, and no underlying neuropathological finding is expected [1]. The description of minimal cortical malformations in patients with IGEs raised the possibility of structural abnormalities as a mechanism of seizure generation [2].

According to the initial hypothesis for the pathophysiology of absence seizures and the IGEs, known as the centrencephalic hypothesis, midline subcortical structures are capable of ictal engagement of both cerebral hemispheres [3]. This hypothesis was attractive because it explained the bisymmetrical and bisynchronous onset of the seizures revealed by the EEG findings. Since this description, the thalamus has been a key structure in studies of IGEs.

Experimental data point to involvement of the thalamocortical circuitry in the generation of spike and wave discharges (SWDs) in patients with IGEs [4]. Models of generalized absence seizures suggest that the thalamus is critical to the maintenance of the discharges [4], [5]. Despite this, anatomical investigations in animals did not disclose any relevant structural findings [6].

MRI spectroscopy reveals a thalamic dysfunction in patients with different IGE subsyndromes including juvenile myoclonic epilepsy (JME) and in patients with generalized tonic–clonic seizures [7], [8], [9]. These findings support the presence of a thalamic functional abnormality not only in absence seizures but in all IGE subsyndromes. Previous studies were unable to find any difference in thalamic volumes between patients with IGEs and controls [9], [10], [11].

The real contribution of the thalamus to seizure onset and clinical variability is under investigation, and the pathophysiology of the IGEs is not completely understood. High-resolution MRI allows precise anatomical evaluation in vivo. The objective of this study was to examine the thalamic volumes of a large group of patients with IGE subsyndromes using high-resolution MRI and to compare the findings with those for a healthy control group.

Section snippets

Subjects

MRI was performed in 147 consecutive patients (90 women, mean age = 32 ± 12 (±SD), range = 10–79) and 45 healthy volunteers (22 women, mean age = 32 ± 13, range = 20–60). To investigate thalamic structure in different seizure types (generalized tonic–clonic, absence, and myoclonic), patients were divided into three subsyndromes: 71 had JME (46 women, mean age = 32 ± 9, range = 15–63), 49 had generalized tonic–clonic seizures only (GTCSs, 27 women, mean age = 36 ± 14, range = 14–79), and 27 had absence epilepsy (AE, 17

Clinical features

Most of the patients in the JME (60%, 43/71) and AE (70%, 19/27) groups were taking valproate as the main AED. In the GTCS group, the percentage of patients taking valproate was lower than in the other groups (16%, 8/49), and the most frequently used AED was carbamazepine (41%, 20/49).

Statistical analysis showed that patients in the AE group were younger than patients in the GTCS group (P = 0.01). There was no statistical difference among the other groups in age at MRI evaluation (P > 0.2).

Discussion

This study showed, for the first time, increased thalamic volumes in a large group of patients with IGE. A previous study evaluating the thalamus in 17 patients with IGEs, not specifying the subsyndrome, failed to demonstrate differences when compared with controls [10]. In another study quantifying subcortical volumes, including the thalamus, thalamic volumes of 11 patients with IGEs (5 with JME, 2 with juvenile absence epilepsy, and 4 with GTCSs on awakening) did not differ from those of

Acknowledgments

This study was supported by Coordenação de Aperfeiçoamento de Pessoal de Nı´vel Superior (CAPES) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).

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MRI volumetry shows increased anterior thalamic volumes in patients with absence seizures

Abstract

Introduction

Section snippets

Subjects

Clinical features

Discussion

Acknowledgments

Epilepsy Res

NeuroImage

Neuroscience

Epilepsy Behav

Epilepsy Behav

Neuropathological findings in primary generalized epilepsy: a study of eight cases

Epilepsia

Epilepsy and functional anatomy of the human brain

Generalized epileptic disorders: an update

Epilepsia

Evolving concepts on the pathophysiology of absence seizures: the cortical focus theory

Arch Neurol

Thalamic dysfunction in juvenile myoclonic epilepsy: a proton MRS study

Epilepsia

Magnetic resonance spectroscopy and imaging of the thalamus in idiopathic generalized epilepsy

Brain

MRI volumetry of the thalamus in temporal, extratemporal, and idiopathic generalized epilepsy

Neurology

Subcortical nuclei volumetry in idiopathic generalized epilepsy

Epilepsia