Diagnosis of non-organic paralysis: Actual role of motor-evoked potentials

Introduction and Purpose. We wanted to assess the nature and temporal features of the diagnostic process, and particularly the role of motor-evoked potentials (MEPs), in 21 patients who ultimately had a diagnosis of non-organic paralysis. The detection of non-organic paralysis is still sometimes difficult. Previous authors [1,2] suggested that the finding of normal MEPs might be of special value. Methods. A retrospective study classified the patient clinical features, as well as the type, timing and results of the various (general, imaging, and psychiatric) investigations, MEPs and allied electrophysiological techniques included. These variables acted as dependent factors in a multivariate analysis of variance (MANOVA) model. The timing of the final diagnosis was the independent factor. Results. Diagnosis of non-organic paralysis proved to be a complex and time-consuming (on average 2 weeks) process . The only test whose timing showed a significant (MANOVA, F = 35.7, P<0.0001) statistical effect on the latency to diagnosis were the MEPs and allied neurophysiological studies. MEPs were invariably normal. On a cluster analysis, there were three significantly (P<0.05) different subgroups of patients with an early, intermediate, and late diagnosis respectively. MEPs were determined at the earliest in the "early diagnosis", and at the latest in the "late diagnosis" subgroup (P<0.05). In fact, there was a linear correlation between the timing of TMS and that of the diagnosis. Conclusions. We think that normal MEPs are actually crucial in the diagnosis of non-organic paralysis, if and when integrated by the appropriate (neurological, radiological, psychiatric) investigations. This is because MEPs may be normal in some patients with hemispheric ischemia [3]. Indeed, we document that an early transcranial/spinal stimulation was definitely associated with an early diagnosis. Then, if non-organic motor defects are suspected, one should obtain MEPs as soon as possible, but - of course - not omit the rest of the neurodiagnosis.