Coordination. Coordination of muscle movement requires that four areas of the nervous system function in an integrated way:
■ The motor system, for muscle strength
■ The cerebellar system (also part of the motor system), for rhythmic movement and steady posture
■ The vestibular system, for balance and for coordinating eye, head, and body movements
■ The sensory system, for position sense.
To assess coordination, observe the patient's performance in:
■ Rapid alternating movements
■ Point-to-point movements
■ Gait and other related body movements
■ Standing in specified ways.
ARMS. Show the patient how to strike one hand on the thigh, raise the hand, turn it over, and then strike the back of the hand down on the same place. Urge the patient to repeat these alternating movements as rapidly as possible.
Observe the speed, rhythm, and smoothness of the movements. Repeat with the other hand. The nondominant hand often performs somewhat less well.
In cerebellar disease, one movement cannot be followed quickly by its opposite and movements are slow, irregular, and clumsy. This abnormality is called dysdiadochokinesis. Upper motor neuron weakness and basal ganglia disease may also impair rapid alternating movements, but not in the same manner.
Show the patient how to tap the distal joint of the thumb with the tip of the index finger, again as rapidly as possible. Again, observe the speed, rhythm, and smoothness of the movements. The nondominant side often performs less well.
LEGS. Ask the patient to tap your hand as quickly as possible with the ball of each foot in turn. Note any slowness or awkwardness. The feet normally perform less well than the hands.
ARMS. Ask the patient to touch your index finger and then his or her nose alternately several times. Move your finger about so that the patient has to alter directions and extend the arm fully to reach it. Observe the accuracy and smoothness of movements and watch for any tremor. Normally the patient's movements are smooth and accurate.
Now hold your finger in one place so that the patient can touch it with one arm and finger outstretched. Ask the patient to raise the arm overhead and lower it again to touch your finger. After several repeats, ask the patient to close both eyes and try several more times. Repeat on the other side. Normally a person can touch the examiner's finger successfully with eyes open or closed. These maneuvers test position sense and the functions of both the labyrinth and the cerebellum.
LEGS. Ask the patient to place one heel on the opposite knee, and then run it down the shin to the big toe. Note the smoothness and accuracy of the movements. Repetition with the patient's eyes closed tests for position sense. Repeat on the other side.
Gait. Ask the patient to:
■ Walk across the room or down the hall, then turn, and come back. Observe posture, balance, swinging of the arms, and movements of the legs. Normally balance is easy, the arms swing at the sides, and turns are accomplished smoothly.
In cerebellar disease, movements are clumsy, unsteady, and inappropriately varying in their speed, force, and direction. The finger may initially overshoot its mark, but finally reaches it fairly well. Such movements are termed dysmetria. An intention tremor may appear toward the end of the movement (see p. 608).
Cerebellar disease causes incoordination that may get worse with eyes closed. Inaccuracy that appears with eyes closed suggests loss of position sense. Repetitive and consistent deviation to one side (referred to as past pointing), worse with the eyes closed, suggests cerebellar or vestibular disease.
In cerebellar disease, the heel may overshoot the knee and then oscillate from side to side down the shin. When position sense is lost, the heel is lifted too high and the patient tries to look. With eyes closed, performance is poor.
A gait that lacks coordination, with reeling and instability, is called ataxic. Ataxia may be due to cerebellar disease, loss of position sense, or intoxication. See Table 16-13, Abnormalities of Gait and Posture (pp. 618-619).
■ Walk heel-to-toe in a straight line— a pattern called tandem walking.
■ Walk on the toes, then on the heels— sensitive tests respectively for plantar flexion and dorsiflexion of the ankles, as well as for balance.
Tandem walking may reveal an ataxia not previously obvious.
Walking on toes and heels may reveal distal muscular weakness in the legs. Inability to heel-walk is a sensitive test for corticospinal tract weakness.
■ Hop in place on each foot in turn (if the patient is not too ill). Hopping involves the proximal muscles of the legs as well as the distal ones and requires both good position sense and normal cerebellar function.
■ Do a shallow knee bend, first on one leg, then on the other. Support the patient's elbow if you think the patient is in danger of falling.
Difficulty with hopping may be due to weakness, lack of position sense, or cerebellar dysfunction.
Difficulty here suggests proximal weakness (extensors of the hip), weakness of the quadriceps (the extensor of the knee), or both.
■ Rising from a sitting position without arm support and stepping up on a sturdy stool are more suitable tests than hopping or knee bends when patients are old or less robust.
People with proximal muscle weakness involving the pelvic girdle and legs have difficulty with both of these activities.
Stance. The following two tests can often be performed concurrently. They differ only in the patient's arm position and in what you are looking for. In each case, stand close enough to the patient to prevent a fall.
THE ROMBERG TEST. This is mainly a test of position sense. The patient should first stand with feet together and eyes open and then close both eyes for 20 to 30 seconds without support. Note the patient's ability to maintain an upright posture. Normally only minimal swaying occurs.
In ataxia due to loss of position sense, vision compensates for the sensory loss. The patient stands fairly well with eyes open but loses balance when they are closed, a positive Romberg sign. In cerebellar ataxia, the patient has difficulty standing with feet together whether the eyes are open or closed.
TEST FOR PRONATOR DRIFT. The patient should stand for 20 to 30 seconds with both arms straight forward, palms up, and with eyes closed. A person who cannot stand may be tested for a pronator drift in the sitting position. In either case, a normal person can hold this arm position well.
The pronation of one forearm suggests a contralateral lesion in the corticospinal tract; downward drift of the arm with flexion of fingers and elbow may also occur. These movements are called a pronator drift, shown below.
Now, instructing the patient to keep the arms up and eyes shut, as shown above, tap the arms briskly downward. The arms normally return smoothly to the horizontal position. This response requires muscular strength, coordination, and a good sense of position.
A weak arm is easily displaced and often remains so. A patient lacking position sense may not recognize the displacement and, if told to correct it, does so poorly. In cerebellar incoordination, the arm returns to its original position but overshoots and bounces.
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