Diagnosis of psychogenic paralysis: The role of motor evoked potentials

Abstract

Background In the nineties, there has been evidence that motor evoked potential (MEP) studies might improve the diagnosis of psychogenic paralysis. Objective To review a series of patients (1986–1999) who finally had a diagnosis of psychogenic paralysis at our Institutions. To detect if, over that period, the time taken to make the diagnosis had changed, and, if so, this had any relationship to the diagnostic tests used or to other variables. Methods We selected a patient sample (n=21) seen by the same team of neurologists, whose diagnostic criteria were homogeneously based on the DSM IV, and who were studied with MEPs. We analysed their clinical features, the type and timing of the investigations done, and the time taken to make the diagnosis. These variables acted as the dependent factors in a Multivariate Analysis of Variance (MANOVA) model, in which the year of observation was the fixed factor. Results The diagnosis was 50 % earlier in the period 1993 to 1999 (10 patients) than in the period 1986–1992 (11 patients) (F = 28.3, p < 0.0001). The only associated change was an earlier MEP study (F=18.4, p < 0.0001), which invariably showed normal findings. Conclusion MEP studies contributed to speed up the diagnosis of psychogenic paralysis. Possibly, normal MEPs rendered the neurologist confident about the physiological integrity of motor fibers in the corticospinal tract, anterior roots and plexuses. Such integrity, if nerve trunks and muscles are intact, and in the appropriate diagnostic context, implies a psychogenic cause for paralysis.