The brain controls how the body moves by sending electrical signals. Seizures occur when the normal signals from the brain are changed. These signals are caused by hyperactivity of an action potential, an impulse that moves from one cell to the next and passes along information. In the normal physiology of an action potential, thousands of cells that emit excitatory transmitters (acetylcholine and glutamate) and inhibitory transmitters (gaba aminobutyric acid [GABA]) converge on one cell. Excitatory neurotransmitters cause sodium to rush into a cell, and inhibitory neurotransmitters cause chloride to enter. Summation of the conversion of the excitatory and inhibitory neurons then takes place. If the excitatory neurons prevail, sodium enters the cell and potassium leaves the cell, resulting in an action potential. In this way, a signal is sent down the axon to the next cell (Armstrong et al., 2003).

A seizure occurs as a result of an imbalance characterized by more excitatory or less inhibitory activation in the central nervous system. Calcium causes an increase in excitatory neurotransmitter release, resulting in sodium entering the cell and potassium leaving. A long plateau of depolarization follows, causing numerous action potentials, then a period of hyperpolarization occurs as a result of GABA and chloride entering the cell. The hyperpolarization is soon replaced by depolarization, which increases in amplitude (Schaller & Ruegg, 2003). The cell then begins to fire repeatedly and produces sustained membrane depolarization, causing seizure activity.

Seizures usually start in one area of the brain, where the imbalance of cell activation occurs; this area is called the epileptogenic focus. If sufficient activation occurs to recruit surrounding neurons, the seizure propagates and activates other parts of the brain (Hickey, 2003). This results in a generalized seizure.

The preictal phase is the interval before the actual seizure. The patient is alert and oriented, without altered consciousness. The ictal phase is the initiation of seizure activity. The patient may experience activity consistent with the area of cerebral involvement. For example, if a tumor is located in the right frontal motor area of the brain, the patient will have arm or leg jerking on the left side. The postictal phase is the period after the seizure, during which the patient may be tired, confused, or disoriented (Fisher et. al., 2004).

Epilepsy is a condition marked by recurrent, unprovoked seizures caused by biochemical, anatomic, and physiologic changes (Jacobs & Shafer, 2000). Management of this condition usually requires daily medication to prevent seizures.

Many types of seizures have been described (Table 40-1) (Krouwer et al., 2000). The seizures commonly seen in patients with cancer or primary brain tumors are simple focal, complex partial, and generalized tonic-clonic seizures (Keles & Berger, 2000).

A simple focal seizure is localized, or generated from a specific part of the brain. It may involve a sensory function such as a funny smell, a strange feeling, visual changes, a sensation in the stomach, or a feeling of impending doom. A motor seizure may produce hand, leg, or mouth twitching. The patient does not lose consciousness. It may happen rarely or several times a day. A focal seizure can progress to the whole side of the body and become a generalized tonic-clonic seizure (Lovely, 2004).

A complex partial seizure occurs when the epileptic focus is in the temporal or frontal temporal lobe. The patient may have an initial feeling (aura or preictal phase) of an upset stomach or a funny smell. Consciousness is not lost, but the patient may lose track of the environment. Although the person may seem to be acting purposefully, he or she may have no control of behavior. For example, repetitive actions, known as automatisms, may happen, such as buttoning and unbuttoning a shirt, lip smacking, or hand wringing. These seizures may continue for only minutes or may last for days.

A generalized tonic-clonic seizure, informally known as a grand mal seizure, occurs if the chemical imbalance spreads into both sides of the brain. A patient may have an initial feeling that a seizure is imminent, such as a sensation or a focal seizure. Subsequently, a patient shows excessive movement of the arms and legs (tonic-clonic movements) with possible bowel and bladder incontinence (ictal phase). This type of seizure usually lasts about 1 to 2 minutes. After the seizure, during the postictal phase, the patient is quite tired and may want to sleep for hours.

Status epilepticus is a generalized tonic-clonic seizure that lasts longer than 5 minutes, or the occurrence of two or more seizures in succession without recovery. In rare cases, patients can experience continuous seizures, most often in the hospital setting. Detection requires electroencephalographic testing. Status epilepticus is a medical emergency (Victor et al., 2001). Left untreated, it may cause massive activation of the “stress” response of the sympathetic nervous system, resulting in elevated blood pressure and serum glucose. During prolonged seizures, the homeostatic mechanisms fail, and profound abnormalities result, including hypoxia, hypoglycemia, hypotension, and acidemia, with the potential to cause cortical nerve damage (Armstrong et al., 2003).

Seizures are known to originate from the disrupted normal tissue around the tumor rather than from the tumor itself. They also may be a result of treatment of a tumor (e.g., surgery, chemotherapy). Cranial radiation rarely causes seizures. However, focal radiation necrosis (i.e., dead tissue due to the radiation) can behave like an expanding intracerebral mass and cause seizures (Bromfield, 2004).

Seizures also may be caused by cerebrovascular disorders, such as hemorrhage or thrombosis. In addition, some medications may cause seizures, including certain chemotherapeutic drugs, antiemetics (phenothiazines), and allergy and cold products that contain diphenhydramine, which is thought to make patients with underlying neurologic damage more prone to having seizures. Metabolic abnormalities, such as hepatic failure, electrolyte abnormalities, hypoxia, and hyperglycemia, also are a cause of seizures (Armstrong et al., 2003).

Seizures induced by tumors usually are controlled with antiepileptic medication. In most cases, seizures do not cause death. Several episodes of status epilepticus may result in systemic and neurologic deterioration and a morbidity and mortality rate of 20% (Hickey, 2003). Adult onset epilepsy is associated with a poor quality of life because of mood changes and the adverse effects of antiepileptic medications. Coping measures help improve quality of life (Szalflarski et al., 2006).