Application of signal detection theory to verbal memory testing to distinguish patients with psychogenic nonepileptic seizures from patients with epileptic seizures Kelly A. McNally a,1 , Bruce K. Schefft a,b, * , Jerzy P. Szaflarski b , Steven R. Howe a , Hwa-Shain Yeh c , Michael D. Privitera b a Department of Psychology, University of Cincinnati, Cincinnati, OH, USA b Department of Neurology, University of Cincinnati Medical Center, Cincinnati, OH, USA c Department of Neurosurgery, University of Cincinnati Medical Center, Cincinnati, OH, USA article info Article history: Received 20 May 2008 Revised 11 January 2009 Accepted 17 January 2009 Available online 7 February 2009 Keywords: Temporal lobe epilepsy Recognition memory Psychogenic nonepileptic seizures Signal detection theory Response bias Conversion disorder abstract Distinguishing psychogenic nonepileptic seizures (PNES) from epileptic seizures (ES) is a difficult task that is often aided by neuropsychological evaluation. In the present study, signal detection theory (SDT) was used to examine differences between these groups in neuropsychological performance on the Wechsler Memory Scale, Third Edition, Word List Test (WMS-III WLT). The raw WMS-III WLT scores on this task failed to discriminate the two groups; however, with the use of SDT, patients with PNES were found to have a negative response bias and increased memory sensitivity as compared with patients with ES. When patients with left (LTLE) and right (RTLE) temporal lobe epilepsy were compared, the patients with LTLE demonstrated decreased memory sensitivity but a similar response bias as compared with the patients with RTLE. Memory impairment in patients with PNES may be related to faulty decision-making strategies, rather than true memory impairment, whereas memory performance differences between the LTLE and RTLE groups are likely related to actual differences in memory abilities. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction A common and often difficult task in the evaluation of seizure disorders is the differential diagnosis of epileptic seizures (ES) and psychogenic nonepileptic seizures (PNES). PNES refers to a psycho- logically induced behavior pattern that mimics ES, but is not associ- ated with any EEG changes. It is generally thought that in most patients PNES constitute a type of conversion disorder in which psy- chological distress is manifested somatically, in the form of seizure- like behaviors [1]. PNES is a debilitating disorder, often resulting in poor quality of life and significant mood disturbances [2]. Although prevalence estimates vary widely, it has been reported that up to 50% of patients referred to epilepsy monitoring units may have seizures that are psychogenic rather than organic in nature [3]. The incidence of PNES has been reported to be 3/100,000 [2]. PNES events often are difficult to distinguish from ES solely on the basis of clinical presentation [4]. Thus, more sophisticated methods of differential diagnosis are required. The current gold standard in the differential diagnosis of PNES versus ES is pro- longed video/EEG monitoring (PVEM) that, in patients with PNES, is either normal or unchanged from baseline. In patients with ES, PVEM is associated with paroxysmal discharge(s) accompanying seizure behaviors. Although PVEM provides accurate diagnosis, this procedure is complex, costly, and not available at all medical centers [5]. Furthermore, in the absence of EEG abnormalities dur- ing PVEM, the possibility of ES cannot be ruled out entirely. For example, cases of frontal or parietal lobe epilepsy may be particu- larly difficult to detect on scalp EEGs [6]. Thus, other less expensive and labor-intensive methods of differential diagnosis, such as neu- ropsychological testing, need to be investigated. It is generally thought that, because of the organic nature of the disorder, patients with ES show greater cognitive dysfunction on neuropsy- chological assessment as compared with patients with PNES. How- ever, the results of available studies have been mixed, with some reporting no differences between PNES and ES groups on neuro- psychology testing results (e.g., [7,8]), some reporting more impairment in the ES group (e.g., [9]), and some reporting greater impairment on certain measures in patients with PNES (e.g., [10]). Cragar et al. [5] conducted a comprehensive review of studies investigating the neuropsychological performance of patients with 1525-5050/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.yebeh.2009.01.012 * Corresponding author. Address: Department of Psychology, University of Cincinnati, PO Box 210376, Cincinnati, OH 45221-0376, USA. E-mail address: scheffbk@ucmail.uc.edu (B.K. Schefft). 1 This work was part of the first author’s Master’s Thesis, chaired by the second author, in the Department of Psychology, University of Cincinnati. Epilepsy & Behavior 14 (2009) 597–603 Contents lists available at ScienceDirect Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh