| Dystonia is the term for a set of disorders characterized by abnormal postures and unwanted muscle spasms that interfere with motor performance. Adult onset idiopathic focal dystonias are the most common and refer to dystonia of one body region. These disorders are characterized by abnormal co-contraction of antagonist muscles and include benign essential blepharospasm (BEB), which refers to dystonia of the eyelid and surrounding eye and facial musculature; and focal hand dystonia (FHD), the most common form is writer's cramp (WC). While these disorders are not life threatening, severe symptoms can result in permanent physical disability, mental anguish and an overall decrease in the quality of life. Currently, results from neuroimaging studies to determine the pathogenesis of focal dystonias implicate an environmental component and a dysfunction in structure and function of the brain; however, pathological and neuroradiological data are sparse and controversial, leaving the underlying cause of focal dystonias not well understood. The goal of these studies was to understand the pathophysiology of focal dystonias, specifically Writer's Cramp and Blepharospasm, looking at brain structures as a whole with close attention to the cortical and subcortical regions responsible for motor control using highly refined magnetic resonance imaging (MRI) techniques. Results from this study may suggest new leads for treatment and therapy of focal dystonias. First, I studied gray matter volume changes in patients with Blepharospasm compared to age-and gender-matched healthy volunteers to determine if there is a structural abnormality in this patient population. Second, I identified the handwriting motor program in a population of healthy volunteers, to determine functional brain activations of writing compared to tasks similar to and unlike handwriting. Third, I studied the function of the handwriting motor program in Writer's Cramp patients compared to age- and gender- matched healthy volunteers to evaluate the phenomena of task specificity and determine its potential role in the pathophysiology of this disorder. We observed a gray matter volume increase in the putamen in BEB patients. This putaminal change may lead to a disturbance in the normal function of the blink system. In WC patients we observed a trend for hyperactivation of the primary sensory and motor cortices and hypoactivation of the premotor areas involved in the handwriting motor network. These results suggest a dysfunctional basal ganglia---cortical network, which is compatible with a loss of inhibition during the generation of motor commands and may be responsible for dystonic movements. Information from these studies could be used to provide new ideas for therapies of focal dystonias. |
