There are two main seizure types: generalised and focal (or partial).
The type of seizure will influence decisions regarding neuroimaging. Determining seizure type is best done by close attention to patient and eyewitness descriptions of the event and the findings on an electroencephalography (EEG) done in close proximity to the seizure.
It is important to make the distinction between idiopathic generalised epilepsies (IGEs) and focal (localisation-related) epilepsies, as this affects further investigations, treatment choices, prognosis and counselling.8 An Australian study at a first seizure clinic found epileptogenic lesions in 17% of patients presenting with focal onset seizures.10
Patient history can often distinguish epileptic seizures from non-epileptic disorders by identifying the events directly preceding the seizure, associated conditions and details of the event, including possible triggers, duration and type of movements.11There can be difficulty in differentiating syncope from seizures based on patient self-reporting.
More than 50% of patients who present with a first seizure never have another. If patients do not have recurrence after 2 years, the risk falls to <10%. Patients with epileptic discharges on EEG or congenital neurological deficits have the highest recurrence rates (up to 90%).12
Additional investigations may be required after new onset seizure. EEG should be considered as part of the routine neurodiagnostic evaluation of adults presenting with an apparent unprovoked first seizure.7 Other testing should be performed based on clinical judgement.
An MRI is not always required for a patient with new onset seizure. Idiopathic generalised epilepsy is not associated with an increased prevalence of brain lesions; therefore, if this is confidently diagnosed, the patient does not require imaging.8However, as neuroimaging is recommended in most situations of new onset seizure,11,13 many patients who are later diagnosed with idiopathic generalised epilepsy will have neuroimaging after their first seizure.
Neuroimaging (preferably MRI) is recommended after a first unprovoked seizure for all adults with risk factors.11,14
Note that seizures are a feature of some brain tumours and may precede tumour diagnosis by years.15