Cellular Basis of Epilepsy Flashcards
What are the epilepsies characterised by?
Recurrent unprovoked epileptic seizures
What is an epileptic seizure?
A transient occurrence of clinical signs and/or symptoms due to excessive and hyper-synchronous activity of populations of neurons in the brain.
What do the clinical manifestations of epileptic seizures depend on?
The regions of the brain involved – at onset and from secondary spread.
What is epilepsy?
A group of neurological diseases with enduring alterations in the brain resulting in abnormally increased predisposition to seizures.
What are the 3 different classes of epilepsy?
- Genetic (idiopathic/primary)
- Structural/metabolic (symptomatic/secondary)
- Unknown (cryptogenic)
How are seizures classified?
Based on clinical features and EEG findings
How are epilepsies and epileptic syndromes classified?
Epileptic disorders with similar signs, symptoms, prognosis and response to treatment.
Important for choosing treatment options and counselling patients regarding aetiology, genetics and likely prognosis etc.
What are the 3 ILEA classifications of seizures?
Partial (Focal) Seizures: arise in a limited number of cortical neurones within one hemisphere.
Generalised Seizures: appear to arise simultaneously in both hemispheres.
Unclassifiable Seizures
What are partial (focal) seizures?
Seizures that arise in a limited number of cortical neurones within one hemisphere.
What are generalised seizures?
Seizures that appear to arise simultaneously in both hemispheres
What are the 3 different classifications of the epilepsies/epileptic syndromes?
Genetic (idiopathic)
Structural/metabolic (symptomatic)
Unknown
What is genetic (idiopathic) epilepsy?
Underlying brain is structurally and functionally normal.
Onset during childhood/teenage and may remit.
Respond well to medication.
Likely have a genetic basis - ion channels.
Most common in childhood/teenage years
What is structural/metabolic (symptomatic) epilepsy?
Seizures result from some identifiable structural/functional brain abnormality.
Uncommonly remit, and often incompletely controlled with medication.
What are the current concepts for the causes of epilepsy?
Disturbance in the balance between inhibition and excitation of cortical neurones and neuronal networks.
Either increases or decreases in neuronal inhibition or excitation.
Result in neuronal networks that fire in an uncontrolled, hyper-synchronous, self sustained manner. May result from a wide variety of causes:
Genetic, congenital/developmental, traumatic, infectious, metabolic, drugs etc.
What are the neurobiological and cellular mechanisms required to generate epileptic neuronal networks?
- Alterations in neuronal network components
- Loss of inhibitory neurons (inhibitory neurons of hippocampus are particularly sensitive)
- Gain of excitatory neurons (neurogenesis)
- Aberrant sprouting
- Alterations in intrinsic neuronal cellular excitability
- Alterations synaptic transmission
- Alterations in the extra-neuronal environment
What role does the hippocampus play in mesial temporal lobe epilepsy?
Histolopathology in humans and animal models with mesial temporal lobe epilepsy shows a characteristic pattern: mesial temporal sclerosis (MTS)
What is the histopathology of mesial temporal sclerosis?
Cell loss in CA1, CA3 and dentate hilus regions: extrahippocampal, e.g. pyriform, entorhinal cortex, subiculum
Mossy fibre sprouting
Gliosis
What is the relationship between epileptogenesis and disease progression?
Seizures beget seizures
Seizures accelerate the remodelling, making seizures more likely to occur
What is the relationship between age and epilepsy incidence?
New onset epilepsy is common at all ages: bimodal peak in young and old
What are the causes of idiopathic generalised epilepsy?
Believed to be genetically determined
5-10% Mendelian monogenic inheritance patterns
What do most patients with IGE have?
Complex inheritance patterns
What is the most important imaging modality in epilepsy evaluation?
MRI
How are pathological substrates in patients with focal epilepsy identified?
Using MRI
What is the most common pathology in adults with partial epilepsy?
Mesial temporal sclerosis
What are the MRI features in mesial temporal sclerosis?
Hippocampal atrophy
Increased T2 signal
Decreased T1 signal
Loss of internal architecture
What is focal cortical dysplasia?
Focal regions of disturbed cortical development and architecture
What can be seen on MRI in focal cortical dysplasia?
Focal thickening of the cerebral cortex.
Blurring of the grey/white interface.
Gyral abnormalities e.g. polymicrogyria, macrogyria.
May be associated with a region of increased T2 signal.
What is periventricular nodular heterotopia?
A generalised malformation due to abnormal neuronal migration.
Nodular masses of grey matter diffusely lining the ventricular walls.
Bilateral or focal
Cortex and neurological function usually normal.
Can be inherited (bilateral) - X-linked dominant form (FLNA gene); Autosomal recessive form (ARFGEF2)
What do approx. 15% of patients with partial epilepsy have?
Low grade tumours - Most common cause of new onset partial seizures 35-55 yrs.
What are the 3 different types of low grade epileptogenic tumour?
Gliomas (most common - 72-88%)
Meningiomas
Dysembryoplastic Neuroepithelial Tumors (DNET)
What affects the epileptogenicity of a tumor?
Site
Centro-tempro-parietal region most epileptogenic.
Cortical>subcortical
What role do vascular lesions play in epilepsy?
Approx. 10% of patients with chronic drug-resistant partial epilepsy have vascular lesions.
Includes cavernomas and arteriovenous malformations
Note: Venous angiomas & capillary telangiectasias not established to be epileptogenic.
What is a cavernoma?
A tangled mass of tightly arranged abnormal vessels made of common hypocellular walls.
Vary from few mm to several cm.
Seizures common (40-70%), hemorrhage rare.
Usually single, but can be multiple in familial cases.
What are the MRI features of a cavernoma?
Well demarcated lesion with characteristic “target” appearance of high T2 signal core with low signal halo.
What are arteriovenous malformations?
Congenital vascular abnormalities consisting of communicating arteries and veins without intervening capillary beds.
Seizures 2nd most common presentation (17-40%).
Especially <20 yrs, > 3 cm, and temporocentral site.
What are the MRI features of arteriovenous malformations?
Less well demarcated lesions consisting of serpentine signal voids interspersed with regions of heterogeneous signal.
What is focal encephalomalacia?
Focal lesion resulting from previous destructive insult, esp. trauma, stroke, infection.
What are the MRI features of focal encephalomalacia?
Irregular area of atrophy of the cerebral cortex and underlying W.M.
Surrounding region of increased T2 signal (gliosis)
May be associated with a large cystic region
What do anti-epileptic drugs do?
Decrease the frequency and/or severity of seizures in people with epilepsy
Treats the symptoms (seizures), not the underlying epileptic condition
Need to be taken for years, often lifetime.
What are the 3 non-medical treatments for epilepsy?
Surgery
Neurostimulators
Dietary
When is epilepsy surgery performed?
When there’s continuing seizures despite adequate trials of several appropriate AEDs.
Seizure interfere with quality of life.
A surgically remediable epilepsy syndrome.
Focal epilepsy where the origin of the seizures can be localised to a brain region that can be resected an acceptably low risk of inducing a significant
Goal is to improve quality of life by controlling seizures (seizure free) and reducing medication burden
What are the current treatment gaps for epilepsy?
Medically refractory seizures are common
Poor medication tolerability
No anti-epileptogenic or disease modifying treatments
No treatments for co-morbidities (psychiatric and neurocognitive)
