Lesions in the cerebellum cause either truncal dysfunction in midline lesions of the vermis or ipsilateral dysfunction for hemispheric lesions. The signs consist of ataxia, past pointing and hyporeflexia. The diagnosis of a cerebellar lesion has to be by exclusion. An ipsilateral hemispheric cerebellar localization can only be made in the context that the lower motor unit, upper motor unit, sensory system (spinocerebellar tract and posterior columns) are intact.

A common mistake made by students is for example in a patient with a lesion of the right internal capsule to localize it as a left cerebellar lesion due to ataxia of the left arm. In this case the ataxia of the left arm is due to the dysfunction of the upper motor neuron unit damaged by the right hemisphere lesion. The clinical picture clarifies the situation in that the right hemisphere lesion will often be associated with upper motor neuron pattern of weakness and hyperreflexia of the left upper limb.

Symptoms and Signs

• Unilateral symptoms of dysarthria, dysmetrias and dysdiadokinesia with lack of sensory, lower motor, and upper motor findings

• Lesions are ipsilateral to side of signs

• Midline lesions affect posture and gait more than hemispheric lesions which affect upper and lower limb movements

• Pendular reflexes