Complex regional pain syndrome (CRPS) is a condition of chronic pain and sensory changes that can occur after trauma to an arm or a leg. The initial injury may be minor or severe. Pain is the main feature of CRPS, but changes in blood flow to the skin, increased sweating, and swelling are common symptoms.
Movement disorders (MDs) such as tremor or dystonia develop in up to half the patients with CRPS. Dystonia is an abnormal twisting posture of the hand or foot. In this study from the Netherlands, patients with CRPS and dystonia are compared to patients with CRPS who do not have MDs.
The authors tried to find out what causes the MDs to develop. They looked at age, duration of symptoms, type of injury, and severity of symptoms as possible factors that cause MDs to develop. They were able to come to several conclusions after comparing the two groups.
First, the patients who developed dystonia were younger than patients in the group without dystonia. The length of time between the start of CRPS and the start of dystonia varies greatly. For some patients this interval of time was within one week. For others, the MD started up to five years later.
They found that once one extremity was affected, the chances of a second (or more) limb(s) developing dystonia increased greatly. It’s still not clear what causes dystonia to develop. It’s not linked to age, age, gender, or type of trauma. Disease duration or which limb is affected first doesn’t seem to make a difference either.
It looks like a central processing problem in the nervous system. There may be many neural circuits at multiple levels affected causing the problem. A change in function of nerve fibers capable of starting an inflammatory response may be the basis of the problem. The authors refer to this as a central circuit disorder.
There is a poor prognosis for CRPS patients who have dystonia. Finding out the underlying cause of the problem may help scientists find a way to prevent this from happening.