Motor dysfunction in CRPS and its treatment.

Complex Regional Pain Syndrome (CRPS) is a relatively new term for a clinical entity first described during the American Civil War almost a century and a half ago. Historically, the diagnostic criteria have focused on the sensory (pain, allodynia, hyperalgesia) and autonomic (sudomotor and vasomotor disturbances) features associated with this syndrome (IASP terminology Refs. [10,14]. However, recent epidemiological reports and studies attempting to validate the International Association for the Study of Pain (IASP) diagnostic criteria have documented that motor dysfunction is common in CRPS [1,4,13,19]. An expert consensus panel has proposed revised diagnostic criteria for CRPS which include the presence of motor signs and symptoms [7]. The majority of patients with CRPS exhibit a variety of motor symptoms and signs including weakness, tremor, decreased range of movement, difficulty in performing complex movement patterns, dystonia, and myoclonus [1,8,11,19]. Focal distal limb dystonia and myoclonic jerks have been reported in 30% of patients [1]. The prevalence of motor disorders may increase with prolonged duration of the disease and may reach as high as nearly 50% of patients [11,19]. In late stages, contractures from guarding of the affected limb and fibrosis of palmar and plantar fascia may also be observed. Although these motor symptoms are restricted to the affected limb in most patients, in a subset of patients these symptoms spread to other extremities [11]. Among the motor dysfunctions seen in patients with CRPS, dystonia is often disabling and presents a therapeutic challenge [18]. Dystonia, a neurological movement disorder, is characterized by sustained muscle contractions that result in twisting and repetitive movements or abnormal postures [2]. Although many dystonias have no known cause and are termed primary dystonias, numerous hereditary neurodegenerative disorders, such as Parkinson’s disease, Huntington’s disease, Wilson’s disease, and Rett syndrome, are associated with secondary dystonias. Many drugs, including levodopa, dopamine agonists, antipsychotic drugs, anticonvulsant agents, and serotonin-reuptake inhibitors, also can cause dystonias [15]. Studies in patients with dystonia have indicated that the disorder might result from alterations in the sensorimotor circuitry that integrates sensory input and motor output [2]. Imaging studies in patients with secondary dystonias have commonly revealed damage to the basal ganglia, but multiple other regions including the thalamus, brainstem, parietal lobe, and cerebellum may also be involved [6,9]. Impaired inhibition at multiple levels of the central nervous system has been suggested as potential pathophysiological mechanisms for dystonia [2]. Possible examples include disruption of the striatal dopaminergic and cholinergic neurotransmitter systems and a loss of GABA-mediated inhibition. Plastic changes in central sensory and motor nervous systems have similarly been reported in CRPS patients [3]. Functional imaging studies have shown shrinkage of cortical hand representation