[Frontal pseudoataxia, discussion on its mechanism (author's transl)].

We presented a rare care who had right frontal lobe infarction, with left side pseudoataxia, and the mechanism, causing pseudoataxia, was considered. The patient, a 51 year-old, righ-handed male, was admitted on August 9, 1980, complaining of left-side pseudoataxia. About p.m. 7:00, July 29, 1980, he suddenly noticed numbness of the left foot, and he found himself difficulty in standing in the next morning. He had a mild paresis and tactile-tactile of the left side including the face, which was rapidly improved. However, there was pseudoataxia of the left extremities, which had not been improved. On physical examination, dysarthria, aphasia, finger agnosia, difficulty in right left orientation or muscle weakness was not recognized, and there was no sensory disturbance except for slight impairment of stereognosis, two point discrimination and vibratory sense. Demonstrable impairment of tactiletactile from was observed in the left hand. Notable dysmetria, terminal tremor and dysdiadochokinesia were seen in the left limbs, which were remarkably worsened with eyes closed. However, tapping and line-drawing tests were normal. Babinski-Weil's test disclosed typical compass gait. There was marked swaying in Romberg position. Tandem gait was impossible with a tendency to decline the left. Deep reflexies were normal except for mildly hyperactive radial reflex in the left. Carotid and vertebral angiographies revealed neither evidence of vascular occlusion nor displacement of vessels CT scan demonstrated a low density area, which included the right inferior and middle frontal gyri, the head of the right caudate nucleus and a part of anterior crus of right internal capsule. There was enlargement of anterior horn of the right lateral ventricle. Caloric test, electronystagmography, eye tracking test or optokinetic nystagmus test disclosed no abnormalities. Vibration induced falling, which is the postural reaction to muscle vibration during standing (Ekuland, G., 1972), was not recognized when the left Achiles' tendon was stimulated. Pseudoataxia of this patient differed from the typical cerebellar or vestibular ataxia. From a review of the literatures concerning frontal pseudoataxia, almost all cases had no distinct cerebellar signs, and showed positive Romberg's sign. The impairment of tactile-tactile form and postural reaction to vibratory stimulation to the left leg, appeared in this case, could be hardly explained by the lesion of parietal lobe or deconnection syndrome. Sensory perception of parietal lobe and pyramidal motor system were thought to be almost normal in this case. Therefore, these findings should be due to impairment of integration center between sensory and motor systems. The pseudoataxia in frontal lesion seems to occur as the results of involvement of this center, in which caudate nucleus maybe has important role, but not as the results of disturbances in the front-ponto-cerebellar or front vestibular pathway.