Epilepsy and Seizures Workup
- Author: David Y Ko, MD; Chief Editor: Selim R Benbadis, MD more...
Two studies are often recommended after a seizure: neuroimaging evaluation (eg, brain magnetic resonance imaging [MRI], head computed tomography [CT] scanning) and electroencephalography (EEG). For neuroimaging, a CT scan is often obtained in the emergency department to exclude an obvious structural lesion, but an MRI is indicated if the patient continues to have seizures. In addition, lumbar puncture for cerebrospinal fluid (CSF) examination has a role in the patient with obtundation or in patients in whom meningitis, encephalitis, or subarachnoid hemorrhage is suspected.
Epileptic seizures have many causes, and some epileptic syndromes have specific histopathologic abnormalities. For more information, see the articles about specific epileptic syndromes listed in the Background section.
Historically, prolactin levels obtained shortly after a seizure (within 20 min) have been used to assess the etiology (epileptic or nonepileptic) of a spell. levels are typically elevated 3- or 4-fold, and elevations are more likely to occur with generalized tonic-clonic seizures than with other seizure types. However, not only has the considerable variability of prolactin levels precluded routine clinical use of such testing, but a baseline prolactin level is often obtained the next day at the same time as when the seizure first occurred, which makes the testing more cumbersome.
The American Academy of Neurology (AAN) recommends serum prolactin assays, measured in the appropriate clinical setting at 10-20 minutes after a suspected event as a useful adjunct for differentiating generalized tonic-clonic or complex partial seizure from psychogenic nonepileptic seizure in adults and older children.
The AAN notes, however, that prolactin assays do not distinguish epileptic seizures from syncope and have not been established in the evaluation of status epilepticus, repetitive seizures, and neonatal seizures. It should also be noted that wider availability of bedside video electroencephalography (EEG), the gold standard, has replaced prolactin testing for the evaluation of epileptic versus nonepileptic episodes.
Serum Studies of Anticonvulsant Agents
Judicious testing of serum levels of antiepileptic drugs (AEDs) may help to improve the care for patients with seizures and epilepsy. However, note that many new AEDs do not have readily obtainable or established levels. The following situations may be indications for obtaining serum AED levels:
Baseline measurements: After the seizures are controlled, the AED dose is then established, and the levels needed to achieve seizure-free effectiveness if there are expected changes in the levels, such as occurs with pregnancy, may be also be obtained
Toxicity and efficacy: The toxicity and efficacy of an AED is a clinical decision not based on levels per se but on how the patient is doing; an AED level may be helpful if the patient is at the recommended maximum dose but the serum level is not near that of the recommended maximum (thus, the clinician knows the drug dose can be increased, as there is room to achieve a higher AED level)
Medication noncompliance: Approximately 30% of patients miss at least 1 dose of their medication every month
Autoinduction or pharmacokinetic change, or patients who are unusual metabolizers of a medication
After an anticonvulsant has been used for several weeks, the baseline trough serum concentration slowly decreases because of hepatic autoinduction; this phenomenon is most often seen with carbamazepine, oxcarbazepine, and lamotrigine. Adding other medications with similar metabolic pathways may substantially change the clearance of some anticonvulsants.
The usual therapeutic range for an AED includes peak and trough levels measured in a group of adult patients. If a drug’s toxicity is under study, the peak level is desirable. In most circumstances, however, a trough level is the best indication of efficacy.
As with any medical test, serum concentrations of AEDs help clinical decision making, but the patient's individual response should be the main consideration. For example, a patient with juvenile myoclonic epilepsy (JME) might be seizure free with a valproic acid level of 30 mcg/mL, which is typically considered “subtherapeutic,” but if the patient is seizure free, the level is therapeutic. Therefore, clinical judgment regarding how well the patient is doing (ie, no seizures, no adverse effects) should prevail over a laboratory reading. Again, many new AEDs do not have a recommended level for testing, which is cost saving for that AED relative to many other AEDs in which serum levels are obtained reflexively (thus, adding to the cost of care).
A neuroimaging study, such as brain magnetic resonance imaging (MRI) or head computed tomography (CT) scanning, may show structural abnormalities that could be the cause of a seizure. If the patient has normal findings on neurologic examination and his or her condition (eg, cognitive, motor) returns to the usual baseline level between seizures, the preferred study is a brain MRI because of its resolution, which can depict subtle abnormalities.
Not every brain MRI study provides the same quality of information. Studies obtained with 3.0 Tesla (T) scanners may show better resolution than do conventional 1.5 T scanners or the "open-sided" scanners of 0.5 T. Brain MRIs obtained for epilepsy should have thin coronal sections via fast spin-echo (FSE) or fluid attenuation inversion recovery (FLAIR) sequences from the presumed region of epileptogenic zone; these are useful for assessing cortical lesions, which may be amenable to potentially curative surgery.
There are many new advances in MRI sequences to help in epilepsy presurgical evaluation. For more information, see Identification of Potential Epilepsy Surgery Candidates regarding imaging studies.
Electroencephalography and Video-Electroencephalography
Interictal epileptiform discharges or focal abnormalities on electroencephalography (EEG) strengthen the diagnosis of epileptic seizures and provide some help in determining the prognosis. Although the criterion standard for diagnosis and classification of epileptic seizures includes the interpretation of EEG, the clinical history remains the cornerstone for the diagnosis of epileptic seizures.
Video-EEG monitoring is the criterion standard for classifying the type of seizure or syndrome or for diagnosing pseudoseizures; that is, for establishing a definitive diagnosis of spells with impairment of consciousness. This study can be performed to rule out an epileptic etiology with a high degree of confidence if the patient has demonstrable impairment of consciousness during the spell in question. Video-EEG is also used to characterize the type of seizure and epileptic syndrome to optimize pharmacologic treatment and for presurgical workup.
However, video-EEG monitoring is an expensive and laborious study; therefore, monitoring all patients is impractical. Only those whose condition does not respond to treatment or in whom pseudoseizures are suspected should undergo video-EEG. Referral to an epilepsy center should be reserved for patients whose seizures are refractory to treatment. There is now a formal definition of patients who have medically refractory epilepsy: individuals who have tried 2 adequate doses of AED without a clinical response. Some frontal-lobe seizures are considered pseudoseizures for many years until appropriate diagnosis is made by means of video-EEG.
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