[Mechanism of hypometria caused by pontocerebellar infarction]

By contrast to cerebellar hypermetria, the pathophysiology of cerebellar hypometria associated with a focal lesion is poorly understood. We describe a patient presenting an ischemic stroke involving the left lateral pons and middle cerebellar peduncle and exhibiting severely hypometric ballistic movements of the left wrist. Hypometria was associated with two distinct abnormalities of the triphasic electromyographic (EMG) pattern: a prolongation of the duration of the antagonist EMG activity and a reduced intensity of the agonist EMG activity. The first mechanism has been described previously in patients with a cerebellar disease and exhibiting hypometria, but not the second. The concomitant presence of these two elementary mechanisms contributed to the severity of hypometria in our patient. Moreover, this case illustrates that the integrity of the crossed pontocerebellar fibers passing through the middle cerebellar peduncle is necessary to generate an adequate agonist EMG activity.