Imagine sitting in the waiting room of a pediatric epilepsy clinic and observing the variety of patients awaiting their turn to be evaluated. A 6-year-old child, initially referred for "staring spells," is now here for a follow-up appointment with well-controlled childhood absence epilepsy. In a wheelchair you see a 13-year-old child with spastic quadriparetic cerebral palsy, moderate mental retardation, and poorly controlled symptomatic localization-related epilepsy. She is here to have the settings on her vagus nerve stimulator adjusted in the hope that her secondarily generalized seizures might become less frequent An 8-month-old infant has been worked into the schedule, with continued clusters of infantile spasms despite completing a trial of adrenocorticotropic hormone (ACTH) . A new patient is here for a second opinion about whether or not his brief stereotyped events of generalized shaking with partial loss of consciousness are epileptic in nature Finally, there is an 8-year-old for a 6-month postoperative follow-up visit after a focal neocortical resection to remove an area of cortical dysplasia, who happily remains seizure free As different as these patients may be in age, clinical phenomenology, and response to therapy, they all have epilepsy Clearly, this is a heterogeneous collection of distinct disorders, which may more appropriately be referred to as "the epilepsies ." To understand this clinical spectrum, one must be familiar with both what unifies these conditions and what makes each distinct .
The definition of epilepsy is deceptively simple: having two or more unprovoked seizures separated by more than 24 hours . Each component of that definition is important to bear in mind. Seizures are paroxysms of abnormally hyperexcitable and hypersynchronous cortical activity that result in a change in sensation, motor function, behavior, or the sensorium . If the seizure occurs immediately following a precipitating event, then it is referred to as an acutely provoked/reactive seizure or acute symptomatic seizure As mentioned previously, a common example of such an event would be a febrile seizure: 2 to 4% of all children between the ages of 6 months and 5 years experience a generalized seizure lasting less than 15 minutes in association with a fever not caused by a central nervous system (CNS) infection . In this case, the acute provoking event—the fever—is immediately followed by the seizure . Other examples of acute symptomatic seizures would include those that occur at the time of trauma, in the context of hyponatremia, or in association with a withdrawal syndrome (e g , alcohol) In contrast, with epilepsy, there is no immediate provoking event for the seizure . At times, the seizure may arise from an old injury such as from a prior stroke Because the precipitating event precedes the seizure by weeks to years, such an event is considered unprovoked and is often referred to as a "remote symptomatic seizure." Finally, in order to meet the definition of epilepsy, two or more unprovoked seizures must be separated by more than 24 hours The reason for this is that rapidly recurrent seizures occurring close together carry the same epide-miological risk of eventual recurrence as a single seizure 12
If a patient has two or more unprovoked seizures, then that patient may justifiably be labeled as having epilepsy. Given the broad nature of this definition, many different types of clinical phenotypes fall under the cover of this one large umbrella It is a bit like stating that one lives in North America—helpful information but not very specific! Nowhere is this more evident than in the pediatric epilepsies in which cause, clinical phenomenology, and outcome vary greatly As with the epilepsies that arise in adulthood, children may suffer seizures as a consequence of trauma, CNS infections, strokes, and other brain insults A particular example of this would be children who suffer injuries in utero or during the process of birth . Largely unique to childhood are seizures that arise from developmental brain malformations such as disorders of neuronal migration leading to focal cortical dysplasias It is interesting to note, however, that although the abnormally formed cortex is present from birth, an epileptic disorder may not develop for many years The reasons for this remain unclear
To bring some semblance of order to this landscape, the epilepsies have historically been categorized or classified on the basis of electroclinical features Clinically, this is accomplished using a schema developed by the International League Against Epilepsy (ILAE), which utilizes etiology and seizure type 4,6 If the patient's epilepsy arises from an evident cause, such as a remote symptomatic seizure due to an old brain injury, then the epilepsy is referred to as symptomatic (Figure 1 1) In general, the abnormal area of the brain will be evident on MRI or other imaging modality Another example of a symptomatic epilepsy would be one arising from a focal cortical dysplasia . However, some epilepsies are caused not by a clear anatomic abnormality but are instead inherited—either as a single mutation or, more
FIGURE 1.1 MRI images and EEG data from a teenager with symptomatic localization-related epilepsy. This 15-year-old right-handed boy had left-sided hemiplegic cerebral palsy and startle-induced complex partial seizures . Panels A and B are representative Tl-weighted postcontrast MRI images (coronal and axial planes, respectively) demonstrating the damage caused by an in utero right middle cerebral artery territory infarction (the left side of the image corresponds to the right side of the brain). Panel C shows the patient's EEG immediately prior to and following an auditory startle as well as several seconds into his typical electrographic ictal discharge Note the high-amplitude slow activity with superimposed faster frequencies in the leads labeled Fp2-F4, F4-C4, and C4-P4, indicating that the seizure is arising from the right frontocentral region (by convention, EEG leads with even numbers are on the right, and those with odd numbers are on the left; Fp = Frontal polar, F = frontal, C = central, and P = parietal) . The patient underwent definitive surgical resection and remains seizure free off medication after more than 4 years
FIGURE 1.1 MRI images and EEG data from a teenager with symptomatic localization-related epilepsy. This 15-year-old right-handed boy had left-sided hemiplegic cerebral palsy and startle-induced complex partial seizures . Panels A and B are representative Tl-weighted postcontrast MRI images (coronal and axial planes, respectively) demonstrating the damage caused by an in utero right middle cerebral artery territory infarction (the left side of the image corresponds to the right side of the brain). Panel C shows the patient's EEG immediately prior to and following an auditory startle as well as several seconds into his typical electrographic ictal discharge Note the high-amplitude slow activity with superimposed faster frequencies in the leads labeled Fp2-F4, F4-C4, and C4-P4, indicating that the seizure is arising from the right frontocentral region (by convention, EEG leads with even numbers are on the right, and those with odd numbers are on the left; Fp = Frontal polar, F = frontal, C = central, and P = parietal) . The patient underwent definitive surgical resection and remains seizure free off medication after more than 4 years commonly, as a collection of interacting mutations Epileptologists refer to such epilepsies as idiopathic . Several common epilepsies of childhood, such as childhood absence epilepsy and benign Rolandic epilepsy, are considered idiopathic Finally, some epilepsies occur in patients without an evident cause: the MRI is normal, there is no clear heritability, and no aspect of the workup reveals a potential etiology. These epilepsies are labeled cryptogenic—literally meaning that the cause is hidden . One of the primary goals of the epilepsy research community is to abolish the need for this category by increasing our understanding of what causes epilepsy as well as expanding our repertoire of tools available for diagnosis
In addition to etiology, the present classification scheme utilizes seizure type as a criterion Seizures that arise from a particular region of the brain are labeled partial, whereas seizures that involve both hemispheres from onset are referred to as generalized. Rather than using the term "partial" when categorizing the epilepsies, the ILAE scheme has adopted the term localization related. It should be noted
FIGURE 1.1 (continued)
that seizures may begin focally (as a partial seizure) and then spread to involve the other hemisphere . Such a seizure is said to be secondarily generalized. Although not utilized in the classification scheme, partial seizures are further divided into simple partial seizures if they do not affect consciousness, and complex partial seizures if consciousness is in any manner impaired . Putting the etiologic and phenomenologi-cal criteria together yields the appropriate classification . For example, epilepsies may be symptomatic localization related (a clear anatomic cause affecting just one part of the brain), idiopathic generalized (an inherited epilepsy producing seizures that affect both hemispheres at the outset, such as childhood absence epilepsy), cryptogenic localization related (epilepsy with no clear etiology, which arises from a restricted focus), or any other combination of terms . As will become clear in the chapters to follow, utilizing this scheme is helpful in determining an appropriate evaluation and management strategy
Another peculiarity of pediatric epilepsy is the concept of an epilepsy syndrome: a constellation of a particular type of seizure (or seizures), EEG features, and other clinical phenomenon often associated with a particular age of onset For example, West syndrome represents the combination of infantile spasms (a particular type of seizure), an interictal EEG pattern called hypsarrhythmia, and developmental arrest or regression with a peak age of onset between 3 and 7 months of age . 15 Although still clinically diverse, epilepsy syndromes seem to represent a more homogeneous clinical population than is afforded by the ILAE classification scheme . For example, childhood absence and juvenile myoclonic epilepsy are both categorized as idio-pathic generalized epilepsies, but they differ significantly in their age of onset, predominant seizure type, and rate of remission
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