Porth's Essentials of Pathophysiology, 4e

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Disorders of Brain Function

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legs and arms extended. If the person is standing, they may fall to the ground. Clonic Seizures. Clonic seizures, which are similar to those seen during the clonic phase of a tonic-clonic sei- zure, are characterized by repetitive rhythmic muscular contractions that are bilateral and symmetric, and are accompanied by hyperventilation. Atonic Seizures. In atonic seizures, there is a sudden, split-second loss of muscle tone leading to slackening of the jaw, drooping of the limbs, and falling to the ground. These seizures also are known as “drop attacks.” Diagnosis andTreatment The diagnosis of seizure disorders is based on a thor- ough history and neurologic examination, including a full description of the seizure. 7,56,60,61 The physical examination and laboratory studies help exclude any metabolic disorder (e.g., hyponatremia) that could pre- cipitate seizures. Magnetic resonance imaging scans are used to identify structural defects such as temporal lobe sclerosis or underlying congenital malformations caus- ing the seizure. One of the most useful diagnostic tests is the EEG, which is used to record changes in the brain’s electrical activity. It is used to support the clinical diag- nosis of epilepsy, to provide a guide for prognosis, and to assist in classifying the seizure disorder. The first rules of treatment are to protect the per- son from injury during a seizure, preserve brain func- tion by aborting or preventing seizure activity, and treat any underlying disease. People with epilepsy should be advised to avoid situations that could be dangerous or life-threatening if seizures occur. The management of seizure disorders focuses on treatment of the underly- ing conditions that cause or contribute to the seizures, avoidance of precipitating factors, suppression of recur- rent seizures by prophylactic therapy with antiepileptic medications, surgery or neurostimulation, and address- ing psychological and social issues. 7,56,60 Antiepileptic DrugTherapy Antiepileptic drug therapy is the mainstay of treatment for most persons with epilepsy. It is individualized for each patient based on the different types and causes of seizures as well as medication efficacy and side effects. Antiepileptic drugs act mainly by suppressing repeti- tive firing of isolated neurons that act as epileptogenic foci for seizure activity or by inhibiting the transmis- sion of electrical impulses involved in seizure activity. 62 Because of their selective mechanisms of action, different drugs are used to treat the different types of seizures. For example, ethosuximide, which suppresses the brain wave activity associated with lapses of consciousness, is used in the treatment of absence seizures, but is not effective for tonic-clonic seizures that progress from focal seizures. More than 20 drugs are available for the treatment of epilepsy. 64 This group includes 12 new antiepileptic drugs that have been approved for use in the United

States in the past several decades. 63 The goal of pharma- cologic treatment is to bring the seizures under control with the least possible disruption in lifestyle and mini- mum of side effects from the medication. Whenever possible, a single drug should be used. Monotherapy eliminates drug interactions and additive side effects. Determining the proper dose of the anticonvulsant drug is often a long and tedious process, which can be very frustrating for the person with epilepsy. 64 Blood tests are often used to determine that the blood con- centration is within the therapeutic range. Consistency in taking the medication is essential. Antiepileptic drug use never should be discontinued abruptly. Special consideration is needed when a person taking an anti- epileptic medication becomes ill and must take addi- tional medications. Some drugs act synergistically, and others interfere with the actions of other medications. This situation needs to be carefully monitored to avoid overmedication or interference with successful seizure control. Women of child-bearing age require special consider- ation concerning fertility, contraception, and pregnancy. Many of the drugs interact with oral contraceptives; some affect hormone function or decrease fertility. All such women should be advised to take folic acid sup- plementation. For women with epilepsy who become pregnant, antiseizure drugs increase the risk for con- genital abnormalities and other perinatal complications. Carbamazepine, phenytoin, phenobarbital, primidone, and valproic acid can interfere with vitamin D metabo- lism and predispose to osteoporosis. Surgical and NeurostimulationTherapy Surgical treatment may be an option for persons with epilepsy who are refractory to drug treatment. 7,60 With the use of modern neuroimaging and surgical tech- niques, a single epileptogenic lesion can often be identi- fied and removed without leaving a neurologic deficit. The most common surgery consists of removal of the amygdala and an anterior part of the hippocampus and entorhinal cortex, as well as a small part of the tempo- ral pole, leaving the lateral temporal neocortex intact. Another surgical procedure involves partial removal of the corpus callosum to prevent spread of a unilateral seizure to a generalized seizure. Neurostimulation, with the development of a variety of different devices and targets of stimulation, is a rap- idly evolving field in the treatment of epilepsy. 65 Methods of external (noninvasive) trigeminal stimulation have been developed and are currently being evaluated. These methods seem promising not only as therapy, but also as a useful predictor of success with other forms of stimu- lation therapy. A subcutaneous implantable device is also being evaluated.

Generalized Convulsive Status Epilepticus

Seizures that do not stop spontaneously or occur in suc- cession without recovery are called status epilepticus.