Ataxia of parietal lobe origin.

Ataxia is the cardinal sign of cerebellar dysfunction and when it occurs, it indicates the possibility of cerebellar lesions. However, this may not always be the correct explanation. Appenzeller and Hanson1 reviewed studies, published between 1916 and 1953, of patients with cerebellar signs attributed to parietal lesions. Extensive lesions within the parietal lobes and sensory changes were common in these patients. They also reported on an adult who presented with pain and weakness of the left arm, lasting for 2 hours. When examined 2 weeks later, the limb was severely ataxic, but with no detectable weakness or sensory deficit. In addition, the patient had a dressing apraxia. At autopsy a small infarct in the arm area of the right postcentral gyrus was observed. The cerebellum and brainstem were normal. Ghika et al.2 reported on an adult patient who had a history of recurrent transient ischaemic attacks, with recent pronounced clumsiness of the right hand, accompanied for a few minutes by tingling of the lower-left half of the face and a left temporal headache. The right arm had decreased motility and hypotonia, but no weakness. The finger–nose test indicated hypermetria, asynergia, and dysdiadochokinesia; and rhythmic movements of the right hand were grossly abnormal. All these findings were no worse with the eyes closed. Slow distal mobility, with an equivocal plantar response without ataxia, was the only abnormality of the right leg. Repetitive testing revealed no evidence of any impairment of proprioceptive sensation. The CT scan revealed a cortico–subcortical parietal lesion in the left cerebral hemisphere, and a left posterior temporal arachnoid cyst. Abnormalities in the parietal and temporal regions were later confirmed by MRI scan. Angiography showed a 70% stenosis of the right internal carotid artery at the carotid syphon. No lesion or atrophy could be seen in the cerebellum or in its pathways in the brainstem, or in the thalamic nuclei or elsewhere in the white matter. These findings indicate that lesions in the posterior parietal area can mimic cerebellar ataxia, possibly by interrupting specific projections to the ventrolateral thalamic nuclei. Parietal ataxia is usually considered to result from a loss of proprioceptive feedback, interfering with the smooth execution of motor functions; and it is made worse by loss of vision. However, this was not the case in the patient Ghika et al.2 described. Therefore, it appears that parietal ataxia can occur with no sensory loss. Guard et al.3 described an adult with bilateral parietal lesions, a glioma on the left side and a haematoma on the right, who presented with Balint syndrome (loss of automatic eye movements) and who also had ataxia predominantly of the right hand. Steinlin et al.4 reported on two boys, aged 3 and 4 years, with congenital cerebellar ataxia; investigations suggested a parietal origin. At an early age both boys had evidence of overall delayed development. When examined at the age of 3 years, one boy had hypotonia with mild ataxia on reaching, and walked on a broad base with truncal ataxia. His features were mildly dysmorphic. The second boy presented at 6 months of age with infantile spasms which responded to treatment. However, he has since had occasional seizures. He had dysmetria at 1⁄2 years, and walked with a broad-based ataxic gait at 2⁄2 years. At age 4 years he had significant hypotonia and ataxia. The EEG of this patient was firstly hypsarrhythmic, and later indicated focal abnormalities in the parietal areas. The MRI in both boys revealed marked parieto–occipital pachygyria, while the cerebellum was normal. The family histories of both children were not significant. Congenital ataxia is usually due to infratentorial abnormalities, but in these two subjects the ataxia appeared to be related to the bilateral parietal lesions. A disruption of cerebello–thalamo–parietal connections could explain these findings. When reviewing non-progressive congenital ataxia, Steinlin et al.5 reported that some patients had no cerebellar hypoplasia and, although associated symptoms such as epilepsy and cognitive disabilities suggested supratentorial involvement, there was no definite evidence of parietal lesions. However, in the study of non-progressive ataxia by Esscher et al.6, a number of children had definite supratentorial abnormalities. Their motor disability was milder than those with infratentorial pathology. The lesions included cortical dysplasias and areas of abnormal migration, but localization to the parietal areas was not highlighted and some children had damage to various other areas of the brain. Other examples of non-progressive congenital ataxia have been recorded. For example, this diagnosis was given in two sisters who both had extensive neuronal migration abnormalities7. Their development was delayed. The eldest, at the age of 9 years, had nystagmus, intention tremor on finger–nose testing, and an unsteady broad-based gait. The white matter of the parietal lobes had low density areas with CT scanning, and the MRI revealed dilatation of the ventricles and basal cisterns, and thickening and abnormal smoothness of the cerebral cortex, especially in the frontal and parietal lobes. The white matter was generally thin, with multiple regions of abnormal signals supratentorially, and