Injury Due to Ionizing Radiation General Aspects Radiation therapy can injure the brain, the spinal cord, and the periph- eral nerves. The extent of injury de- pends on: the radiation dose per session and the total dose, the treatment field, and the timing of the treatment sessions. An empirical measure of the injurious potential of radiation therapy is given by the NSD (normalized standard dose), which is calculated according to the following formula: NSD RET =TD×N –0.24 ×T 0.11 Here the NSD is expressed in RET (rad equivalent therapy), TD stands for the total dose in rads, Nthenumber of in- dividual doses, and T the duration of treatment. The latency of radiation injury may be months or years, de- pending on the NSD. Radiation Injury to the Brain Mechanism Radiation necrosisofthebrainmay occur with a dose of 2800 rad (28 Gy) or more. As already mentioned, the extent and latency of radiation injury are stronglydose-dependent. Pathological Anatomy Fibrinoid necrosis of blood vessels, with extravasation of plasma and erythrocytes, is accompanied by lym- phocytic infiltration and massive ne- crosis of nervous tissue, particularly in the white matter. Differential Diagnosis Because radiation therapy is usually given to treat a tumor, radiation ne- crosis of the brain generally requir es differentiation from recurrent tumor. Cerebral ischemia is sometimes the indirect result of radiation therapy , when it is due to radiation-induced occlusion of large vessels such as the middle cerebral artery or the internal carotid artery in the neck. Radiation Injury to the Spinal Cord The spinal cord, too, like the brain, can be injured by either conventional photon-beam orhigh-energy electron-beam radiotherapy. Signs of spinal cord dysfunction generally ap- pear only if the dose used is 3500 rads or higher, given over a period of 28 days or less. Radiation myelopathy has been described after radiotherapy for tumors of the pharynx and neck, lymphoma, mediastinal tumors, and lung tumors. It mostcommonlyarises about 1 year after treatment, though the latency may vary from 2 months to 5 y ears, and rarely longer.Thepa- thoanatomic changes, which mainly affect the white matter of the spinal cord, consist of spongiform demyelin- ation withastroglialreactioninthe early phase, and focal or diffuse de- myelinationwithnecrosisinlater phases. Vessel walls are regularly af- fected by changes ranging from fibri- noid necrosis with extravasation to telangiectasis. The neurons are often relatively well preserved. 490 6InjurytotheNervousSystembySpecificPhysical Agents Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. Clinical Features The clinical presentation ofradiation myelopathy is highly varied. Cervical myelopathy,themostcommon syn- drome, usually presents with pares- thesiae in the legs, which may remain the only symptom or may later be ac- companied by Lhermitte’s sign (which usually resolves spontaneously). Other patients suffer from progressive para- orquadriparesis.More than half of all patients develop a more or less pure Brown-S´equard syndrome. Pro- prioception is disturbed more often than superficial sensation. There is some evidence that radiation therapy may induce a form of myelitis accompanied by myoclonus in the lower limbs. This process, when it oc- curs, may remain stable at a relatively mild degree of severity, but unfortu- nately tends to progress to a more or less complete spinal cord transection syndrome over a period of weeks to months. About half of the affected pa- tients die months or years later from the complications of the myelopathy, while in others the myelopathy can remain stable or even regress. Treatment In the absence of an etiologic treat- ment, only symptomatic treat- ments are available, e.g., carbame- zepine to relieve dysesthesia. Radiation Injury to the Peripheral Nervous System See p. 764. Hypothermic Injury General Aspects Generalized hypothermia is rarely the result of cold exposure alone; usually other f actors are atworkthathave rendered the patient unable to pro- tect himself adequately against the cold (e.g., alcohol or drug abuse or mental illness). Clinical Features Central nervous system. The depth of hypothermiadetermines the extent to which the patient’s consciousness is impaired and his pulse, blood pres- sure, and respiratory rate are de- pressed. Severe hypothermia can cause cardiac arrest. The pupillary re- flexes and the intrinsic muscle re- flexes are diminished, while muscle tone may be increased, and pyrami- dal tract signs may appear. Meningis- mus may develop even though the CSF is normal. If thepatientsurvives, there are generally no permanent neurologic sequelae other than those associated with the underlying ill- ness, if any. Peripheral nervous system. Animal experiments have shown that hypo- thermia alters the fine structure of peripheral nerves and causes a slow- ing or blockade of impulse conduc- tion. Weakness and sensory distur- bances due to hypothermic periph- eral nerve injuries were described in soldiers who fought in the trenches during the two World Wars, and in shipwreck survivors. The thick, mye- linated fibers are most susceptible to Hypothermic Injury 491 Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. this type of injury. Myocardial cooling during open heart surgery causes hy- pothermic injury to the phrenic nerve in 7% of cases; such injuries are not always fully reversible. Treatment Resuscitation and warming are the essential components of treatment for hypothermia. Severely hypo- thermic patients may be re- warmed by extracorporeal cardio- pulmonary bypass,ifnecessary (993a). Therapeutic success is pos- sible even in cases of extremely deep hypothermia (343b). 492 6InjurytotheNervousSystembySpecificPhysical Agents Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. 7 Epilepsy, Other Episodic Disorders of Neurologic Function, and Sleep Disorders Epilepsy Definition: Epilepsy is characterized by attacks of impaired neurologic function, nearly always combined with loss of consciousness and/or other paroxysmal motor, sensory, or autonomic phenomena. Each seizure is produced by an abnormal electrical excitation of brain tissue that can usually be detected during the seizure as an abnormal pattern on the electroencephalogram (EEG). There are different types of epilepsy that are caused by different structural and functional (metabolic) anomalies of the brain. History Epilepsy was well known in the an- cient world, both inmedicalpractice and in everyday life. The Greek term epilepsia is derived from the verb epilambanein, “to lay hold of, seize, attack” (cf. English seizure). It is easy to see how the sufferer’s obvious lack of self-control during the fit or sei- zure gave rise, in many different cul- tures, to the notion of possession by asupernatural b eing – either an evil spirit or, sometimes, a beneficent one. The Latin term morbus sacer (“the holy disease”) reflects this primitive conception. Yet Hippo- crates, the founder of rational medi- cine (5th–4th cent. BC), already un- derstood epilepsy correctly as the product of a sick brain. The notion of epilepsy as divine punishment pre- vailed once again throughout the Christian Middle Ages and was not definitively discarded until the En- lightenment. The Swiss physician Samuel Auguste Tissot described practically all forms of epilepsy in his Trait ´edel’´epilepsie of 1770 (491a). The British neurolo- gist John Hughlings Jackson proposed in 1873 that epilepsy was due to ex- cessively strong electrical discharges of the gray matter ofthebrain. Two years later, inLiverpool,Richard Caton was able to confirm this hypothesis by direct measurement of cerebral electrical activity in rabbits and mon- keys. In this era, too, the antiepileptic activity of bromide was discovered (1857). Further antiepileptic drugs were de- veloped in the firsthalfofthe20th century – phenobarbital in 1912 and diphenylhydantoin (phenytoin) in 1938. The first human EEG was re- corded by Hans Berger of Jena, Ger- many, in 1924 (who gave due credit to Caton). By mid-century, the Montreal neurosurgeon Wilder Penfield, in col- laboration with the neurologists Her- Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. 140 120 100 80 60 40 20 <1 1–5 6–10 11–15 >16–64* >65* C ases per 100 000 persons per year Y ea r s 118 48 43 21 56 139 Fig. 7.1Incidenceof epilepsybyage(after Schmidt and Elger; data from Camfield et al. and Forsgren et al.). The incidence of epi- lepsy is highest in the first year of life and after age 65, and low- est in early adulthood. bert Jasper and William Lennox, had succeeded in using direct intraoperat- ive observation andelectroencepha- lography to correlate the normal func- tion of various brain regions with the clinical phenomenology of epilepsy. Etiology and Pathogenesis Etiology In principle, any brain – even a healthy one – can generate an epilep- tic seizure under certain conditions that render the gray matter unusually excitable. A single febrile seizure in early childhood, for instance, does not qualify as “epilepsy.” The term, in its proper sense, refers to a lasting ten- dency to generate seizures. The cause may be a structural abnormality of the brain, such as a developmental anomaly, a scar due to trauma during the birth process or at any later time, ischemia, focal infection, or tumor. In other cases, epilepsy is due to a meta- bolic disturbance, such as hypoglyce- mia, or to a toxic condition, such as alcoholism. The cause of epilepsy of- ten r emains unidentified. Pathogenesis Epilepsy reflects the abnormal func- tioning of cerebral neurons. In gen- eral, a neuron receives both excit- atory and inhibitory influences from other neurons, and fires an action po- tential only when the overall effect of the excitatory postsynaptic potentials (EPSPs) outweighs that of the inhibi- tory postsynaptic potentials (IPSPs). Intraneuronal recordings from epi- leptic foci have revealed a membrane depolarization of abnormally high amplitude that provokes the firing of aseriesofactionpotentials at high frequency, followed by hyperpolar- ization. This type of electrical event, which can be considered a giant EPSP, is called a paroxysmal depolarization shift (PDS). APDSoccurringinthemidstofa population of neurons is reflected on the EEG by spikes followed by a slow wave (spike-wavecomplex).Such complexes may be the initial EEG cor- relate of a clinically observable sei- zure. It is not yetknownwith cer- tainty where these complexes arise; thalamocortical and intracortical 494 7Epilepsy, Other Episodic Disorders of Neurologic Function, and Sleep Disorders Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. Fp F C P N asion Inion O 20% 20% 20% 10% 10% 20 % a Fig. 7.2a–d Electrode placement in the 10-20 system (a–c from K.F. Masuhr and M. Neumann, Neurologie (Stuttgart: Hippokrates, 1992); d from H. Kunkel, Das EEG in der neurologischen Diagnostik, in H. Schliack, H.C. Hopf, Diagnostik in der Neurologie (Stutt- gart: Thieme, 1988). The EEG recording from any given electrode reflects the electrical ac- tivity of the underlying brain area. Fig. 7.2b–d generation have both been hypothe- sized. The following processes play an important role in neuronal depolar- ization and repolarization: calcium and sodium influx and po- tassium efflux, excitatory amino acids such as glu- tamate, and inhibitory neurotransmitters such as GABA. These processes are the basis of vari- ous kinds of anticonvulsant therapy. Some medications lessen the sodium influx, others potentiate GABA-ergic inhibition, and others selectively block calcium channels. Epidemiology Epilepsy is one of the more common types of neurologic disease. It affects 0.5% to 1% of persons. The o nset of epilepsy is more common in the first year of life and after age 65 (Fig. 7.1). Persons with affected family mem- bers are morelikelytodevelop epi- lepsy. If one parent suf fers from idio- pathic epilepsy, the child’s risk is 1:25; if one parent suffers from symptomatic epilepsy, the child’s risk is 1 : 67. The risk is higher than 1 : 25 if both parents are affected. a Lateral aspect. The electrodes are mounted at the specified intervals between the nasion and the inion. Ancillary Diagnostic Tests in Epileptology We will first discuss the moreimpor- tant diagnostic tests before proceed- ing to the classification and clinical features of epilepsy. Electroencephalography (320, 491,708) EEG, the most important diagnostic study in epileptology, provides infor- mation about the function,rather Epilepsy 495 Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. C 2 Fp1 F7 T3 T5 O1 C3 T3 T4 C4 b c 20% 10% 10 % 20% 20% 20% 20% 20% 20% 10% 20% 10% b Frontal aspect. The preauricular points are the reference sites for the placement of the central transverse row of electrodes. C2 is the intersection of the central transverse and longitudinal rows. c Superior aspect. 496 7Epilepsy, Other Episodic Disorders of Neurologic Function, and Sleep Disorders Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. Preauricula r point Preauricular point x Point of measurement d Nasion Ini o n Fp1 Fp2 Fpz 10% 10% 20%20% 20% 20% 10% 20% 20% Fz Cz F7 T3 xx A1 A2 T4 T6T5 O2 O1 Oz C3 C4 F4F3 Pz P4P3 F8 d The names of the electrodes in the 10–20 system. than the structure, of the brain. It reg- isters changes in electrical potential that represent the net effect of the EPSPs and IPSPs in the cerebral cor- tex. It also indirectly reflects the func- tion of the thalamus a nd the mid- brain reticular formation, which are responsible for the maintenance of the sleep-wake cycle. The standard EEG is recorded through electrodes mounted on the scalp ac- cording to the 10–20 system (Fig. 7.2). It is a general property of electrical potential that it is not well-defined as an absolute quantity, but can only be measured as a difference between two points. Thus, the EEG is obtained either as a bipolar recording (in which potential differences are measured between the scalp electrodes) or as a so-called monopolar recording (in which the difference is measured be- tween each scalp electrode and a ref- erence electrode). The ECG is re- corded simultaneously with the EEG on the same sheet of paper. Potential differences at thescalpare on the order of 10–100 V, while po- tential differences at the surface of the brain (without the attenuation produced by the skull and scalp) are about ten times higher. EEG activity in different frequency ranges is con- ventionally designated by Greek let- ters, as follows: sub- waves, 1Hz; waves, from 1 Hz up to (but not including) 4 Hz; waves, from 4 Hz to 8 Hz; waves, from 8 Hz to 1 3 Hz; waves, 13 Hz. The normal EEG in the awake adult with eyes closed consists of sinusoi- dal oscillations in the range of 8–13 Hz (i.e., rhythm), maximally intense over the occipital lobes. Faster ( )activityisseenoverthe Epilepsy 497 Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. β waves α waves 1s θ waves δ waves Fig. 7.3EEGrhythmsinvarious frequency ranges. Table 7.1 Pathological EEG rhythms and their clinical significance EEG finding Clinical significance Focal slow activity Localized cerebral lesion – e.g., infarct, hemorrhage, tumor, abscess, encephalitis Intermittent, rhythmic slow waves Thalamocortical dysfunction; metabolic or toxic distur- bance, obstructive hydrocephalus, deep-seated pro- cess near the midline, posterior fossa lesion; a nonspe- cific finding in patients with generalized epilepsy Generalized arrhythmic and polymorphic slow activity Diffuse encephalopathy of metabolic, toxic, infectious, or degenerative origin Epileptiform discharges – e.g., focal or generalized spikes, sharp waves, or spike-slow- wave complexes Focal or generalized epilepsy (or clinically silent predis- position to seizures) Low-voltage activity Hypoxic-ischemic brain injury, degenerative brain dis- ease, extra-axial lesion such as subdural hematoma (focal low voltage) Flat-line EEG Consistent with, but not diagnostic of, death (“brain death”) 498 7Epilepsy, Other Episodic Disorders of Neurologic Function, and Sleep Disorders Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. [...]... Automatisms (Cont.) 1 Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license Epilepsy 503 Table 7.2 Classification of epileptic seizures as proposed by the International League Against Epilepsy (continued) 1.3 Partial seizures with secondary development of generalized tonic-clonic (GTC) seizures (= GTC seizures with partial or focal onset; partial seizures... consumption, and blood volume and can thus be used as a test of brain function It makes use of radioactive tech- Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license Epilepsy netium or iodine compounds as tracers – e.g., 99mTc-HMPAO or 133I-iodoamphetamine (IMP) Central benzodiazepine receptor ligands such as 11Cflumazenil can be used to detect areas... atonic seizures are the main types of seizure that cause falls | Partial (= Focal) Seizures The terms “partial” and “focal” seizure are synonymous Seizures of this type are caused by a focal abnormality in the brain and are not associated with a loss of consciousness or with a generalized tonic-clonic convulsion Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions... postictal changes are nonspecific) Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license Epilepsy Any particular type of seizure may have a number of possible causes and may be found in multiple epilepsy syndromes Thus, the diagnosis of the particular epilepsy syndrome that is present requires not only a phenome- Aura Simple focal seizures, complex... during pregnancy is more common than that of eclamptic seizures and usually occurs between the 26th and 36th weeks of gestation Epileptic seizures in the puerperal period may be a manifestation of cerebral venous or venous sinus thrombosis (p 545) Pregnant women should be treated pro- Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license 7 Epilepsy, Other... number of other, rarer epilepsy syndromes: > juvenile absence epilepsy, > myoclonic-astatic epilepsy, > juvenile myoclonus epilepsy, Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license Fig 7.7 EEG in absence epilepsy Generalized 3–4 Hz spikes... continuous, generalized spike-wave activity on their sleep-EEG (711c); the seizures apparently stop spontaneously once these patients reach adulthood (243b) A further type of benign childhood epi- 523 lepsy (the Panayiotopoulos type), which constitutes one of the occipital lobe epilepsy syndromes, has a similarly favorable course ( 166 b) Children with this syndrome have partial seizures with ictal vomiting,... symptomatic epilepsy Epileptic Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license 502 7 Epilepsy, Other Episodic Disorders of Neurologic Function, and Sleep Disorders Table 7.2 Classification of epileptic seizures as proposed by the International League Against Epilepsy 1 Partial (focal, localized) seizures 1.1 Simple partial seizures (without alteration... become secondarily generalized) Simple partial seizures involve either motor or sensory phenomena (or both), while complex partial seizures, by definition, involve an altered state of consciousness, perhaps with automatisms and autonomic manifestations as well A partial seizure of either type may become secondarily generalized | Simple Partial Seizures Simple partial seizures are the expression of... with delirium tremens have epileptic seizures, usually before the delirium sets in, and usually 12 or Fig 7 .6 Interictal EEG in a patient with grand mal epilepsy Paroxysmal, generalized, partially atypical spikes and waves are seen simultaneously in all leads 510 Mumenthaler, Neurology © 2004 Thieme All rights reserved Usage subject to terms and conditions of license Epilepsy more hours after the last . Her- Mumenthaler, Neurology © 2004 Thieme All rights reserved. Usage subject to terms and conditions of license. 140 120 100 80 60 40 20 <1 1–5 6 10 11–15 > 16 64 * > ;65 * C ases per 100. iodine compounds as trac- ers – e.g., 99m Tc-HMPAO or 133 I-iodo- amphetamine (IMP).Centralbenzodi- azepine receptor ligands such as 11 C- flumazenil can be used to detect ar- eas of neuronal damage. frontobasal cortex. Pa- tients usually also manifest automa- tisms, such as the stereotyped repeti- tion of a particular movement, rub- bing or wiping movements, chewing, lip-licking, lip-smacking, or