Hypnotic recall: a positive criterion in the differential diagnosis between epileptic and pseudoepileptic seizures

Because the diagnosis of pseudoepileptic seizures (PESs) is mostly made by excluding epilepsy, availability of a positive criterion for PESs is of great importance. This study was aimed at the validation of a diagnostic technique that intends to provide in such a positive criterion.

In 17 patients with epileptic seizures (ESs) and 20 patients with PESs, a hypnotic procedure was performed by an investigator blind to other data to recover amnesia for the ictus. If recall was obtained, the experimental diagnosis PES was given; if not, ES was diagnosed. The experimental diagnoses were compared with the clinical, EEG-confirmed diagnoses. Hypnotizability was measured to determine the relation between the outcome of the test and hypnotizability of the patients.

Recall for the ictus was obtained in 17 patients. Each of these had a clinical diagnosis of PES. Seventeen patients with "no recall" had a clinical diagnosis of ES, and three patients had PESs. This result yields a specificity of 100% and a sensitivity of 85% for the recall technique. Hypnotizability was significantly higher in patients with PESs than in patients with ESs. In some "low hypnotizables," recall was obtained, and in some "high hypnotizables," no recall was obtained.

A positive recall test indicates PES. A sub-group of patients with PESs is characterized by a high level of hypnotizability. Hypnotizability is not crucial for outcome of the recall test. High hypnotic abilities are especially found in disorders in which it is supposed that "dissociation" is involved. It can be speculated that PES may be one of the dissociative phenomena.