Approach Considerations
Metabolic screening for uremia, hypoglycemia, drug intoxications, and electrolyte disorders should be conducted for patients with first seizure who present to the emergency department. [36] Perform other laboratory investigations as indicated for specific clinical situations.
Neuroimaging should be performed, because discovery of an epileptogenic lesion can have an impact on the diagnosis, prognosis, and treatment of new-onset seizures. Chadwick and Smith concluded that plausible arguments may be made for obtaining routine early computed tomography (CT) scanning and reserving magnetic resonance imaging (MRI) for patients with epilepsy whose seizures are not controlled by antiepileptic drugs. [37]
Neuroimaging
Magnetic resonance imaging (MRI) improves diagnostic accuracy. Using clinical and electroencephalographic (EEG) data alone, King et al were able to identify 23% of patients as having primary generalized epilepsy, 54% as having partial epilepsy, and 23% as having unclassified seizures. [28] Using clinical, EEG, and MRI data, the investigators were able to determine that 23% of patients had primary generalized epilepsy, 58% had partial epilepsy, and 19% had unclassified seizures. [28]
Computed tomography (CT) scanning may miss surgically remedial brain lesions that would otherwise be detected by MRI. King et al found that CT scanning detected only 12 of the 28 brain lesions that were detected by MRI; 7 of the missed lesions were brain tumors. [28]
Neuroimaging is unlikely to detect brain lesions in patients with clinical and EEG features of idiopathic generalized epilepsy or benign rolandic epilepsy. King et al found that MRI did not detect any brain lesions in 49 patients with clinical and EEG features of idiopathic generalized epilepsy or in 11 patients with benign rolandic epilepsy. [28]
Electroencephalography
Electroencephalography (EEG) should be performed within 24 hours of the seizure, because this study is significantly more sensitive when obtained during that period (see the following images). [25] If the routine EEG findings are normal, a sleep-deprived EEG should be performed. Standard EEG detects epileptiform discharges in 29% of patients; however, standard EEG combined with sleep-deprived EEG shows epileptiform discharges in 48% of patients. [18]
An electroencephalogram (EEG) recording of a temporal lobe seizure. The ictal EEG pattern is shown in the rectangular areas.
An electroencephalogram (EEG) recording from a patient with primary generalized epilepsy. A burst of bilateral spike and wave discharge is shown in the rectangular area.
An electroencephalogram (EEG) recording of a seizure from a subdural array in a patient evaluated for epilepsy surgery. The subdural electrodes record from the left anterior temporal (LAT), left middle temporal (LMT), and left posterior temporal (LPT) regions. The EEG seizure pattern is seen best in bipolar EEG channels LAT 3-4 and LMT 3-4 (rectangular areas).
EEG significantly improves diagnostic accuracy in patients with a first seizure. Using clinical data alone, King et al were able to determine that 8% of patients had primary generalized epilepsy, 39% had partial epilepsy, and 53% had unclassified seizures. [25] When using clinical and EEG data together, the investigators were able to determine that 23% of patients had primary generalized epilepsy, 53% had partial epilepsy, and 23% had unclassified seizures. [25]
Schreiner and Pohlman-Eden studied the value of an EEG taken within 48 hours of the first seizure in an adult. [38] They found that 38% of patients without seizure recurrence had normal EEGs, while only 10.2% of patients with seizure recurrence had normal EEGs. Focal epileptiform activities were found significantly more frequently (26.5% vs 13%) in patients with seizure recurrence than in patients without seizure recurrence.
Unfortunately, although EEG can be helpful, it is often harmful, because normal EEGs are frequently overread as epileptiform, leading to the misdiagnosis of seizures. [33, 39] The tendency to overread normal EEGs is common and has numerous causes. [40] The most common reason for misdiagnosis is that the history is not suggestive of seizures, but the entire diagnosis is essentially based on the EEG.
Insertable Loop Recorder
Whenever cardiovascular causes are considered as the cause of a patient's spells but cannot be proven with conventional investigations, the use of the insertable loop recorder should be considered. Simpson et al described a case in which the placement of an insertable loop recorder, an important new tool in the diagnostic evaluation of patients with syncope, led to an unexpected diagnosis of a seizure. [41]
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An electroencephalogram (EEG) recording of a temporal lobe seizure. The ictal EEG pattern is shown in the rectangular areas.
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An electroencephalogram (EEG) recording from a patient with primary generalized epilepsy. A burst of bilateral spike and wave discharge is shown in the rectangular area.
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An electroencephalogram (EEG) recording of a seizure from a subdural array in a patient evaluated for epilepsy surgery. The subdural electrodes record from the left anterior temporal (LAT), left middle temporal (LMT), and left posterior temporal (LPT) regions. The EEG seizure pattern is seen best in bipolar EEG channels LAT 3-4 and LMT 3-4 (rectangular areas).
