Aim: To investigate the efficacy of transcranial magnetic stimulation (TMS) with a cue signal for the objective diagnosis of palsy of conversion disorder (CD).
Methods: Ten patients with palsy of CD, nine with amyotrophic lateral sclerosis (ALS), and eight control subjects were examined. Motor evoked potential (MEP) was recorded from the abductor digiti minimi muscle under three conditions: at rest, during tonic contraction, and with an audio cue signal. In the cue signal paradigm, subjects were asked to perform ramp-and-hold contraction in response to a cue signal.
Results: MEP size increased in the cue signal paradigm in both controls and patients with ALS, but was not obvious in some CD patients. This was likely due to variance among trials in the cue signal paradigm in each CD patient. The coefficients of variance (CV) among trials in the cue signal paradigm were 15 +/- 4.3 in controls, 25 +/- 11 in ALS, and 70 +/- 40 in CD.
Conclusions: CV of MEP size with cue signal was larger in CD than in controls (P < 0.005) and in ALS patients (P < 0.01). The size variance among MEP trials with the cue signal is a supportive parameter for the diagnosis of CD.