Seizures and Epilepsy

Seizure disorders remain a critical neurological issue with an incidence of 39 per 100,000. Approximately, one-third of all cases prove intractable or treatment-resistant, despite the introduction of many new medication. Furthermore, many more cases of seizure disorder go undetected because EEG does not reliably capture seizure activity in the medial temporal lobe – a common source of partial complex seizures. SPECT can play a crucial role here. The figure shows a seizure foci in the right temporal lobe (blue arrows).

A seizure is an uncontrolled electrical burst in a group of neurons (a foci) within the brain. The extremely high activity levels of neurons during a seizure leads to very high rates of oxygen and glucose consumption, which induces increased blood flow. Seizures can remain localized (focal) or they can spread to involve the entire brain (generalized). During a generalized seizure, the person can show no symptoms (Absence), completely loss muscle control and tone (Atonic), demonstrate repetitive movements or subtle changes in behavior (Partial-Complex), or experience full-body alternating stiffening and jerking movements (Tonic-Clonic). Seizures can occur as part of epilepsy, characterized by recurrent seizures, or can result from acute disturbances in brain function, such as high fever, toxicity, alcohol withdrawal, and other transient conditions.

The symptoms of a seizure can vary widely, because different areas of the brain have different functions. Patients can experience both focal and generalized seizures at the same time. The symptoms can last anywhere from a few seconds to several minutes per episode. The longer a seizure lasts, the more dangerous it becomes to the patient. This is because blood flow in the brain may not be able to keep up with the oxygen and glucose demands of the seizing neurons. As a result, some neurons may die during a seizure. A prolonged seizure – also called status epilepticus – is a medical emergency.

Some patients experience warning signs or “auras” prior to the onset of a seizure. These can include:

  • sudden feeling of fear or anxiousness
  • nausea
  • dizziness
  • changes in vision
  • jerky movements of the arms and legs
  • “out of body” sensation
  • headache
  • repetitive bits of music or odd colours or visions

During generalized seizures, the patient will lose consciousness. Symptoms during a generalized seizure can include:

  • loss of consciousness
  • confusion
  • falling or collapsing
  • uncontrollable muscle spasms
  • drooling or frothing at the mouth
  • clenching of the teeth
  • biting of the tongue
  • grunting or unusual vocal sounds
  • loss of bladder or bowel control

However, seizures can be subtle with little overt movements or other signs. During focal or partial-complex seizures, a patient can be fully conscious. Symptoms during a focal or partial-complex seizure include:

  • confusion
  • headache
  • nausea
  • sudden mood changes
  • sudden feelings of fear or anxiousness
  • repetitive bits of music or odd colours or visions
  • dizziness
  •  “out of body” sensation
  • odd tastes or smells

Approximately 1.2-1.5% of people have epilepsy. An additional 5% of people may experience a single seizure in response to an acute disturbance of brain function, such as concussion, fever, toxicity, infection, chemical withdrawal, or high glucose levels.

The most common area of the brain from which seizures originate is the medial temporal cortex. Unfortunately, the medial temporal cortex is deep inside the brain and far from the surface of the scalp. Even the best electroencephalogram (EEG) equipment cannot detect electrical activity in the brain deeper than 1 cm. As a result, EEGs often miss the seizure foci located in the medial temporal lobe. This is particularly troublesome in the cases of patients with partial-complex seizures which by-and-large originate from the medial temporal lobe. These patients often experience derision and criticism from medical professional, because their seizure symptoms are labeled “psychiatric”.

Brain perfusion SPECT scans are an excellent tool for localizing seizure foci. Since SPECT scans visualize all parts of the brain, even the deeper parts, the seizure foci will not be missed. Localizing the seizure focus is a critical first step for surgical interventions in treatment-resistant epilepsy. Interictal (scan performed between seizures) scans can demonstrate areas of simmering seizure activity (increased perfusion). Comparing interictal to ictal (scan performed during a seizure) can clearly localize the seizure foci. An additional step of performing subtraction of the interictal scan data from the ictal scan data and overlying these data on an MRI is often used to localize a seizure foci for surgical or laser ablation. This is referred to as subtraction ictal SPECT co-registered to MRI (SISCOM). Perfusion SPECT performed during the seizure can localize the seizure focus in 71-93% of cases with a positive predictive value of 95%.

Localizing a seizure focus can also reframe a psychiatric patient as suffering from partial-complex seizures, rather than schizophrenia, bipolar disorder, or a personality disorder. For example, in the image below, an area of decreased perfusion is seen in the medial temporal lobe. This is an interictal (between seizures) image. During a partial-complex seizure, the patient experienced olfactory hallucinations, headache, and dizziness. The activity in these seizure foci would be high during the seizure. However, after the seizure, activity is markedly decreased as shown here.

An adolescent presenting with uncontrolled behavior, insomnia, impulsivity, and sexual promiscuity. The top row shows horizontal tomograms. The markedly increased activity of the frontal cortices is evident (red and white). The second row shows a 3-D map of brain activity. The widespread over-activity of the frontal cortices is better appreciated. The third row shows this patient’s data compared statistically to an age-matched normative database. Areas of 3 standard deviations above the mean appear as red. Areas of 4 SD above the mean appear as pink and areas of 5 SD above the mean appear as white. Clearly, this patient shows profound seizure-like overactivity in the frontal cortices. The scan and symptoms are consistent with bipolar mania. Note that mania and seizure activity share some common features.

Learn More