With an incidence of 0.5% in the population, selectivity in investigation is often necessary. CT scanning is not always routinely available.
The concern of the clinician is that epilepsy may be symptomatic of a treatable cerebral lesion. Investigations serve to define a cause and to aid diagnosis in difficult cases.
Biochemistry (electrolytes, urea and calcium)
CT or MRI should always be performed when seizures are:
- late in onset
- partial in type
- refractory in nature (to drug treatment)
- associated with abnormal clinical signs or when epilepsy presents as status epilepticus
In doubtful cases the diagnosis should be deferred rather than labelling the patient 'epileptic'.
Specialised neurophysiological investigations
Indicated if attacks of unconsciousness are frequent or persistent and the diagnosis remains unclear.
Sleep deprived electroencephalography (EEG). 'Activated' EEG recording with procyclidine or other drugs. Telemetric EEG recording over 24—48 hours often combined with video recording of the patients (split screen display).
These investigations may reveal 'diagnostic' epileptic discharges or confirm non-epileptiform seizures.
These are reserved for cases of intractable epilepsy where surgery is considered. Telemetric, sphenoidal, foramen ovale and intraoperative EEG recording. Magnetic resonance imaging may display low grade gliomas, hamartomas, neuronal migration disorders or mesial temporal sclerosis, lesions often missed on CT scanning. Positron emission tomography (PET) or single photon emission computed tomography (SPECT) localise functional changes in cerebral blood flow and metabolism.
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