[A patient with focal dystonia induced by golf and presenting a decrease in activity of cerebral motor cortex on task].

We here report a 45-year-old man with left arm focal dystonia induced by golf. He was a swimming instructor. From 35 years of age, he swung a golf club for 4 hours everyday. At 37 years of age, he noted difficulties in moving left arm when swinging, and developed involuntary movement of left arm toward his back thereafter. His involuntary movement was exacerbated even in several years after stopping both golf and swimming. Neurologically, simultaneous contraction was observed in left triceps and biceps muscles and his left arm dropped when raising arm to front. A 'sensory trick' was also observed. Thus, he was diagnosed as having a rare focal dystonia, and its clinical characteristics and course were basically different from those of 'yips', a focal dystonia that is characterized by anxiety and distal dominant dystonia presenting only on golf. Magnetic resonance imaging (MRI), FDG-positron emission CT (FDG-PET), C11-Raclopride PET and 99mTc-single photon emission CT (SPECT) revealed no abnormality in cerebral cortex and basal ganglias. However, motor evoked potentials (MEPs) were not evoked bilaterally when magnetic stimulation was applied on primary motor cortex. On functional MRI (fMRI), 40 seconds raising left arm task-induced activation in the right primary motor, supplementary motor, and premotor areas was apparently decreased, while left motor areas, the normal side, were reasonably activated. Motor-associated areas are generally overactivated by task in focal dystonia patients whereas excitability in primary motor area is decreased in idiopathic generalized dystonia. Therefore, dystonia of the present case appears to be similar to focal dystonia clinically but may partly have a mechanism similar to idiopathic generalized dystonia as shown in the fMRI studies.