Electrophysiological correlates of motor conversion disorder

Abstract

In patients with a functional (psychogenic) paresis, motor conduction tests are, by definition, normal. We investigated whether these patients exhibit an abnormal motor excitability. Four female patients with a functional paresis of the left upper extremity were studied using transcranial magnetic stimulation (TMS). We investigated motor thresholds, intracortical inhibition and intracortical facilitation at rest. Corticospinal excitability was evaluated by single pulse TMS during rest and during imagination of tonic index finger adductions. Data obtained from the affected first dorsal interosseous muscle were compared with the unaffected hand and with a healthy age-matched control group. Three patients demonstrated a flaccid paresis, one patient had a psychogenic dystonia. Motor thresholds, short interval intracortical inhibition and intracortical facilitation recorded from the affected side were normal. In healthy subjects, movement imagination produced an increase of corticospinal excitability. In the patients, motor imagery with the affected index finger resulted in a decrease of corticospinal excitability compared to rest, being significantly different from the unaffected side and from the control group. We suggest that suppression of corticospinal excitability during movement imagination is an electrophysiological correlate of the patients' inability to move voluntarily and provides some insight into the pathophysiology of this disorder.2008 Movement Disorder Society

Motor excitability during movement imagination and movement observation in psychogenic lower limb paresis

“…In another experiment, the authors described a specific slowing of motor initiation but not a general slowing involving motor execution [30]. Recent TMS studies with patients suffering from psychogenic upper limb paresis demonstrated that MI of finger movements with the affected limb induced a decrease of motor excitability, suggesting an inhibition of the motor system during that task [31,32]. The present study explored if a similar phenomenon can also be found in psychogenic lower limb paresis and if abnormalities occur to a comparable degree in MI and AO, respectively.…”

Functional Neuroanatomy and Neurophysiology of Functional Neurological Disorders (Conversion Disorder)

“…Liepert et al 32 showed that in response to motor imagery, patients with unilateral functional paralysis (N=5) or fixed dystonia (N=3) had a decrease in MEP of the affected hand by 37%, compared with rest with an increase in MEP by 63% of the unaffected side These findings were specific to MEPs because motor threshold, short intracortical inhibition, and intracortical facilitation were shown to be unremarkable among individuals with functional paralysis. 33,34 In healthy individuals, motor imagery commonly increases MEPs to a level comparable to that observed during executed movements. In a study by Liepert et al, 34 subjects…”

Multimodal Brain Analysis of Functional Neurological Disorders: A Functional Stroke Mimic Case Series

“…Interestingly, long-lasting functional paralysis has been associated with greater cortical thickness in motor areas, suggesting that functional brain abnormalities lead to structural changes when disease is sustained over time [4]. On the other hand, the increase in SICI (reflecting short-lasting postsynaptic inhibition mediated through the GABA A receptor) [7] further supports the hypothesis of a chronic dysfunction of self-referral regions, as precuneus and motor-related areas, mediated by an aberrant increase of the inhibitory GABAergic tone.…”

“…Furthermore, TMS has been used to test the integrity of corticospinal tracts, resting motor threshold, short-interval intracortical inhibition-facilitation (SICI-ICF), short-latency afferent inhibition (a parameter of sensorimotor integration), and LTP-like plasticity (to evaluate possible mechanisms of maladaptive plasticity) [6]. Limited TMS studies have reported a reduced cortical excitability in patients with FND during motor imagery of the affected limb [7]. In FND, no combined rs-fMRI/TMS studies are yet available.…”