Transcranial sonography in dystonia

Objectives: In idiopathic dystonia (ID) electrophysiological and functional neuroimaging studies demonstrate a disinhibition of thalamic and motor cortex neurons, pointing towards a key role of basal ganglia in the pathogenesis of ID. Transcranial ultrasound (TCS) studies were able to display changes in echogenicity in various regions of the brain in patients with Parkinson's disease and affective disorders although conventional MRI and CT usually remain normal as they do in ID. Therefore, patients with different manifestations of ID or tardive dystonia underwent TCS examinations in order to describe basal ganglia echomorphology in these disease entities.

Methods: TCS examination was done as described earlier. Through the preauricular bone window the hypoechogenic brainstem can be shown. By tilting the probe upwards the ventricular plane is displayed. The ventricles surround the basal ganglia which are normally homogenously hypoechogenic and cannot be distinguished from each other. Special attention was paid on localized or diffuse shifts of echogenicity in this area.

Results: In several studies a total of 114 patients were examined. Patients with cervical, upper limb, facial, segmental and generalized manifestation forms, tardive dystonia and dopa-responsive dystonia were included. 69 patients showed a hyperechogenicity of the medial part of the lentiform nucleus corresponding to the globus pallidus internus (GPI) (61%). In a separate analysis facial dystonias turned out to be mostly normal (31% hyperechogenic GPI uni- or bilaterally), no hyperechogenicity was found in tardive and dopa-responsive dystonia. Excluding these patients, 85% with focal, segmental and generalized manifestations of ID showed the TCS abnormality. Out of 70 control subjects 63 were normal (90%). Intergroup difference was statistically significant.

Discussion: TCS supports the hypothesis of basal ganglia alteration in the pathogenesis of ID as it shows a characteristic GPI hyperechogenicity in a majority of patients. Differences in the echopattern between the subgroups of manifestation of ID raise the question of different pathogenetic pathways leading to different dystonic symptoms. In clinical practice, this leads to the possibility that TCS could contribute to the diagnosis of ID in differentiation from tardive and psychogenic forms of dystonia. Driven by the TCS findings, possible reasons underlying the echoshift in dystonia patients are discussed.