Several complexities surround the evaluation of patients whose paroxysmal events may not represent true epileptic seizures. An increasing access by the public to medical information has produced a greater variety of nonepileptic attacks, as compared to heretofore when almost all such attacks resembled generalized tonic-clonic seizures. Now several features of true epileptic seizures, particularly those arising from the frontal lobe, are shared by psychogenic seizures, although the latter may last longer than the former. Additionally, true epileptic seizures may coexist with psychogenic seizures: Krumholz and Niedermeyer (95) have found that eighteen (37%) of their forty-four patients with psychogenic seizures had true epileptic seizures. However, the majority of patients with psychogenic seizures have no evidence of epilepsy.
Studies have found epileptiform discharges in 10 to 12% of patients with psychogenic seizures (96,97). Nonetheless, these percentages are higher than the 2 to 3% incidence found by Ajmone-Marsan and Zivin (9) in a patient population without a history of epilepsy. Nonspecific EEG abnormalities occur commonly among these patients, as found in about half of patients with psychogenic seizures and no epilepsy in one study (98).
Even with a full complement of electrodes and 24hour telemetered video-EEG, some EEG limitations in distinguishing epileptic from psychogenic seizures pertain: i) the spatial extent of some focal seizures may be insufficient to be detected by EEG, ii) seizures, particularly those arising from the frontal lobe, may occur in occult regions such as the inferior or mesial surfaces, and iii) movement or muscle artifact may obscure or complicate the display of ictal potentials.
True epileptic seizures are electrographically characterized by a morphological and/or frequency evolution of rhythmic waves or sequential epileptiform potentials followed by postictal attenuation (99). Such potentials should obey topological or physiological principles. In contrast, psychogenic seizures: i) often lack evidence of progression, ii) have potentials generated by attendant muscle, movement, or electrode artifacts that are topologically erratic, and iii) postictal delta or attenuation do not occur. Intraictally, alpha and other normal background potentials may be perceived among muscle, movement, and other artifacts.
Some laboratories apply an event-inducing stimulus such as a tuning fork. However, this may risk losing the patient's confidence in the medical team. Ambiguous or false positive responses may be evoked in patients without psychogenic seizures (100). Instead, clinical and EEG analysis together with MMPI-II data (101) usually establish the diagnosis without this measure.
Closely allied to psychogenic seizures is psy-chogenic unresponsiveness, identified by lack of any reaction to an afferent stimulus in the presence of a normal awake EEG. EEG helps to distinguish this phenomenon from absence and temporal lobe status epilepticus.
Was this article helpful?