Excitability of the motor cortex during motor imagery and observation in patients with Complex Regional Pain Syndrome (CRPS) and tonic dystonia

The etiology of tonic dystonia in Complex Regional Pain Syndrome (CRPS) is
unknown. There are some indications that it is a functional movement disorder.
This means that their is no known underlying organic pathology (eg stroke).
Clinically this is reflected in signs that are not present in all situations.

A hypothesis for the etiology of conversion disorders is frontal inhibition.
This means that the brains themselves inhibit movement programmes resulting in
paralysis. The assumption is that this is caused by a traumatic experience in
the past. In new and threatening situations the brain overreacts which causes
the movement disorder.
It is unknown whether movement disorders such as tonic dystonia (with increased
instead of decreased muscle tone is present) are due to a similar mechanism.
Although there is no evidence, this is often assumed for CRPS patients with
dystonia and therefor these patients are often portrayed as conversion
patients.

to find evidence for frontal inhibition during planning of explicit movements
just as seen in patients with conversion disorders.

Two situations.

1: Participants are asked to watch a video that shows a moving hand (opening
and closing of a hand) in first persons perspective. (as if it is their own
hand). It is known that the spectator (unconsciously) replicates the movement
in the brain. He or she is told not to move their own hand. While watching the
videos, a TMS signal is induced over the motor cortex. The evoked Motor Evoked
Potentials (MEP) are measured in muscles of the hand tested. Cortical
inhibition will be reduced by watching the movie (MEPs are higher in comparison
to rest) which means the cortex is active. This is expected in all groups.

2: The video is removed and participants are explicitly asked to visualize the
movement observed in situation one. Again, they are instructed not to move
their hand. This is an explicit command that in convertion patients results in
inhibition of the motor cortex measured in the same way as above. (the cortex
is less active) This inhibition is expected to occur in CRPS patients.

TMS is a safe and pain-free study method. Only when TMS is used for a long
period of time or with a very high intensity , there is an increased risk of
seizures in people who are already familiar with epilepsy. This has never
happened with the duration and intensity used in this study. In addition,
people with a history of epilepsy are excluded.