Classification of Epilepsy Syndromes

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Similar to the approach to any other neurologic disorder, it is important for the clinician to arrive at a syndromic, topographic, and etiologic diagnosis in each patient with epilepsy. There are many different epileptic syndromes, which are distinguished on the basis of 1) type or types of epileptic

CASE STUDY

Presentation: For more than a year, a couple living in a poor country had been facing a significant socioeconomic dilemma related to the costs of treatment of their 11-year-old son, who had recurrent episodes of disconnection from the environment. The episodes began 2 years earlier, and after sequential trials of phenobarbital, phenytoin, and carbamazepine, the boy was given newer and more costly antiepileptic drugs. These medications have also fallen short of controlling the attacks, but the boy was maintained on oxcarbazepine 1,500 mg/day. Since the beginning of his problem, school performance and behavior have worsened. Despite the impact of the costs on the household budget, the parents have complied with all physicians' prescriptions.

Seizures were initially noted at school and described as episodes lasting about 10 seconds, characterized by sudden arrest of activity, staring, and drooling. There was questionable confusion for a few seconds afterwards, although the boy could easily resume his activities. Two to four of these episodes occurred every day. About 1 year after the onset of seizures, he had a single nocturnal generalized tonic-clonic seizure. Previous medical history was remarkable for three brief febrile convulsions between ages 1 and 3 years, and there was also a positive family history for febrile convulsions and epilepsy.

Evaluation: General medical and neurologic examinations were normal. Two EEGs during wakefulness and sleep showed normal background activity and sharp waves over the centrotemporal regions, which increased markedly during sleep. Photic stimulation was not available at the EEG lab, and the boy did not cooperate with voluntary hyperventilation. A CT scan was normal, and the parents were informed that an MRI was needed—despite the fact that they would need to pay for the exam. The latter was also normal.

Treatment: Oxcarbamazepine was slowly discontinued, and ethosuximide begun, up to a dosage of 750 mg/day. Outcome: Seizures were completely controlled, although interictal centrotemporal sharp waves persisted on the EEG. Comment: This boy had a form of idiopathic generalized epilepsy, most likely juvenile absence epilepsy. A combination of facts led to misdiagnosis of both the epileptic seizures and the epileptic syndrome, and therefore, to inadequate seizure control and increased costs of evaluation and treatment. A core aspect was the misinterpretation of absence seizures as complex partial seizures. The history of febrile convulsions and the focal epileptiform activity on EEG probably added to the diagnostic confusion. However, both a personal and family history of febrile convulsions and centrotemporal (rolandic) sharp waves are also observed in patients with idiopathic generalized epilepsy syndromes. Furthermore, generalized spike and wave complexes on the EEG may be missed in juvenile absence epilepsy, especially if photic stimulation is not available (a common situation in EEG labs in developing countries) and voluntary hyperventilation is not adequately performed. The very favorable response to ethosuximide—an inexpensive AED specific for absence and myoclonic seizures—supports the hypothesis of an idiopathic generalized epilepsy syndrome.

CASE STUDY

Presentation: This 62-year-old noninsulin-dependent diabetic man experienced generalized tonic-clonic seizures exclusively during sleep 3 years before presentation. His wife did not report focal components, describing instead generalized body stiffening preceded by a loud scream from the very onset of the attacks. Despite treatment with 2,250 mg/day of valproic acid, seizures recurred every month. There were no other vascular risk factors. Family history was positive for stroke, but negative for epilepsy.

Evaluation: General medical and neurologic examinations showed only reduced pinprick and tactile sensation in both feet. Fasting glucose, creatinine, and LDL cholesterol levels were mildly elevated, but other laboratory tests were normal. Two EEGs during wakefulness and sleep were normal. Neuroimaging exams were not available in the patient's region.

Treatment: Phenytoin was started and titrated up to 350 mg/day. Valproic acid was slowly discontinued.

Outcome: Seizures have not recurred for 2 years.

Comment: In the context of generalized seizures occurring only during sleep, normal EEGs, and unavailable neuroimaging facilities, the diagnosis of the type of epileptic seizure and syndrome may be difficult. The clinical key to the present case was that "de novo" idiopathic generalized epilepsy with tonic-clonic seizures is not common at this patient's age. Thus, in the event of inadequate seizure control with an antiepileptic medication best suited to control primarily generalized seizures, the possibility of secondarily generalized seizures without obvious focal features should be considered. With no additional cost, this hypothesis can be tested by introducing or substituting an AED with a greater specificity for partial onset seizures.

seizures; 2) age of seizure onset; 3) etiology; 4) degree of associated neurologic and intellectual deficits; 5) clinical evolution of the epilepsy and any underlying condition; 6) pattern of EEG abnormality; and 7) abnormalities on imaging exams. Identifying an epileptic syndrome implies a particular therapeutic approach and prognosis; however, many patients have epileptic conditions that do not fit into a recognized syndromatic category.

The currently accepted ILAE classification of epilepsies and epilepsy syndromes (Table 2.3) divides these conditions into generalized and localization-related. The former are due to diffuse bilateral disturbances, whereas the latter are due to abnormalities related to a part of one hemisphere. In addition, syndromes are divided into idiopathic, which are benign, age-related genetic disturbances manifesting only as epilepsy; symptomatic, which are secondary to lesions of the brain, either acquired or genetic; and cryptogenic, meaning probably symptomatic, but the etiology is unknown. The prognosis of symptomatic epilepsies depends on the prognosis of the underlying substrate.

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