Identification of a TIA and its separation from focal epilepsy are aided by considering that most paroxysmal vascular disorders are characterized by loss of function that can be attributed to one area of the cortex such as paralysis, blindness, diplopia, or aphasia. If the ischemic attack is marked by an evolution of symptoms, they tend to develop more slowly than those of a seizure. The patient’s age and presence of vascular risk factors, evidence of disease of the heart and carotid arteries, and the lack of disorder of consciousness or amnesia may be supportive of the diagnosis of vascular disease. However, a “limb-shaking” TIA and convulsive phenomena at the outset of basilar artery occlusion may be nearly impossible to distinguish from epilepsy.
Regarding the distinction of seizures from odd disorders such as cataplexy, paroxysmal ataxia or choreoathetosis, transient global amnesia, it is sufficient to be aware of the diagnostic features for each of these conditions. REM sleep behavior disorder tend to occur later in the sleep cycle, as they require REM, whereas frontal epileptic seizures with violent motions or acts that might be mistaken for REM sleep behavior disorder, can occur at any time of the night and tend to be briefer than the sleep disorder. Drop attacks (falling to the ground without loss of consciousness as discussed in Chap. 6) remain an enigma. In most cases, it has not been possible to substantiate an association with circulatory disturbances of the vertebrobasilar system and seldom have we observed drop attacks to be an expression of atonic or myoclonic epilepsy.
Several laboratory studies are usually included in the initial diagnostic evaluation—complete blood count (CBC), blood chemistries, ECG, EEG, and imaging of the brain, preferably MRI. CT gives some information on major problems that may underlie epilepsy but MRI is superior in detecting the various structural causes of epilepsy. If blood is tested after the episode in question, elevation in creatine kinase (persistent for hours) and formerly, elevation of prolactin (for up to 10 min) may occur after an unwitnessed convulsive seizure but the test is not specific enough to be useful in general practice. Other forms of testing—for example, cardiac stress tests, Holter monitor, tilt-table testing, long-term cardiac rhythm monitors, and sleep studies—are sometimes indicated in order to exclude some of the nonepileptic disorders listed earlier. Some patients may need prolonged EEG monitoring, either in the hospital or with portable equipment at home. In all forms of epilepsy, prolonged EEG and video monitoring in a hospital unit may prove diagnostic.
(Table 15-4 and Fig. 15-5)
Having concluded that the neurologic disturbance under consideration is one of seizure, the next issue is to identify its type. Indeed, in most cases this determines the nature of treatment. Because there are so many seizure types, especially in childhood and adolescence, each one tending to predominate in a certain age period, a clinical advantage accrues to considering seizures from just this point of view. A broader approach includes consideration of the neurologic and EEG findings, the response to drugs, etiology, and prognosis.
Figure 15-5 displays the frequency of each seizure type and the main causes of seizures by age group. These data are assembled from various sources and are approximate, but they highlight several points of clinical importance.