Summary: Purpose:To develop an objective classification of psychogenic nonepileptic seizures (NES) based on cluster analysis of clinical seizure semiology.Methods: We studied the clinical seizure semiology in 27 patients with psychogenic NES documented by prolonged video-EEG monitoring. We analyzed the following clinical symptoms: clonic and hypermotor movements as well as trembling of the upper and/or lower extremities, pelvic thrusting, head movements, tonic posturing backward of the head, and falling. We used cluster analysis to identify symptoms occurring together in a systematic way and thus tried to achieve a clinical classification of psychogenic NES.Results: We could identify three symptom clusters. Cluster 1 was characterized by clonic and hypermotor movements of the extremities, pelvic thrusting, head movements, and tonic posturing of the head, and therefore was named "psychogenic motor seizures." Cluster 2 comprised trembling of the upper and lower extremities and was termed "psychogenic minor motor or trembling seizures." Cluster 3 consisted of falling to the floor as the only symptom and was referred to as "psychogenic atonic seizures."Conclusions: Our study represents the first study to analyze the clinical semiology of psychogenic NES by cluster analysis, which should be useful for an objective classification of psychogenic NES. This classification should allow both a better characterization of psychogenic NES and an easier differential diagnosis against specific epileptic seizures. Key Words: Psychogenic nonepileptic seizures-Classification-Differential diagnosis.Psychogenic nonepileptic seizures (NES) represent an important differential diagnosis of difficult-to-treat epileptic seizures (1). In a recent population-based study from Iceland, the incidence of NES was 1.4 in 100,000 persons per years of observation with a maximum agespecific incidence between 15 and 24 years and a strong female preponderance (2). In several clinical series, the relative frequency of psychogenic NES ranged from 5 to 20% in outpatient epilepsy populations (3) and from 10 to 40% in patients studied in epilepsy centers (43). The correct identification of psychogenic NES is important to avoid unnecessary prolonged intake of antiepileptic drugs (AEDs), to offer the patient the appropriate treatment including psychotherapy, and finally to prevent potential iatrogenic hazards including ventilatory assistance for pseudostatus epilepticus (6,7).Although correct diagnosis of psychogenic NES often is very difficult (9). In these instances, prolonged video-EEG monitoring with the simultaneous recording of a typical ictal event and the ongoing EEG is the only method that facilitates the differentiation of psychogenic NES from epileptic seizures (10). Several video-EEG monitoring studies identified clinical features characteristic of psychogenic NES, including a gradual onset and a prolonged duration of the attacks (8), closed eyes during a paroxysmal event (1 l), periictal headache (1 2), periictal pseudosleep (13), and ictal wee...

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