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Focal seizures (also called partial seizures and localized seizures) are seizures which affect initially only one hemisphere of the brain. The brain is divided into two hemispheres, each consisting of four lobes – the frontal, temporal, parietal and occipital lobes. In partial seizures the seizure is generated in and affects just one part of the brain – the whole hemisphere or part of a lobe. Symptoms will vary according to where the seizure occurs. In the frontal lobe symptoms may include a wave-like sensation in the head; in the temporal lobe, a feeling of déjà vu; in the parietal lobe, a numbness or tingling; and in the occipital lobe, visual disturbance or hallucination.
Focal seizures are split into two main categories; simple focal seizures and complex focal seizures.
In simple focal seizures a small part of one of the lobes may be affected and the person remains conscious. This will often be a precursor to a larger seizure such as a complex partial seizure. When this is the case, the simple partial seizure is usually called an aura.
A complex focal seizure affects a larger part of the hemisphere than a simple partial seizure and the person may lose consciousness.
If a focal seizure spreads from one hemisphere to the other side of the brain, this will give rise to a secondarily generalised seizure. The person will become unconscious and may well have a tonic clonic seizure. When people have multiple focal seizures they generally have a condition known as temporal lobe epilepsy.
Simple focal seizure
Simple focal seizures are seizures which affect only a small region of the brain, often the temporal lobes or hippocampi. People who have simple partial seizures retain consciousness. Simple partial seizures often precede larger seizures, where the abnormal electrical activity spreads to a larger area of (or all of) the brain, usually resulting in a complex partial seizure or a tonic-clonic seizure. In this case they are often known as an aura.
Simple partial seizures are a very subjective experience, and the symptoms of a simple partial seizure vary greatly between people. This is due to the varying locations of the brain the seizures originate in e.g.: Rolandic. A simple partial seizure may go unnoticed by others or shrugged off by the sufferer as merely a "funny turn." Simple partial seizures usually start suddenly and are very brief, typically lasting 60 to 120 seconds.
While awake some common symptoms of simple partial seizures are:
- preserved consciousness
- sudden and inexplicable feelings of fear, anger, sadness, happiness or nausea
- sensations of falling or movement
- experiencing of unusual feelings or sensations
- altered sense of hearing, smelling, tasting, seeing, and tactile perception (sensory illusions or hallucinations), or feeling as though the environment is not real (derealization) or dissociation from the environment or self (depersonalization)
- a sense of spatial distortion—things close by may appear to be at a distance
- déjà vu (familiarity) or jamais vu (unfamiliarity)
- laboured speech or inability to speak at all
- usually the event is remembered in detail
When the seizure occurs during sleep, the person will often become semi-conscious and act out a dream they were having while engaging with the real environment as normal. Objects and people usually appear normal or only slightly distorted to them, and will be able to communicate with them on an otherwise normal level. However, since the person is still acting in the dream-like state from which they woke, they will assimilate any hallucinations or delusions into their communication, often speaking to a hallucinatory person or speaking of events or thoughts normally pertaining to the dream they were having or other hallucination.
While asleep symptoms include:
- onset usually in REM sleep
- dream like state
- appearance of full consciousness
- hallucinations or delusions
- behavior or visions typical in dreams
- ability to engage with the environment and other people as in full consciousness, though often behaving abnormally, erratically, or failing to be coherent
- complete amnesia or assimilating the memory as though it was a normal dream on regaining full consciousness
Although hallucinations may occur during simple partial seizures they are differentiated from psychotic symptoms by the fact that the person is usually aware that the hallucinations are not real.
Jacksonian march or Jacksonian seizure is a phenomenon where a simple partial seizure spreads from the distal part of the limb toward the ipsilateral face (on same side of body). They involve a progression of the location of the seizure in the brain, which leads to a "march" of the motor presentation of symptoms.
Jacksonian seizures are initiated with abnormal electrical activity within the primary motor cortex. They are unique in that they travel through the primary motor cortex in succession, affecting the corresponding muscles, often beginning with the fingers. This is felt as a tingling sensation, or a feeling of waves through the fingers when touched together. It then affects the hand and moves on to more proximal areas on the same side of body. Symptoms often associated with a Jacksonian seizure are sudden head and eye movements, tingling, numbness, smacking of the lips, and sudden muscle contractions. Most of the time any one of these actions can be seen as normal movements, without being associated with the seizure occurring. They occur at no particular moment and last only briefly. They may result in secondary generalized seizure involving both hemispheres. They can also start at the feet, manifesting as tingling or pins and needles, and there are painful cramps in the foot muscles, due to the signals from the brain. Because it is a partial seizure, the postictal state is of normal consciousness.
These seizures are named after their discoverer, John Hughlings Jackson, an English neurologist, whose studies led to the discovery of the seizures' initiation point (in the primary motor cortex) in 1863.
Complex focal seizure
A complex focal seizure is an epileptic seizure that is associated with unilateral cerebral hemisphere involvement and causes impairment of awareness or responsiveness, i.e. alteration of consciousness.
Complex focal seizures are often preceded by a seizure aura. The seizure aura is a simple partial seizure. The aura may manifest itself as a feeling of déjà vu, jamais vu, fear, euphoria or depersonalization.[better source needed] The seizure aura might also occur as a visual disturbance, such as tunnel vision or a change in the perceived size of objects. Once consciousness is impaired, the person may display automatisms such as lip smacking, chewing or swallowing. There may also be loss of memory (amnesia) surrounding the seizural event. The person may still be able to perform routine tasks such as walking, although such movements are not purposeful or planned. Witnesses may not recognize that anything is wrong.
Complex partial seizures might arise from any lobe of the brain. Complex partial seizures most commonly arise from the mesial temporal lobe, particularly the amygdala, hippocampus, and neocortical regions. A common associated brain abnormality is mesial temporal sclerosis. Mesial temporal sclerosis is a specific pattern of hippocampal neuronal loss accompanied by hippocampal gliosis and atrophy. Complex partial seizures occur when excessive and synchronous electrical brain activity causes impaired awareness and responsiveness. The abnormal electrical activity might spread to the rest of the brain and cause a secondary generalized tonic–clonic seizure.
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