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Partial seizures (also called focal seizures and localized seizures) are seizures which affect only a part of the brain at onset. 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.
Partial seizures are split into two main categories; simple partial seizures and complex partial seizures. A new classification system for partial seizures has been described in the 18th Edition of Harrison's Principles of Internal Medicine (released July 2011). The new classification splits partial seizures into "partial seizures with dyscognitive features" and "partial seizures without dyscognitive features".
In simple partial 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 partial seizure affects a larger part of the hemisphere than a simple partial seizure and the person may lose consciousness.
If a partial 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.
Partial seizures are common in temporal lobe epilepsy.