PET and SPECT Imaging in Dystonia

Dystonia is a syndrome characterized by involuntary, sustained muscle contractions causing twisting movements and abnormal postures. It is a common movement disorder with different forms that can be classified based on different clinical characteristics. Idiopathic focal dystonia (dystonia in one body part with no known cause) is the most common form. The more generalized (throughout the body) forms of dystonia have a younger age of onset and usually an underlying genetic defect. The mode of inheritance is usually autosomal dominant. Of these, the most common are DYT-TOR1A and DYT-THAP1 dystonia. In combined dystonia syndromes, also autosomal dominantly inherited disorders, dystonia patients have additional neurological symptoms (e.g., parkinsonism or myoclonus). This group includes dopamine-responsive dystonia, myoclonus-dystonia, rapid-onset dystonia-parkinsonism, and paroxysmal dystonia. In this chapter, we describe results from positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies in the different forms of dystonia. Three different kinds of PET and SPECT techniques have been used in patients with dystonia: glucose metabolism scans, regional cerebral blood flow studies, and receptor imaging. Increased glucose metabolism was found in the basal ganglia, thalamus, and cerebellum of patients with different forms of focal dystonia and in DYT1 dystonia. Patients with DYT6 dystonia showed decreased glucose metabolism in the putamen. Results from regional cerebral blood flow (rCBF)-activation studies differed extensively among different studies and different patient groups, mainly because of study design. Overall, the primary and secondary motor and sensory cortices were found to be abnormal in almost all forms of dystonia, although the direction of the abnormalities differed. Dopamine was found to play a role in dystonia reflected by decreased dopamine D2/3 receptor binding in the striatum of patients with almost all forms of dystonia. In recent years, it has been established that other neurotransmitter systems, such as serotonin and gamma aminobutyric acid (GABA) also play a role in dystonia. In conclusion, dystonia is likely to be a network disorder with abnormalities in a large number of cortical and subcortical areas. There might be a central role for the basal ganglia with abnormalities in dopamine receptor binding, as well as other neurotransmitter systems.