Fine movements of the hands and feet, as discussed earlier under the general motor exam, should be tested. Rapid alternating movements, such as wiping one palm alternately with the palm and dorsum of the other hand, should be tested as well. Perhaps the most popular test of coordination, however, is the finger—nose—finger test, in which the patient is asked to alternately touch their nose and the examiner's finger as quickly as possible. Ataxia is best revealed if the examiner's finger is held at the extreme of the patient's reach, and if the examiner's finger is occasionally moved suddenly to a different location. Test for overshoot by having the patient raise both arms suddenly from their lap to the level of your hand. In addition, you can apply pressure to the patient's outstretched arms and then suddenly release it. To test the accuracy of movements in a way that requires very little strength, you can draw a line on the crease of the patient's thumb and then ask the patient to touch the line repeatedly with the tip of their forefinger.
Similar tests can be done with the legs. In the heel—shin test the patient is asked to touch the heel of one foot to the opposite knee and then to drag their heel in a straight line all the way down the front of their shin and back up again. In order to eliminate the effect of gravity in moving the heel down the shin, this test should always be done in the supine position. Testing for ataxia is discussed further in Neuroanatomy through Clinical Cases, Key Clinical Concepts 15.2.
Normal performance of these motor tasks depends on the integrated functioning of multiple sensory and motor subsystems. These include position sense pathways, lower motor neurons, upper motor neurons, the basal ganglia, and the cerebellum. Thus, in order to convincingly demonstrate that abnormalities are due to a cerebellar lesion, one must first test for normal joint position sense, strength, and reflexes and confirm the absence of involuntary movements caused by basal ganglia lesions. As already mentioned, appendicular ataxia is usually caused by lesions of the cerebellar hemispheres and associated pathways, while truncal ataxia (see Romberg Test and Gait ) is often caused by damage to the midline cerebellar vermis and associated pathways (see Neuroanatomy Through Clinical Cases, Figures 15.3, and 15.9).