Pediatric Epilepsy: Medical Intractability
Medical management with AEDs remains the treatment of choice for epilepsy in adults and children. Medically intractable epilepsy has been defined as persistent seizure activity, which, despite maximal medical treatment, remains sufficiently debilitating to warrant the risks of surgery. This definition has different meanings in the pediatric and adult epilepsy populations.
Adults often have a low frequency of seizures, and it is not uncommon for adults to be termed "intractable," while experiencing only one seizure a month. As a result, the evaluation process in these patients is often a long process of medication adjustments, different medications in mono- and polytherapy, and compliance checks before surgical evaluation is initiated.
(See also Adult Epilepsy Program)
In contrast, certain pediatric seizure syndromes are uniquely defined by their seizure intractability, (e.g.) congenital malformations such as hemimeganencephaly, Sturge-Weber syndrome, or Rasmussen’s encephalitis, where 40-100 seizures a day are not an unusual occurrence despite maximal medical therapy. Medical regimens in these instances, often fail with poor responses to first- and second-line medications, as well as to polytherapy.
Because of the high frequency of seizures, trials of medical management can be attempted and discarded in short periods of time. It is generally accepted that the initial evaluation in children with intractable seizures can be performed expeditiously, particularly with the catastrophic epilepsy syndromes, with early recommendations for surgical evaluation and intervention in children as young as medically and surgically practical.
Many factors may predispose children to the development of seizures and epilepsy, including: genetic and congenital malformations, intrauterine and postnatal insults, anoxic injuries, infections (viral and bacterial), vascular malformations and compromise (e.g.) ischemia, trauma, and tumors. A significant percentage of cases of epilepsy in children though remains idiopathic, although this has continued to become less due to advances in neuroimaging.
The range of epilepsy syndromes and surgical considerations for treatment is dependent on the underlying pathology and pathophysiology, and is categorized similarly in children and adults. Obviously, the type of pathology defines the planning as to the type and extent of the surgical approach. This is well-illustrated in patients with complex partial seizures of temporal lobe origin where the predominant pathology is medial temporal sclerosis, (MTS).
Previously, in all cases, following the initial evaluation, all the patients underwent invasive monitoring with depth electrodes (DE). More recently, this pathologic process has become more easily imaged anatomically with magnetic resonance imaging (MRI) and MR volumetrics, and functionally with positron emission tomography (PET) and single photon emission tomography (SPECT) scanning. Because this entity is a single, small, epileptic focus, relatively easily diagnosable, readily accessible and resectable with a temporal lobectomy, and with good outcomes (high seizure-free rate with low morbidity), now based on the imaging, the approach to these patients has now for the most part progressed beyond invasive monitoring. In contrast, in children with lateral temporal processes, invasive monitoring may be necessary to define the extent of the epileptogenic zone.
While MTS is a common primary pathology in children, childhood seizures frequently are secondary to a lesion or neocortical abnormality. Lesional types of epilepsy usually include low-grade gliomas, hamartomas, and/or vascular malformations though other etiologies are common. An underlying low-grade neoplasm in the pediatric population presents as new-onset seizures in 15-60% of epilepsy cases, and likewise is often amenable to surgical resection. Similarly, seizures are the most common presentation of pediatric vascular malformations, which contrasts with adults who most often present with hemorrhage. As a result, it is imperative that in an otherwise healthy child with new-onset, recurrent seizures an imaging study should always be obtained to determine if the event(s) is secondary to an underlying lesion.
Epileptic foci secondary to lateral neocortical and extratemporal anomalies in children are frequently due to architectural abnormalities, such as cortical dysplasia, migrational defects, and other congenital developmental abnormalities. While present day anatomic and functional imaging frequently can often identify these anomalies, there is still a limit to their resolution. As a result, many of these patients require chronic invasive monitoring to further define the seizure focus, particularly the relationship to normal, eloquent areas of cortex. In the future, further improvements in neuroimaging may replace the need for invasive evaluation in this group of patients.