PET and SPECT Imaging in Dystonia

Dystonia is a syndrome characterized by involuntary, sustained muscle contrac- tions causing twisting movements and abnormal postures. It is a common move- ment disorder with different forms that can be classified based on different clinical characteristics. Sporadic 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 underly- ing genetic defect. The mode of inheritance is usually autosomal dominant. Of these, the most common are DYT1 and DYT6 dystonia. In dystonia-plus syn- dromes, also autosomal dominantly inherited disorders, dystonia patients have additional neurological symptoms (e.g., parkinsonism or myoclonus). This group includes dopa-responsive dystonia, myoclonus-dystonia, rapid-onset dystonia- parkinsonism, and paroxysmal dystonia. In this chapter, we describe results from PET and 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 rCBF activation studies dif- fered 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 dopa- mine D2/3 receptor binding in the striatum of patients with almost all forms of dystonia. In conclusion, dystonia is likely to be a network disorder with abnor- malities 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.