A seizure is a sudden surge of electrical activity in the brain that usually affects how a person feels or acts for a short time. Seizures are not a disease in themselves. Instead, they are a symptom of many different disorders that can affect the brain. Some seizures can hardly be noticed. Others are totally disabling.
A person who has had at least two seizures that were not caused by some known medical condition like alcohol withdrawal or extremely low blood sugar is classified has having epilepsy. The seizures in epilepsy may be related to a brain injury or a family tendency, but often the cause is completely unknown. The word "epilepsy" does not indicate anything about the cause of the person's seizures or how severe they are.
About half of the people who have one seizure without a clear cause will have another one, usually within a year. You are twice as likely to have another seizure if you have a known brain injury or other type of brain abnormality. If you do have two seizures, there's about an 80% chance that you'll have more.
If your first seizure occurred at the time of an injury or infection in the brain, you are more likely to develop epilepsy than if you had not had a seizure in that situation.
More than 1.5 million Americans have been treated for epilepsy in the last 5 years. That's 6.5 out of every 1,000 people.
Brain SPECT Imaging for the Detection of a Seizure focus.
A. Partial Complex Seizures/Temporal Lobe Epilepsy:
Seizures can be classified as either partial (focal) or generalized. Partial seizures originate in a given area of the brain and can be divided into simple (with no impairment of consciousness) and complex (with impairment of consciousness). Both simple and complex partial seizures may be preceded by sensations such as smells, tingling, or buzzing. About 10%-20% of patients with partial complex seizures have inadequate control on medical treatment. Patients unresponsive to anti-convulsant therapy may be surgical candidates which can render the patient seizure free. Scalp EEG often fails to accurately localize the seizure focus and although depth EEG is much more accurate, it is also extremely invasive and suffers from regional under sampling. CT and MRI have low sensitivity for seizure foci detection, 17% and 34% respectively.
1) SPECT Imaging During Ictal Phase.
Brain SPECT imaging can localize the seizure focus in 80% to 100% of patients during the ictal (during seizure) phase. Ictal SPECT studies have reported sensitivities between 81% to 93% (sensitivity 89%-97% for temporal lobe epilepsy and 73%-92% for neocortical epilepsy). The positive predictive value of SPECT imaging for localizing a unilateral seizure focus can be as high as 97%. Superimposition of SPECT images on MRI images can also aid in improved spatial localization.
2) SPECT During Inter-Ictal Phase.
Following a seizure, there is relatively rapid progression (generally within 20 minutes) to a lessened blood flow (hypoperfused) state which persists throughout the inter-ictal (seizure free) phase. SPECT studies performed during the inter-ictal phase will demonstrate an area of diminished activity at the seizure focus in up to 50% to 70% of patients. The area of lessened blood flow (hypoperfusion) is often much larger than the area of abnormality shown in the ictal phase.
Prognostically, patients with normal SPECT findings in the face of a localizing EEG are at a higher risk for a poor surgical outcome. However, it is imperative to note that a combination of a SPECT imaging finding of lessened blood flow (hypoperfusion) in the inter-ictal (seizure free) phase with more blood flow (hyperperfusion) in the same region on the SPECT ictal (during seizure) exam has absolute specificity of the seizure focus.
B). Frontal Lobe Epilepsy:
In the evaluation of frontal lobe epilepsy, SPECT imaging has demonstrated an increased blood flow (hyperperfused) seizure focus during the ictal (during seizure) phase in 90% of cases.
C). Status Epilepticus:
Status epilepticus is a condition in which seizures occur either continuously or so frequently that patients do not return to their baseline state between seizures. Although EEG can be very useful in the diagnosis, EEG abnormalities may be subtle or absent in these patients. In the evaluation of partial status epilepticus, ictal (during seizure) SPECT studies have demonstrated focal increased blood flow (hyperperfusion) in areas concordant with that suggested by EEG. Status epilepticus produces long term changes in regional brain blood flow that are not evident following a single seizure. As a result of this, persistent increased blood flow (hyperperfusion) may be observed by SPECT imaging for a prolonged period of time (possibly out to 6 days following the event).
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