Myoclonus and a number of other rapid involuntary movements have been difficult to classify clinically. Clinical and physiological analysis of a continuing series of patients has led to new classifications and pathophysiological insights. A series of patients with epilepsia partialis continue have been studied; the pathophysiology is heterogeneous, but in most electrophysiological techniques can identify an excitable region in cerebral cortex. A series of patients with adult onset tic have been analyzed and clinical rules have been formulated to make this diagnosis. Positron emission tomography (PET) studies of patients with palatal myoclonus have revealed that the inferior olives are hyperactive. PET studies of patients with hemiballimus have revealed that hypoactivity of the ipsilateral striatum occurs as a result of the lesion in the subthalamic nucleus. In studies of postural action tremors, we have been analyzing the amplitude of the tremor as a function of the precise posture of the limbs. For many tremors, such as cerebellar postural tremor, the tremor is worse when the arms are near the body and the hands are pointing towards each other. For other tremors this is not true, and the clinical and physiological significance of this is being explored. Task specific focal dystonias of the hands such as writer's cramp and pianist's cramp have been analyzed and a number of physiological characteristics have been defined. There appears to be diminished ability to control the fingers independently and gating of somatosensory evoked potentials with voluntary movement is abnormal. The spasms themselves have been characterized into different patterns. Abnormalities of the blink reflex have been identified in dystonic disorders. We have verified this in a number of our own patients and are now applying this test to the patients with focal hand cramps.
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