Classification, Investigations and Treatment of Epilepsy:
The classification of epilepsy brings together the seizure semiology and other aspects of the history and investigations. The International League against Epilepsy classified epilepsies as:
- Idiopathic – Thought to be primarily genetic with generalized seizures, sometimes group as more specific syndromes. Account for about 10-20% of cases.
- Symptomatic – Partial onset seizures associated with a structural lesion, such as rumour, cortical dysplasia, infection, head injury or trauma – about 30-40% of cases. The combination of the site of seizure onset and the underlying pathology leads to the diagnosis: for example: post traumatic frontal lobe epilepsy’ or temporal lobe epilepsy due to mesial temporal sclerosis or symptomatic occipital lobe epilepsy secondary to an arteriovenous malformation’.
- Cryptogenic – Partial onset seizures for which no cause has been found. Account for about 50% of patients.
With developments in understanding, particularly in genetics, limitations with this general practical classification have arisen – for example familial frontal onset epilepsy (associated with a mutation in the gene encoding the neuronal nicotinic acetylcholine receptor (nAChR) alpha-4 subunit) is idiopathic yet partial onset epilepsy. Newer proposals und consideration suggest the classification should move to genetic, structural/metabolic’ or unknown cause rather than the groups given above.
Selected Idiopathic Epilepsy Syndromes (by age of onset)
1. Childhood absence epilepsy (common)
- Absence seizures begin between 4 and 12 years of age. Family history in 40% of patients. The absence may occur many times a day with duration of 5-15 seconds.
- Frequent episodes lead to falling off in scholastic performance.
- Attacks rarely present beyond adolescence.
- In 30% of children, adolescence may bring tonic/clonic seizures.
- Distinction of absences from complex partial seizures is straightforward; the latter are longer 30 seconds or more and followed by headache, lethargy, confusion and automatism. EEG finds 3 Hz spike and wave.
2. Juvenile Myoclonic Epilepsy (Common)
Myoclonic jerks begin in teenage years, typically in the morning. Develop tonic/clonic seizures, often with sleep deprivation, in late teens. Occasionally have absence seizures. EEG frequently finds 4-5 polyspike and wave discharges.
EPILEPSY INVESTIGATION
Investigations are directed at:
- Corroborating the diagnosis of epilepsy
- Classifying the type of epilepsy
- Looking for an underlying cause
- Eliminating alternative diagnoses
The relative emphasis of these elements will depend on the clinical situation. For most patients the clinical diagnosis of a seizure is secure and the emphasis is to seek the cause and to classify the epilepsy to direct treatment. In others the main concern is whether the episodes are seizures or an alternative diagnosis.
1. Neuroimaging
All adults and all with focal onset seizures should be scanned. MRI brain imaging is more sensitive than CT and many lesions, for example small turnouts, cortical dysplasia or hippocampal sclerosis will be missed on CT.
2. EEG
- Standard interictal EEG is relatively insensitive – though this varies according to the type of epilepsy (it is very sensitive in childhood absence epilepsy).The interpretation of abnormalities requires caution; 0.5% of the normal population have interictal spikes or sharp waves (epileptic discharges) as compared to 30% of patients after their first seizure.
- The pattern of abnormalities can point towards a focal or generalized onset and can supplement the clinical classification.
- Sleep deprived EEG increases the yield but with the risk of provoking a seizure. EEG shortly after a seizure is more likely to find an abnormality.
- Ambulatory EEG recording increases the chance of finding an abnormality and of recording a clinical event. The gold standard investigation is simultaneous EEG monitoring and video monitoring (video telemetry).
3. Eliminating Alternatives
- ECG should be done in all patients with seizures. This is a simple cheap test and a small number of epilepsy mimics can be identified this way, e.g. prolonged QT syndrome.
- Prolonged ECG may be useful in patients with possible cardiac syncope especially in patients with sleep associated events. Implantable loop recorders can be used when patients have infrequent events.
- Head up tilt table testing is often helpful in the diagnosis of neurocardiogenic syncope.
- Metabolic investigation to consider includes fasting glucose for insulinoma and synacthen test for Addison’s disease.
4. Advanced Investigation
- Volumetric MRI can identify hippocampal sclerosis not apparent on conventional imaging.
- Functional imaging, using ictal and inter-ictal SPECT may be helpful in identifying an epileptogenic focus when evaluating patients for surgery.
- Advanced EEG techniques for example using sphenoidal electrodes or recording from surgically inserted intracranial grid or depth electrodes can help localize a focus before surgery.
EPILEPSY TREATMENT
- Basic principles: Most patients respond to anticonvulsant drug therapy. Drug treatment should be simple, preferably using one anticonvulsant (monotherapy). Polytherapy should be avoided to minimize adverse effects and drug interactions.
- Treatment aims to prevent seizures without side effects though this is not always achieved.
- Surgery is an option in a small number on non-responders.
- Teratogenicity: It is important to consider the teratogenetic risks when starting any anticonvulsant in a woman of childbearing age. Large prospective studies have established rates of major congenital malformations for widely used drugs: those on no medication, carbamazepine or lamotrigine had similar rates of around 3%; in valproate monotherapy the rate was significantly higher at 6%; polytherapy overall was about 6%, and 9% if valproate was one of the drugs.
- Interactions: Many anticonvulsants (especially carbamazepine, phenytoin, phenobarbitone) induce liver enzymes to increase metabolism of other drugs (notably the oral contraceptive, warfarin and other anticonvulsants); valproate inhibits liver enzymes.
- Blood levels: Monitoring levels is useful for phenytoin because of the difficult pharmacokinetics. Other blood levels can occasionally be useful to check the patient is taking the medication or for toxicity.
1. Drug choice:
- Idiopathic Generalized Epilepsy: sodium valproate; lamotrigine; topiramate; levetiracetam; phenytoin.
- Partial (Focal) Epilepsy: lamotrigine; carbamazepine; sodium valproate; Phenytoin; Phenobarbitone; Levetiracetam;Topiramate;Tiagabine; Zonisamide; Oxcarbazepine; Gabapentin; pregabalin; lacosamide.
- Those drugs asterisked are typically used for monotherapy others as add-on therapy when control sub-optimal. The choice of anticonvulsant will be a balance between efficacy, adverse efficacy, teratogenicity and drug interactions and the patient should be involved in this decision.
2. Lifestyle Issues: Generally there should be as few restrictions as possible. Patient should be made aware of potential triggers to avoid – sleep deprivation, excess alcohol, and, where relevant flashing lights (though most patients are not photosensitive). Sensible precautions – showering rather.
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