Partial seizures are due to electrical discharges, which begin in a localized region of the cerebral cortex; the discharge may remain localized or may spread to involve nearby cortical regions or the entire cortex. Focal seizures are generally thought to be secondary seizures, their occurrence implying a localized structural lesion of the brain.
In simple partial focal seizures, the seizure remains localized, and consciousness and mentation are not affected. It is possible to deduce the likely location of the initial cortical discharge from the clinical features at the onset of the attack. Unilateral tonic or clonic movements, often limited to one extremity, suggest a focus in the motor cortex, while tonic deviation of the head and eyes suggests a frontal lobe focus. Sensory hallucinations (e.g., paresthesias or numbness) suggest a discharge in the sensory cortex. Visual symptoms, especially flashing lights or distortions of vision, suggest an occipital focus. Bizarre olfactory or gustatory hallucinations suggest a focus in the medial temporal lobe. Such sensory phenomena, known as auras, are often the initial symptoms of attacks that then become more widespread, and that are termed secondary generalization.
Complex partial seizures are focal seizures in which consciousness and/or mentation are affected. They are often caused by a focal discharge originating in the temporal lobe and are sometimes referred to as temporal lobe seizures. Because of their alterations of thinking and behavior, they are occasionally called psychomotor seizures. As such seizures may originate from brain regions other than the temporal lobes, and to avoid any confusion with psychiatric illness, the term complex partial seizures is preferred. Often thought to be rare, they are, in fact, quite common.
Because of their frequently bizarre symptoms, complex partial seizures are commonly misdiagnosed as psychiatric problems. Their symptoms may include automatisms, visceral symptoms, hallucinations, memory disturbances, distorted perception, and affective disorders. Automatisms are typically simple, repetitive, purposeless movements such as lip smacking, fiddling with clothing or buttons, or repeating short phrases. More complex behaviors may occur, but well-organized, purposeful activity is unlikely. Visceral symptoms often consist of a sensation of "butterflys" rising up from the epigastrium. Hallucinations may be olfactory, gustatory, visual, or auditory. There may be complex distortions of visual perception, time, and memory. Affective symptoms may include intense sensations of fear, paranoia, depression, or, rarely, elation or ecstasy.
As noted, a focal seizure discharge may spread to involve both hemispheres, mimicking a typical generalized seizure. This is termed secondary generalization. For the purpose of classification, diagnosis, and treatment, such attacks are regarded as focal seizures. In some patients, the discharge may spread so rapidly that no focal symptoms are evident, and the correct diagnosis may depend on demonstration of the focal discharge on an EEG recording.
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