Epilepsy is amongst the most common neurological conditions in league with Migraine, Stroke and Alzheimer disease. In 1870, Hughlings Jackson an eminent British Neurologist postulated that Seizures were due to ‘an excessive and disorderly discharge of cerebral nervous tissue on muscles.’ This description holds true till date and summarizes the pathophysiology and symptomology of seizure disorders.
The various terms frequently referred to in this field include:
- Seizure refers to a single event
- Epilepsy refers to recurrent seizures, and
- Convulsion defines only its motor manifestation like jerky movement of limbs or facial twitching
The importance of epilepsy lies in its worldwide prevalence and dramatic presentation which instigates a lot of curiosity, misbelieves and social stigmas related to the disease and its treatment.
Epilepsy afflicts 50 million people worldwide out of which 80% reside in low or middle income countries. Most of the epilepsies are curable or can be controlled symptomatically with affordable medications but still are not treated adequately especially in the underdeveloped world due to stigma associated with it like being possessed by an evil spirit.
Epilepsy is a chronic non communicable disease defying age barriers and can affect any age group though causes in each group may vary. It is important to clarify a common myth of communicability in Epilepsy i.e., spread from one person to another. Epilepsy is non communicable. It does not spread from one person to another.
Among first-degree relatives of all epileptics, the cumulative incidence of epilepsy to age 40 was 5%, and risk was increased 3-fold, compared with incidence rates in the general population. The pace of gene discovery in the epilepsies is increasing rapidly, but for most affected individuals the genetic contributions are complex and the specific genes that influence the risk of developing seizure disorder remain to be identified.
A single seizure is not an uncommon occurrence and may happen in a number of medical conditions. It may never happen again and does not justify the label of Epilepsy which by definition is a recurring event.
First attempts to classify Epilepsies date back to the time of Galen (2nd century AD). The International League Against Epilepsy (ILAE) is credited with the development of the first proposal of an epilepsy classification in 1969.
The 1969 ILAE classification system established a major dichotomy between Generalized and Focal epilepsies, based on clinical characteristics of each seizure type in conjunction with Electroencephalographic (EEG) features, Etiology, and Age at manifestation.
The International League Against Epilepsy (ILAE) Commission on Classification and Terminology revised the concepts, terminology, and approaches for classifying seizures and forms of epilepsy.
Generalized seizures were redefined as occurring in and rapidly engaging bilaterally distributed networks whereas Focal seizures were redefined as occurring within networks limited to one hemisphere and either discretely localized or more widely distributed. The concepts of Generalized and Focal do not apply to electroclinical syndromes. Genetic, Structural-metabolic, and Unknown represent modified concepts to replace Idiopathic, Symptomatic, and Cryptogenic.
Classification of Generalized seizures was simplified. Generalized epilepsies can present in following types:
- Tonic Seizures: i.e., Stiffening of the entire body
- Clonic Seizures: Continuous jerking
- Tonic–Clonic Seizure
- Myoclonic Seizures: Brief electric shock like reaction
- Atonic Seizures: Loss of tone of the body
- Absence Seizures
All types except Absence present with positive phenomenon.
No natural classification for focal seizures exists. Focal epilepsies are further divided into one without loss of consciousness and other with loss of consciousness.
Focal seizures should be described according to their manifestations (e.g., dyscognitive, focal motor). They can present with various symptomology like simple motor march of numbness /weakness from fingers upwards in upper limb, head or eye turning to one side, speech arrest or verbalization or vocalization, dystonic posturing of limbs, formed or unformed hallucination ,vertiginous or gustatory or olfactory sensation or déjà vu or jamais vu sensation etc. The symptoms basically represent the functions of the part of brain from where seizure is arising.
The first revision in 1985 led to the ‘Syndromic’ approach to epilepsy classification with a listing of multiple epileptic syndromes defined by Seizure type(s), Etiologies, Age at onset, or Seizure frequency, or a combination of two or more of these features. This classification provides a universal terminology facilitating communication among clinicians and is in wide use. However, less than one in five of epileptic patients can be assigned to one of the listed specific epilepsy syndromes. It gives a false impression of diagnostic precision in what are essentially uncertain cases and provide only part of the information required for the clinical management of a patient.
The Cleveland Clinic Foundation developed a five-dimensional patient-oriented epilepsy classification which assesses:
- Location and extent of the epileptogenic zone
- Semiologic seizure types
- Seizure frequency, and
- Related medical conditions
Epilepsy can be idiopathic [ie no known underlying cause] or symptomatic or secondary. The most common secondary causes are:
- Head trauma
- CNS infection
- Brain injury due to prenatal, peri- or post natal insult.
- Genetic syndromes/Developmental abnormalities
- Brain tumor
- Electrolyte imbalance
- Few medicines/Alcohol
Surgery maybe the only recourse in certain epileptogenic entities that include:
- Rasmussen encephalitis: a rare, progressive, unihemispheric neurological disorder of previously normal children who develop intractable focal seizures, epilepsia partialis continua, and—as the disorder progresses—hemiparesis and progressive cognitive decline.
- Hypothalamic hamartoma: associated with Gelastic epilepsy characterized by episodes of pathological laughter warrant timely treatment as they are known to progress into more serious forms of partial and generalized seizure disorders. Left untreated, these often progress to encephalopathy, associated with cognitive and psychological implications.
- Hemiconvulsive hemiplegic syndrome involves initial sudden and prolonged unilateral convulsive seizures, followed by transient or permanent hemiplegia and epilepsy during infancy or early childhood. Seizures are prolonged, difficult to control.
However the majority of epilepsy patients considered for Surgery are cases of Intractable epilepsy or Drug-resistant epilepsy.
Drug-resistant epilepsy is defined as a failure of two or more appropriately selected and adequately tried anticonvulsant medications to achieve seizure freedom for a sustained period of time. This may occur in either monotherapy or polytherapy. Once this definition has been met, the likelihood that further medication trials will lead to seizure freedom is in the range of 5% to 10%.
The reasons for an incorrect label of Drug-resistant epilepsy include:
- Wrong diagnosis
- Wrong drug
- Wrong dose, or
- Poor compliance
Patients with epilepsy who are drug-resistant should be referred to an Epilepsy center for a surgical evaluation or more specialized care. The odds of being seizure free following Epilepsy surgery versus continued medications are around 4 to 3. Currently, surgical referrals occur late in the disease.
Intractable epilepsy or Drug-resistant epilepsy (DRE) should be anticipated early at the onset of epilepsy in the following situations:
- Inadequate seizure control with an appropriate first AED predicts a high probability of development of DRE
- Inadequate seizure control with two appropriate and adequate AEDs is unlikely to achieve seizure freedom with a third drug, the chance being less than 10%
- High AED doses do not increase rates of seizure control. They are likely to increase adverse reactions and undesirable side-effects
- Newer AEDs do not significantly change the above-mentioned equations, and probably only increase the cost burden
- Failure of response to AEDs should be considered when two AEDs tried individually or in combination have failed to control seizures particularly when appropriate AEDs have been used in adequate therapeutic doses for an adequate period of time
Epilepsy is known since 4000 BC and since then till date the field has advanced in leaps and bounds. The most important advance in the management of Epilepsy is the Surgical correction of intractable epilepsy which could in selected cases give the patient a seizure and drug free lifestyle.
Investigations for Surgical treatment of epilepsy are unique because they help us localize the focus of epilepsy and include:
EEG using scalp electrodes
EEG reveals a epileptic focus
MRI Brain confirms left mesial sclerosis; a lesion closely associated with temporal lobe epilepsy!
Magnetoencephalography is performed in tertiary centers for better delineation of epileptic foci as shown below.
Positron Emission Tomography reveals lowered metabolism in the foci.
Epilepsy surgery is a procedure that either ‘removes’, ‘isolates’, ‘irradiate’ or ‘stimulate’ the area of your brain where your ‘seizures’ originate.
A team approach is a must for Epilepsy surgery and its goal in an individual case must be defined. The team comprises of a Neurologist, Neuroradiologist, Electrphysiology studies technician, Psychologist and Neurosurgeon. Repeated counseling of patient and family members regarding expectations from surgery must be clarified and documented.
Benefits of Surgery in Epilepsy vary from helping reduce falls from seizure, decreased number of epileptic attack, halt progressive neurological deficit and in few cases may make patient seizure and drug free for life.
Surgical results are very encouraging in Temporal lobe epilepsy. The planning and operative picture is shown above.