Porth's Essentials of Pathophysiology, 4e

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Nervous System

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(typical, atypical, myoclonic absence, absence of eyelid myoclonia), myoclonic seizures (myoclonic, myoclonic atonic, myotonic clonic), clonic seizures, tonic seizures, and atonic seizures (Chart 37-1). 60 Tonic-Clonic Seizures. Tonic-clonic seizures, formerly called grand mal seizures, are the most common major motor seizures. 60 Frequently, a person has a vague warn- ing (probably a simple focal seizure) and experiences a sharp tonic contraction of the muscles with extension of the extremities and immediate loss of consciousness. Incontinence of bladder and bowel is common. Cyanosis may occur from contraction of airway and respiratory muscles. The tonic phase is followed by the clonic phase, which involves rhythmic bilateral contraction and relax- ation of the extremities. At the end of the clonic phase, the person remains unconscious until the RAS begins to function again. This is called the postictal phase. The tonic-clonic phases last approximately 60 to 90 seconds. Absence Seizures. Absence seizures are generalized, nonconvulsive epileptic events and are expressed mainly as disturbances in consciousness. 60 Formerly referred to as petit mal seizures, absence seizures typically occur only in children and cease in adulthood or evolve to generalized motor seizures. Children may present with a history of school failure that predates the first evidence of seizure episodes. Although typical absence seizures have been characterized by a blank stare, motionless- ness, and unresponsiveness, motion occurs in many cases of absence seizures. This motion takes the form of automatisms such as lip smacking, mild clonic motion (usually in the eyelids), increased or decreased postural tone, and autonomic phenomena. There often is a brief loss of contact with the environment. The seizure usually lasts only a few seconds, and then the child is immedi- ately able to resume normal activity. The manifestations often are so subtle that they may pass unnoticed. Atypical absence seizures are similar to typical absence seizures except for greater alterations in muscle tone and less-abrupt onset and cessation. In practice, it is difficult to distinguish typical from atypical absence seizures without the benefit of supporting EEG findings. However, it is important to distinguish between com- plex focal and absence seizures because the drugs of choice for treatment are different. Medications that are effective for focal seizures may increase the frequency of absence seizures. Myoclonic Seizures. Myoclonic seizures involve brief involuntary muscle contractions induced by stimuli of cerebral origin. A myoclonic seizure involves bilateral jerking of muscles, generalized or confined to the face, trunk, or one or more extremities. Tonic seizures are characterized by a rigid, violent contraction of the mus- cles, fixing the limbs in a strained position. Clonic sei- zures consist of repeated contractions and relaxations of the major muscle groups. Tonic Seizures. Similar to the tonic phase of tonic–clonic seizures, tonic seizures are characterized by contraction of the voluntary muscles so that the body stiffens with

hemisphere or the other. They may originate in subcorti- cal structures, and may be discretely localized or widely distributed. For each seizure type, the site of onset is consistent from one seizure to another, with preferential propagation patterns that can involve the contralateral hemisphere. 60 Focal seizures are described according to their manifestations; that is, they may occur without or with impairment of consciousness or awareness. Focal Seizures Without Impairment of Conscious­ ness orAwareness. This type of seizure usually involves one hemisphere and is not accompanied by loss of con- sciousness or awareness. The observed clinical signs and symptoms depend on the area of the brain where the abnormal electrical activity is taking place. There may be involuntary motor movements; somatosensory dis- turbances, such as tingling and crawling sensations; or special sensory disturbances, such as visual, auditory, gustatory, or olfactory phenomena. When abnormal cortical discharge stimulates the autonomic nervous sys- tem, flushing, tachycardia, diaphoresis, hypotension or hypertension, or pupillary changes may be evident. 60 This type of focal seizure may be preceded by an aura, a term that has traditionally been used to describe the stereotyped warning sign of an impending seizure activity described by the affected person. The aura actu- ally represents a simple partial seizure, affecting only a small area of electrical activity. A history of an aura is clinically useful to identify the seizure as focal and not generalized in onset. However, absence of an aura does not reliably exclude a focal onset because many focal seizures generalize too rapidly to generate an aura. Focal Seizures with Impairment of Consciousness. These types of seizures, which arise from the tempo- ral lobe, involve impairment of consciousness. 60 The seizure begins in a localized area of the brain but may progress rapidly to involve both hemispheres. These sei- zures, sometimes referred to as psychomotor seizures, are often accompanied by automatisms or repetitive non-purposeful activities such as lip smacking, gri- macing, patting, or rubbing clothing. Confusion dur- ing the postictal period (after a seizure) is common. Hallucinations and illusional experiences such as déja vu (a sense of unfamiliarity with a known environment) have been reported. There may be overwhelming fear, uncontrolled forced thinking or a flood of ideas, and a feeling of detachment and depersonalization. A person with this type of seizure disorder may be misdiagnosed as having a psychiatric disorder. Generalized Seizures Generalized-onset seizures are the most common type in young children. The seizures are classified as pri- mary or generalized when clinical signs, symptoms, and supporting EEG changes indicate involvement of both hemispheres at onset. The clinical symptoms include unconsciousness and involve varying bilateral degrees of symmetric motor responses without evidence of local- ization to one hemisphere. These seizures are divided into six broad categories: tonic–clonic, absence seizures