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CHAPTER 410  THE EPILEPSIES    2283 hemisphere, produce signs and symptoms corresponding to the specific region of the brain that is affected by the seizure. Generalized seizures rapidly affect extensive neuronal networks on both cerebral hemispheres, and their signs and symptoms are consistent with substantial involvement of both sides of the brain. Seizures are not synonymous with epilepsy. The epilepsies should be distinguished from situations in which acute brain insults (e.g., infections,
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  CHAPTER   410 THE EPILEPSIES 2283 hemisphere, produce signs and symptoms corresponding to the specicregion o the brain that is afected by the seizure. Generalized seizures rapidly afect extensive neuronal networks on both cerebral hemispheres, and theirsigns and symptoms are consistent with substantial involvement o both sideso the brain.Seizures are not synonymous with epilepsy. Te epilepsies should be dis-tinguished rom situations in which acute brain insults (e.g., inections,trauma, intoxication, metabolic disturbances) cause one or more seizures without a resulting chronic seizure tendency.  Acute symptomatic seizures, or  provoked seizures  , constitute about 40% o all incident cases o nonebrileseizures, typically respond to treatment o the provoking actor, and do notrequire long-term treatment with antiepileptic drugs.Te epilepsies are a group o conditions in which an underlying neurologicdisorder results in a chronic tendency to have recurrent, unprovoked sei-zures. Under these circumstances, the occurrence of two or more seizures estab-lishes the diagnosis of epilepsy. Te causes, types, and clinical expression o the epilepsies are numerous and varied. However, some o the epilepsiesconorm into identiable epileptic syndromes  , which consist o clusters o clinical and electroencephalographic (EEG) eatures that have speciccauses, respond to particular treatments, and may have specic prognosticimplications. EPIDEMIOLOGY  Incidence and Prevalence Seizures are common in the general population, and about 1 in 10 people willexperience a seizure in their lietime. Most o these seizures are provoked by acute events and are not related to epilepsy. Te overall annual incidence o acute symptomatic seizures, excluding ebrile seizures, in developed coun-tries is about 39 per 100,000 people. Te incidence is higher in men andollows a bimodal age distribution. Incidence is at its highest peak in the rst year o lie (up to 300 per 100,000), reaches a nadir o 15 per 100,000 in thethird and ourth decades o lie, and rises again to 123 per 100,000 aer 75 years o age. Tese diferences are aributable to the high incidence o acutesymptomatic seizures associated with metabolic, inectious, and encephalo-pathic causes during the neonatal period, and o cerebrovascular and degen-erative diseases in elderly people.Te epilepsies are common and afect humans o any age. Aer headache,the epilepsies are the most requent chronic neurologic condition seen ingeneral practice worldwide. In developed countries, the prevalence o activeepilepsy ranges rom 5 to 7 per 1000 people, and the annual incidence rangesrom 35 to 52 per 100,000, varying by age. Te incidence o epilepsy peaksin children younger than 5 years at 60 to 70 per 100,000, decreases through-out adolescence to 30 per 100,000 in early adulthood, and rises again aerthe sixth decade, reaching a peak o 150 to 200 per 100,000 people older than75 years. Overall, the incidence and prevalence o the epilepsies are higher indeveloping countries, largely owing to a higher requency o perinatal insults,trauma, and inectious disorders o the brain and to suboptimal treatment. Inthese countries, the median prevalence o active epilepsy is 12.5 per 1000(range, 5 to 57 per 1000), and the annual incidence ranges rom 78 to 190per 100,000. Furthermore, the paerns o age-specic incidence are quitediferent in developing countries, where incidence peaks in young adults, notin elderly people. Risk Factors  Among all age groups, the top ve risk actors or developing acute symptom-atic seizures are head trauma (16%), stroke (16%), inectious disorders(15%), toxic-metabolic disorders (15%), and drug and alcohol withdrawal(14%) (able 410-1).Te risk actors or developing epilepsy difer in adults and children. Inchildhood, excluding inherited epilepsies, the risk is increased by ebrile sei-zures, head trauma, inections o the brain, mental retardation, cerebral palsy,and aention-decit hyperactivity disorder. Perinatal insults do not carry anincreased risk or epilepsy unless they are accompanied by mental retardationor cerebral palsy.In adults, risk actors or developing epilepsy can be identied in only onethird o patients, in whom head trauma, brain inections, stroke, and Alzheim-er’s disease are the most common. Te risk o developing epilepsy is increasedmore than 500-old by a history o a military head injury, 30-old by a severecivilian head injury (Chapter 406), 20-old each by stroke (Chapter 414) and brain inections (Chapters 420 and 422), and 10-old each or Alzheimer’sdisease (Chapter 409), migraine headache (Chapter 405), and hypertension. 410 THE EPILEPSIES SAMUEL WIEBE DEFINITION  A  seizure is dened by transient ocal or generalized signs or symptoms dueto abnormal excessive or synchronous neuronal activity in the brain. Focalseizures  , which srcinate within neuronal networks limited to one cerebral  CHAPTER   410 THE EPILEPSIES 2284 TABLE 410-1 COMMONCAUSESOFACUTESYMPTOMATIC(PROVOKED)SEIZURES METABOLIC Hypernatremia, hyponatremia, hypocalcemia, hypoxia, hypoglycemia, nonketotichyperosmolar hyperglycemia, renal ailure DRUG INDUCED Teophylline, meperidine, tricyclic antidepressants, ephedra, gingko, phenothiazines,quinolones, β -lactams, isoniazid, antihistamines, cyclosporine, intererons,tacrolimus, cocaine, lithium, amphetamines DRUG WITHDRAWAL  Alcohol, benzodiazepines, barbiturates ENDOCRINE Hyperthyroidism, hypothyroidism, peripartum OTHER SYSTEMIC CONDITIONS Sickle cell crisis, hypertensive encephalopathy, systemic lupus erythematosus,polyarteritis, eclampsia, high ever CENTRAL NERVOUS SYSTEM DISORDERS rauma, stroke, intracerebral hemorrhage, encephalitis, abscess, bacterial meningitis FIGURE 410-1.  Selected electroencephalogram channels showing a typical right anterior temporal spike, the archetypal interictal footprint of temporal lobe epilepsy. Thepatienthadrighthippocampalsclerosis. In Latin America, the most requently identied risk actor is brain inection.In endemic areas, neurocysticercosis (Chapter 362) accounts or about 10%o all newly diagnosed cases o epilepsy. Pathobiology Pathogenesis Te pathologic substrates and mechanisms underpinning initiation and prop-agation difer or ocal and generalized seizures. In ocal seizures, an aggregateo cortical or subcortical neurons develop high-requency bursts o sodium-dependent action potentials caused by a shi in calcium conductance,thereby resulting in the typical EEG spike discharge (Fig. 410-1). Spread o  bursting activity to other neurons is normally prevented by surroundinginhibitory mechanisms, such as hyperpolarization and inhibitory interneu-rons. When a sucient number o neurons are engaged in sustained bursting,urther excitatory phenomena ensue, including the increased release o excitatory neurotransmiers owing to presynaptic accumulation o Ca 2 +  ,depolarization o surrounding neurons owing to increased extracellular K  +  ,and urther neuronal activation caused by depolarization-induced activationo   N  -methyl- d -aspartate (NMDA) receptors. As excitation increases andinhibition decreases, additional neurons are recruited regionally and dis-tantly, thereby resulting in seizure propagation. Te mechanisms by whichneurons develop a tendency toward anomalous bursting activity includealterations in neurotransmiers, membrane receptors, ion channels, second-messenger systems, and gene expression o various proteins.Considerably less is known about the basic mechanisms underlying gen-eralized seizures, which depend prominently on thalamocortical circuits. Inabsence seizures, the classic generalized spike-and-wave discharges seen onEEG (Fig. 410-2) are related to alterations in oscillatory rhythms generated by circuits that connect the thalamus and cortex and that involve -type Ca 2 +  channels, which are located in the reticular nucleus o the thalamus. In gen-eralized convulsive seizures, cortical neurons exhibit prolonged depolariza-tion during the tonic phase, ollowed by rhythmic depolarization andrepolarization during the clonic phase. Activation o NMDA receptorsincreases calcium Ca 2 + inux, thereby leading to urther neuronal excitation.Te initiation and modulation o generalized convulsive seizures involve cho-linergic, noradrenergic, serotonergic, and histaminergic aferents rom the brain stem and basal orebrain structures, which modulate excitability o hemispheric motor mechanisms. Genetics Only 15% o patients have one or more rst-degree relatives who also suferrom epilepsy, and o those, about 75% have just one afected relative.However, the risk is still higher in rst-degree relatives o patients with epi-lepsy than in the general population. In a large population-based study, thecumulative incidence o epilepsy to age 20 years was 2.5-old higher in sib-lings and 3.4-old higher in ofspring o patients with epilepsy.Te genetic aspects o epilepsy can be categorized in three large groups: Conditions in which epilepsy forms part of a mendelian disorder  include over200 rare conditions, which encompass neurocutaneous disorders (Chapter426), neurodegenerative disorders, inherited malormations o corticaldevelopment (Chapter 426), and inherited metabolic disorders. For example,genes have been identied in progressive myoclonic epilepsies (e.g.,Unverricht-Lundborg disease, Laora’s disease, and the neuronal ceroid lipo-uscinosis), X-linked myoclonic epilepsy with mental retardation, and corti-cal malormation syndromes, such as polymicrogyria, pachygyria, andperiventricular nodular heterotopia.  CHAPTER   410 THE EPILEPSIES 2285 expression; i consciousness or awareness is predominantly impaired, they are reerred to as dyscognitive seizures. For example, patients who ormerly  were classied as having simple partial seizures now are classied as havingocal seizures with preserved consciousness. An aura consists o sensory, autonomic, or psychic symptoms that areexperienced at the start o an observable seizure. Te aura is a ocal seizureitsel, and it is oen missed because patients and clinicians ocus on the moredramatic dyscognitive or convulsive seizure that ollows. Careul inquiry about the occurrence o an aura is o crucial importance or three reasons.First, it points to a ocal as opposed to a generalized onset, thereby implyingan underlying ocal structural or unctional brain abnormality (e.g., a tumor)that requires urther investigation. Second, ocal seizures have importantimplications or therapy and or prognosis (see later). Tird, the nature o thesymptoms points to the area o the brain that gives rise to the seizure and thatcould be a target or surgical treatment.Te neuronal discharge causing the ocal seizure may remain conned tothe region where it began (as an aura or more objective ocal event), or it may spread to involve additional brain areas. Tus, a ocal seizure srcinating inthe cortical area that represents sensation o the hand (rolandic area) may  begin with contralateral hand tingling and then progress to involve additionalcortical regions ipsilaterally, producing more extensive sensory symptoms as well as clonic motor signs. Seizures o rolandic srcin in particular exhibit apeculiar type o propagation, in which the seizure activity “marches” romhand to arm to leg area ipsilaterally, a process reerred to as a jacksonianmarch. Aer the clonic motor activity ends, patients are oen weak; a post-ictal or odd’s paralysis may last hours or even a day or two, with gradualresolution. Te seizure may also propagate to distant ipsilateral or contralat-eral regions along known anatomic pathways.In dyscognitive seizures, seizure propagation suciently involves limbicand bilateral structures to cause alteration o consciousness . Focal seizuressrcinating rom any region can become dyscognitive seizures, and unilateralocal seizures can progress to involve bilateral brain areas and cause a convul-sive seizure. Such convulsive seizures usually take the orm o generalizedtonic-clonic events rather than another type o generalized seizure (able410-3).Te evolution o the ocal clinical seizure reects the evolution o the EEGchanges, which in turn reects the pathophysiology o the process. A  FIGURE 410-2.  Electroencephalogram pattern of 3-Hz generalized spike and wave, the characteristic correlate of generalized absence seizures. Thisepisodelasting6secondshadnodiscernibleclinicalmanifestations.  Epilepsies that can be directly explained by simple mendelian inheritance arerare and account or only about 1% o all epilepsy cases. More than a dozengenes have been identied in the ollowing eight autosomal dominant epi-lepsy syndromes, o which all but two encode voltage-gated or ligand-gatedion channels. Benign amilial neonatal seizures are associated with mutationsin the potassium-channel genes  KCNQ2 and  KCNQ3 . Benign amilialneonatal-inantile seizures are associated with mutations in the sodium-channel SCN2A . Generalized epilepsy with ebrile seizures plus is associated with mutations in the genes or sodium-channel subunits SCN1A  , SCN1B  ,and SCN2A and the GABRG2 subunit o the GABA   A  receptor. Childhoodabsence epilepsy with ebrile seizures is associated with mutations in the GABRG2 subunit o the GABA   A  receptor. Autosomal dominant juvenilemyoclonic epilepsy has been associated with a mutation in the GAB1  subunit o the GABA   A  receptor and in  EFHC1  , which regulates calcium cur-rents. Autosomal dominant idiopathic generalized epilepsy is associated withmutations in the chloride-channel gene CLCN2 . In autosomal dominant noc-turnal rontal lobe epilepsy, mutations have been ound in the genes encodingnicotinic acetylcholine receptor subunits CHRNA4 and CHRNB2 . In auto-somal dominant partial epilepsy with auditory eatures, mutations have beenound in the  LGI1 gene, which appears to be involved in development o thecentral nervous system (CNS).In some patients, the epilepsy is associated with “complex” disease genes. Inthis large group, which constitutes about 50% o all patients with epilepsy,multiple genes with individually small but additive efects act in combination with environmental actors to produce an increased risk or epilepsy. CLINICAL MANIFESTATIONS Te clinical expression o seizures varies widely depending on the type o seizure and the areas o the brain that are involved by the epileptic activity. Accurate identication o the specic types o seizures determines the syn-drome and dictates the type o drug that the patient should receive. Focal Seizures Focal seizures srcinate within neuronal networks limited to one area o onecerebral hemisphere and produce signs and symptoms corresponding to theunction subserved by the area o cerebral cortex engaged by the seizure(able 410-2). Focal seizures are now subclassied according to their clinical  CHAPTER   410 THE EPILEPSIES 2286 TABLE 410-2 CLINICALMANIFESTATIONSOFDIFFERENTTYPESOFFOCALSEIZURESANDAREASOFTHEBRAININVOLVED SEIZURE TYPE AREAS OF BRAIN INVOLVED CLINICAL EXPRESSION SomatosensoryPostcentral rolandic; parietalContralateral intermient or prolonged tingling, numbness, sense o movement, desire to move, heat, cold,electric shock. Sensation may spread to other body segments.ParietalContralateral agnosia o a limb, phantom limb, distortion o size or position o body partSecond sensory; supplementary sensory-motorIpsilateral or bilateral acial, truncal or limb tingling, numbness, or pain. Oen involve lips, tongue, ngertips,eetMotorPrecentral rolandicContralateral regional clonic jerking, usually rhythmic, may spread to other body segments in jacksonian motormarch. Oen accompanied by sensory symptoms in same areaSupplementary sensory-motorBilateral tonic contraction o limbs causing postural changes, may exhibit classic encing posture, may havespeech arrest or vocalizationFrontalContralateral head and eye version, salivation, speech arrest or vocalization; may be combined with othermotor signs (as above) depending on seizure spread AuditoryHeschl’s gyrus—auditory cortex insuperior temporal lobeBilateral or contralateral buzzing, drumming, single tones, mued soundsOlactoryOrbitorontal; mesial temporal cortexOen described as unpleasant odorGustatoryParietal; rolandic operculum; insula;temporal lobeOen unpleasant taste, acidic, metallic, salty, sweet, smoky  VertiginousOccipitotemporal-parietal junction;rontal lobeSensation o body displacement in various directions VisualOccipitalContralateral static, moving, or ashing colored or uncolored lights, shapes, or spots. Contralateral or bilateral,partial or complete loss o vision.emporal; occipitotemporal-parietal junctionFormed visual scenes, aces, people, objects, animalsLimbicLimbic structures: amygdala,hippocampus, cingulum, olactory cortex, hypothalamus Autonomic: abdominal rising sensation, nausea, borborygmi, ushing, pallor, piloerection, perspiration, heartrate changes, chest pain, shortness o breath, cephalic sensation, lightheadedness, genital sensation, orgasmPsychic: déjà vu, jamais vu, depersonalization, derealization, dreamlike state, orced memory or orced thinking,ear, elation, sadness, sexual pleasure, hallucinations or illusions o visual, auditory, or olactory natureDyscognitiveUsually bilateral involvement o limbic structures (see above)Previously known as “complex partial seizures,” characterized by a predominant alteration o consciousness orawareness. Te current denition requires involvement o at least two o ve components o cognition:perception, aention, emotion, memory, and executive unction.  Note: Focal seizures may evolve into bilateral convulsive seizures. TABLE 410-3 GENERALIZEDSEIZURES:CLASSIFICATIONANDCLINICALEXPRESSION SEIZURE TYPE SUBTYPE CLINICAL EXPRESSION  AbsenceypicalAbrupt cessation o activities, with motionless, blank stare and loss o awareness lasting about10 seconds. Te aack ends suddenly,and patient resumes normal activities immediately. AtypicalLonger duration than typical absence, oen accompanied by myoclonic, tonic, atonic, and autonomic eatures as well as automatisms With myocloniasAbsence with myoclonic components o variable intensity MyoclonicMyoclonicSudden, brie ( < 100 msec), shocklike, involuntary, single or multiple contractions o muscle groups o various locationsMyoclonic AtonicA sequence consisting o a myoclonic ollowed by an atonic phaseMyoclonic onicA sequence consisting o a myoclonic ollowed by a tonic phaseonicSustained increase in muscle contraction lasting a ew seconds to minutesClonicProlonged, regularly repetitive contractions involving the same muscle groups at a rate o 2-3 cycles per second AtonicSudden loss or diminution o muscle tone lasting 1-2 seconds, involving head, trunk, jaw or limb musculatureonic-clonicA sequence consisting o a tonic ollowed by a clonic phase simultaneous rhythmic, localized discharge (oen in the 4- to 7-Hz range) becomes higher in amplitude and lower in requency as the seizure continues(Fig. 410-3). Some seizures that begin in the association cortex (e.g., rontalor parietal lobes) have bizarre or extremely brie clinical maniestations, without postictal decits, and create diagnostic challenges. Te stereotypednature o the clinical events, with the identication o EEG changes i present,may be the only way to make an appropriate diagnosis. Te diagnosis can beeven more challenging i the seizure spreads to diferent cortical regionsduring diferent seizure episodes, thereby producing variable constellationso clinical ndings at diferent times.Focal seizures with or without dyscognitive eatures can also occur as aseries o single events without intervening normal behavior, thereby resultingin ocal status epilepticus. Focal status epilepticus with dyscognitive seizuresis characterized by prolonged conused behavior. EEG ndings may benormal in a ocal seizure without altered awareness, even in patients withstatus epilepticus, but the diagnosis is usually evident rom the clinical ea-tures. In status epilepticus o ocal dyscognitive seizures, EEG recordingsshow continuous abnormalities that are not o the same nature as seen insingle seizures in that individual. Te most common are a slow background with superimposed rhythmic high-amplitude sharp waves or repetitive rhyth-mic seizure discharges (Fig. 410-4). Tis type o status epilepticus is mostrequent with rontal lobe seizures but can occur in temporal lobe seizures as well. Te actors that precipitate status epilepticus are not well dened, norare the implications or treatment or prognosis.Nonconvulsive status epilepticus consists o a state o conusion orimpaired mental status in patients with various neurologic diagnoses (i.e.,trauma, stroke) in the acute intensive care unit seing. It also denotes a condi-tion that can occur de novo in older adults without a precipitating cause andthat is characterized by prolonged conusional episodes, which are caused by generalized slow spike-and-wave status epilepticus. Clinical suspicion shouldprompt an EEG study, which is essential or diagnosis (Fig. 410-5). Generalized Seizures Generalized seizures rapidly afect both cerebral hemispheres, and their clini-cal expression is consistent with substantial involvement o both sides o the brain (see able 410-3). Convulsive seizures, which are also reerred to asgrand mal seizures, consist o excessive, abnormal muscle contractions thatmay be sustained or interrupted, and usually are a combination o tonic and
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