Chapter 10 - Motor system examination

In this chapter we discuss the evaluation of the motor systems, that is the systems involved in generation and control of voluntary and reflex movements. The motor system can be divided into (1) the peripheral apparatus, which consists of the anterior horn cell and its peripheral axon, the neuromuscular junction, and muscle, and (2) the more complex central apparatus, which includes the descending tracts involved in control (i.e., the pyramidal system) and the systems involved in initiating and regulating movement (the basal ganglia and cerebellum).

Dysfunction in individual components of the motor system results in fairly specific abnormalities that can be evaluated at the bedside. Although multiple components may be involved (particularly with diseases of the central nervous system) isolated involvement of the various components commonly occurs. We will consider these components in order to help you establish an orderly approach to motor system evaluation (Table 10-1).

Examination for motor dysfunction includes assessment of strength, muscle tone, muscle bulk, coordination, abnormal movements and various reflexes. Many of these are best detected through simple (but careful) observation. However, a few maneuvers aid in the detection of abnormality. Table 10-2 lists the components of a comprehensive and efficient screening examination that will elicit and localize most motor system dysfunctions. If no abnormalities are found, this exam should only take two to three minutes in a cooperative patient. Table 10-3 lists the findings expected with diseases listed in Table 10-1, and Table 10-4 lists differentiating points between diseases affecting the nerves versus those primarily damaging muscle.

Elements of the examination

Examination of the motor system can be relatively objective and Tables 10-2 and 10-3 outline an approach using isolated segments of the motor system as models. Mixed-system involvements do occur with variable symptom and sign predominance, depending on such variables as the dominance of the various motor systems involved and the extent of the lesion(s) in each system. Lack of cooperation caused by patient fatigue, misunderstanding of the tasks demanded, or lack of physician-patient rapport must always be considered. Feigned or hysterical weakness, for example, usually can be distinguished by its bizarre localization, the absence of expected involvement of other systems (i.e., reflex, sensory, cranial), and the irregular ratchet-like giving way of muscles tested. It is always important to consider the implications of your findings and what additional or confirmatory test can be done to clarify and document your conclusions about the patient's motor system abnormality.

Strength

Strength is conveniently tested by having the patient resist your force as you attempt to move their body part against the direction of pull of the muscle that you are evaluating. This is graded on a scale of 0-5, with "0" representing absolutely no visible contraction and “5” being normal. A grade of "1" means that there is visible contraction but no movement;"2" is some movement but insufficient to counteract gravity;"3" is barely against gravity (with inability to resist any additional force); and "4" being less than normal (but more than enough to resist gravity). Obviously, there is ample range between 3 and 5, making the determination somewhat subjective. Some examiners expand the 5 point scale into a 9 point scale by the addition of “+” symbols when strength seems to be between numbers. Still others add “-“ symbols when a muscle seems to function just below a level. While there may be merit in having a scale beyond the original 5 points (particularly between 3 and 5) it must be remembered that the scale is quite arbitrary and lacks the precision suggested by the creation of many categories. Additionally, "normal" is a designation that takes into account the patient’s age and level of conditioning. This assessment can be made with greater precision when there is a normal side with which to compare it.

In order to test strength at various levels of the nervous system, several muscles must be tested. The more common of these muscles, along with their particular peripheral nerve and nerve root levels, are found in Table 10-5.

It is often very efficient to test patients using functional tasks rather than by manually testing each muscle. For example, the patient may be asked to hold the arms horizontally out in front with the palms up and eyes closed. Diffuse weakness of the upper limb often produces a “pronator drift”, i.e., downward drift of the weak limb with the hand pronating (turning in). If the limb drifts straight down, without pronation, this is not suggestive of physiologic weakness and the patient may have a conversion disorder or malingering. Erratic drift of the limb can be seen with proprioceptive sensory loss (confirmed by testing of proprioception). When testing strength in the legs it is helpful to have the patient attempt to walk on the toes and then heels. Other tests of the legs would include hopping on each foot, standing from a chair (without use of the hands) or climbing a stair. These latter tests examine more proximal muscles.

When confronting the patient with weakness, some assessment of effort should be made. Poor effort is usually reflected as good initial contraction, followed by a collapse (often termed "breakaway" or “collapsing” weakness). This is not a pattern seen in true neurologic injury where strength is typically inadequate but relatively constant. It is usually easy to detect the patient with "collapsing" weakness if you apply varying force during the muscle test. With true neurologic weakness, the maximum force that the patient applies does not vary appreciably. "Collapsing weakness" should not be graded. There are several potential causes of collapsing weakness, ranging from pain to the conscious embellishment of symptoms. When this pattern is seen, other more objective elements of the examination (such as reflex testing) become more important.

The ultimate goal of strength testing is to decide whether there is true "neurogenic" weakness and to determine which muscles/movements are affected. In correlation with the remainder of the motor exam, it should be possible to determine the particular part of the nervous system that is at fault to produce this weakness. Probably the most important decision is whether the weakness is due to damage to upper or lower motor neurons (UMN or LMN). As you may recall from Chapter 8, upper motor neuron weakness is due to damage to the descending motor tracts (especially corticospinal) anywhere in its course from the cerebral cortex through the brain stem and spinal cord. UMN weakness is typically associated with increased reflexes and a spastic type of increased tone. On the other hand, LMN weakness is due to damage of the anterior horn cells or their axons (found in the peripheral nerves and nerve roots). This results in decreased stretch reflexes in the affected muscles and decreased muscle tone. Additionally, atrophy usually becomes prominent after the first week or two, and this atrophy is out of proportion to the amount of disuse produced by the weakness.

"Deep tendon" (muscle stretch; myotatic) reflexes

The "deep tendon" (myotatic) reflexes are a critical part of the neurologic examination that is discussed in Chapter 8. Testing reflexes is the most important element of determining whether weakness is of an upper or lower motor neuron type (limited only by the fact that only certain muscles actually have reliably tested stretch reflexes). The commonly tested deep tendon reflexes include the biceps, triceps, brachioradialis (radial periosteal), quadriceps, hamstring and calf muscles (Achilles). Since the reflex arc includes stretch receptors and sensory fibers, it is not necessary to damage motor axons to abolish reflexes. However, in the setting of the patient with known weakness, reflex testing is a powerful tool to investigate the cause.

As you may recall from Chapter 8, symmetry of reflexes is the most important consideration in determining normality. Pathological "spread of reflexes" (i.e., contraction of muscles that produce motions other than the one associated with the test muscle) is another objective sign of hyperactivity. You may recall that sustained clonus (repeated muscle contraction when a muscle is passively stretched) is an indicator of hyperactive reflexes.

Conditions that damage lower motor neurons decrease muscle stretch reflexes by interrupting the reflex arc (Figure 8-1). Therefore, a diminished reflex in a weak muscle suggests damage to the lower motor neurons somewhere along the course to the muscle (i.e., anterior horn cells, motor nerve root, or peripheral nerve). Hyperactive reflexes are seen after damage to upper motor neurons (i.e., descending motor tracts). There are other confirmatory findings that may suggest upper or lower motor neuron disease. These signs include atrophy (LMN), fasciculations (LMN), spasticity (UMN), Babinski sign (UMN) or loss of superficial reflexes (UMN).

Superficial and "pathologic" reflexes

Superficial reflexes (abdominal, cremaster and plantar) are discussed in Chapter 8. These reflexes are mediated above the spinal cord. Therefore, disruption of the spinal cord or brain stem can abolish these reflexes. Of course, the superficial reflexes can also be abolished if there is extensive damage to sensory nerves or lower motor neurons in the region.

The "Babinski response" (up-going toe) is the classic pathological reflex seen with upper motor neuron damage. This reflex replaces the normal plantar response. The findings upon testing of superficial reflexes should be placed in the context of the remainder of the motor exam when evaluating upper and lower motor neurons.

Muscle Bulk

Muscle bulk is primarily assessed by inspection. Symmetry is important, with consideration given to handedness and overall body habitus. Generalized wasting or cachexia should be noted and may reflect systemic disease, including neoplasia. Some areas can be adequately evaluated by inspection alone, such as the thenar and hypothenar regions or the shoulder contour. Some areas, like the thigh, leg, arm and forearm, may be better evaluated by measurement. These measurements can also permit assessment over time.

Severe atrophy strongly suggests denervation of a muscle (such as with LMN lesions). This usually begins at least a week after acute injury and gets progressively worse with time (unless reinnervation takes place). Atrophy due to LMN damage must be distinguished from that which occurs secondary to disuse. However, there is usually a clear substrate for disuse (bed rest, cast, etc.) and there is little overall change in strength. Unfortunately, patients who have limited functional reserve (such a those with prior neural disease or the elderly) can be severely affected by disuse and deconditioning.

Coordination

Coordination is tested as a part of a sequence of movements. Typically the patient is asked to hold his/her hands in front with the palms up, first with the eyes open and then closed (as when examining pronator drift, above). It is usually good form to instruct the patient to prevent movement of his/her hands, and to exert some force either toward the floor or in attempting to push the hands apart. This force can be used to assess the strength of the patient and then should be released suddenly and without warning. After a short excursion, the patient should check this movement, and this checking should be symmetrical. The patient may then be asked to touch his/her nose, and subsequently the examiners finger. This can be repeated a few times to assess the smoothness and accuracy of the movement. Further assessment can be obtained by having the patient perform a rapidly repeated movement such as tapping the thumb and forefinger together, or by having the patient clap his hands. This test can be made somewhat more difficult by having the patient repeatedly strike first the palmar and then the dorsal aspect of one hand against the palm of the other. This, of course, must be done with each hand, and you are evaluating rhythmicity and speed in performance of the movement.

Lower extremity coordination can be tested in the supine position by having them attempt to place the heel of one foot on the opposite knee and subsequently tap or slide the heel down the shin to the ankle. This should be done with each leg. Other tests of lower limb coordination include tapping of the foot on the examiner’s hand, or attempting to draw a number in the air with his/her foot. If the patient can stand and walk, it is usually only necessary to evaluate gait in order to assess lower limb coordination. The patient who can stand on either foot for ten seconds without excessive sway does not need further testing of leg coordination.

These maneuvers test several neurologic systems. Strength is required for all of these tests. Excessive rebound (or loss of checking) is suggestive of cerebellar injury on the side of the abnormality. Similarly, difficulty with rapid alternating movements (dysdiadochokinesia) or marked overshoot or undershoot when attempting to hit a target (intention tremor) suggests cerebellar problems on that side. Repetitive over and undershoot during voluntary movement may reflect as "intention tremor". Extreme slowness of movement can be produced by extrapyramidal disease (such as Parkinson’s). Of course, problems with any part of the motor systems may affect coordination. For example, if there is a marked alteration in muscle strength, muscle tone, or if the patient is having abnormal movements this can influence your perception of coordination. Therefore, although tests of coordination are mainly directed toward assessing cerebellar function, you must decide whether other problems in the motor system are affecting these tests.

Muscle Tone

Muscle tone may be increased or decreased, with increased tone being much easier to detect. Tone can be assessed by one of two means. The most common method is for the examiner to passively move the patient’s limb (especially at the wrist). The second method involves evaluating arm swing (with the patient standing). Tone is often easily checked by having the patient stand with his/her arms hanging loosely at their side. When the patient’s shoulders are moved back and forth or rotated the arms should dangle freely. Increased tone is usually reflected as the arms being held stiffly both in the standing position and when walking. The lower limbs can be evaluated with the patient seated with the legs dangling. Movement of the feet should result in gentle swinging of the legs of a brief duration. Increased tone results in abrupt restriction on the excursion of the feet.

There are two common patterns of pathologically increased tone, spasticity and rigidity. Spasticity is found with upper motor neuron injuries and manifests as a marked resistance to the initiation of rapid passive movement. This initial resistance gives way and then there is less resistance over the remaining range of motion (clasp-knife phenomenon). Rigidity is an increase in tone that persists throughout the passive range of motion. This has been termed "lead pipe" rigidity and is common with extrapyramidal disease, especially Parkinson’s disease.

Many older individuals have another motor finding, called "paratonia." Paratonia is a phenomenon in which the patient is essentially unable to relax during passive movements. You will note that the resistance is irregular and generally greatest when you change the pattern of movement. Of note, most of these individuals have apparently normal tone when you test them in a standing position and move their shoulders about (as described above). Extreme paratonia is common in patients with dementia.

Some types of increased tone appear to be prolongations of voluntary muscle contraction. Myotonia is a slowness of relaxation of muscles after a voluntary contraction or a contraction provoked by muscle percussion. This is a disorder of striated muscle and not an abnormality of innervation and may be seen in conditions such as myotonic dystrophy or congenital myotonia (a disorder of ion channels). Occasionally, metabolic diseases of muscle (such as hypothyroidism) can result in myotonic discharges. Myotonia can be easily observed by asking the individual to reverse a muscle action quickly (i.e., trying to rapidly open a tightly clenched fist) or by tapping on a muscle belly (such as the thenar muscles). Neuromyotonia is a rare condition of irritability of the nerve (possibly autoimmune) where there is persistent contraction. Muscle contractions are not terminated and the patient becomes "stiff" with movement.

Abnormal movements

There are a number of types of abnormal movements including tremor, chorea, athetosis, dystonia, hemiballism and fasciculations. Each of these has clinical implications that require discussion.

Tremor is the most common abnormal movement seen in practice. Three characteristics are of particular importance. These include the symmetry (or asymmetry) of the tremor, the rate of the tremor (basically, whether it is fast or slow, i.e., greater or less than 7 cycles per second) and the circumstances under which the tremor is present (i.e., whether it is worst at rest, during sustained postures or when moving). Physiological tremor comes in two types. Rapid (>7cps) tremor is characteristic of states with increased sympathetic function (think of the last time you had too much coffee). This is most commonly secondary to anxiety, but may occur with increased adrenaline (such a pheochromocytoma) or thyrotoxicosis. A slower tremor must be classified with regard to the conditions in which it is most evident. If it is present predominantly at rest, and decreases with movement, this suggests extrapyramidal disease such as Parkinson’s disease (PD). In PD, the tremor is frequently asymmetrical and is usually associated with other signs (bradykinesia, rigidity or delayed postural corrections). Tremors which are severe on sustained postures (such as with the hands outstretched), but which may worsen slightly with action are characteristic of essential tremor (this is also seen in “senile” tremor or familial tremor). These tremors are absent at rest and are often worsened by anxiety. They are often asymmetrical and characteristically affect the use of writing and eating implements. Damage to cerebellar systems (particularly the hemispheres or dentate connections) often produces a tremor that is most pronounced during voluntary actions.

The second most common type of abnormal movement that is seen in practice is fasciculation. These are twitches in muscle (actually, contraction of a single motor unit, i.e., all of the muscle fibers attached to a single motor neuron). These can be felt and often seen. They are random and involuntary occurrences and do not result in movement of a joint. Fasciculations may reflect damage to lower motor neurons, either the cell body or the motor axon located in the nerve root or peripheral nerve. Of course, if the fasciculations were due to LMN lesions one would expect some weakness, decreased tone and (after a while) atrophy. Also, one would expect that the fasciculations would be persistent in a single group of muscles. Fasciculations may also be a temporary finding in overused muscles or as a sign of local muscle irritation. Also, there are some individuals who have “benign fasciculations,” particularly in the calf muscles. Of course, these are not associated with weakness or other motor system abnormalities.

There are several other, less common abnormal movements. Chorea is a rapid, fleeting, random and non-stereotyped movement which is worsened by anxiety and which can be suppressed for short periods by conscious effort. They differ from tics since tics are stereotyped and repeat within the same muscle groups. Tics may affect the voice, as well, and consist of repeated throat clearing, sniffing or coughing. Multiple vocal and motor tics are seen in Tourette syndrome. Athetosis is a slow, writhing, snakelike movement of a body part or parts. Dystonia is a sustained twisting of the body, usually the trunk or neck (where it is called torticollis). Hemiballism is a flinging motion of one side of the body, potentially resulting in falls.

Involuntary movements are seen in a number of clinical situations. Chorea, athetosis and hemiballism are reflections of basal ganglia disease. This may be congenital (a type of cerebral palsy), post infectious (Sydenham's chorea), hereditary (Huntington's chorea), metabolic (Wilson's disease) or cerebrovascular.

Station

This is the ability to maintain an erect posture. One should be able to stand both with the eyes open and closed with a relatively narrow base of support (the feet close together). You should record excessive sway, falling to one side, or marked worsening in the ability to stand when the eyes are closed.

Excessive sway with the eyes open is common with cerebellar or vestibular problems. This may be to one side (and commonly is with vestibular disorders) or may be to both sides (especially with conditions that affect the midline portion of the cerebellum, such as intoxication). You must consider the possibility of other explanations such as the patient not having enough strength to stay upright or severely delayed reactions to destabilization (such as with Parkinson’s disease). Some patients can stand well with the eyes open, but have marked increase in instability with the eyes closed. This is suggestive of a disorder of conscious proprioception (i.e., joint position sense, as may be seen with peripheral neuropathy or dorsal column/medial lemniscus dysfunction). This is termed a Romberg sign. Proprioceptive problems on one side can be brought out with standing on one foot. Of course, there are other tests of conscious proprioception, including evaluation of joint position and vibration sense in the feet. These data must be correlated with the findings on station.

Gait

This is an important part of any neurologic exam. It is particularly important to observe the symmetry of the gait, the ability to walk with a narrow base, the length of the stride when walking at a normal pace, and the ability to turn with a minimum of steps and without loss of equilibrium. When observing a normal person from behind, the medial parts of the feet strike a line and there is no space visible between the legs at the time of heel strike. This is a narrow-based gait and deviation from this can be measured in the amount of distance laterally each foot strikes from the line that their body is following. Tandem walking (the ability to walk on a line) may be used to evaluate for stability of gait, recognizing that many normal elderly patients have trouble with this.

Damage to virtually any part of the nervous system may be reflected in gait. An antalgic gait, or the limp caused by pain is familiar to any practitioner. Patients with unilateral weakness may favor one side, and if the weakness is spastic (i.e., from upper motor neuron damage) the patient may hold the lower limb stiffly. S/he will drag the weak limb around the body in a "circumducting" pattern. A staggering or reeling gait (like that of the drunk) is suggestive of cerebellar dysfunction. Generally, the patient with true vertigo will tend to fall to the one side repeatedly (especially with the eyes closed). A patient with foot drop will tend to lift the foot high (steppage gait). Hip girdle weakness often results in a "waddle," with the hips shifting toward the side of weakness when the opposite foot is lifted from the floor (of course, if both sides are weak the hips will shift back and forth as they take each step). Patients with Parkinson disease often have difficulty initiating gait; the steps are usually short, although the gait is narrow-based. If severe, the patient may be propulsive (they may even fall). Patients who are "glue footed" (sliding their feet along the ground rather than stepping normally) may be suffering from damage or degeneration of both frontal lobes or the midline portion of the cerebellum. When damage to these areas is severe the patient may be severely retropulsive (tending to fall over backwards repeatedly). Dorsal column injury may result in a gait in which the patient "stamps" his or her feet, and usually also needs to look at the feet in order walk. Patients with painful neuropathy of the feet may walk as if they are "walking on eggs" and patients with spinal stenosis may walk with a stooped posture (a "simian" posture).

Disorders of the Motor Systems

The reflection of motor system disease depends on the particular part of the motor system that is involved. Here we will discuss the characteristic deficits produced by lesions at each level of the motor system.

Muscle Disease (see Chapter 12)

Typically, muscle disease (myopathy) has its earliest and greatest effects on proximal musculature. There is little atrophy (until very late) and deep-tendon reflexes are decreased only in proportion to the weakness. Certain metabolic myopathies may result in cramping due to the fact that energy is required to relax muscles and myotonia may also produce difficulty in relaxation. There are no sensory changes in myopathy.

Neuromuscular Disease (see Chapter 12)

Myasthenia gravis is the prototypical neuromuscular disease. This condition results from autoimmune damage to acetylcholine receptors, which results in inefficient neuromuscular transmission. Initial contraction is strong but during sustained contraction, depletion of neurotransmitter results in progressive weakness. This can be seen during tonic actions (like simply holding up the eyelids or maintaining the arms out in front) or in actions that require sustained activity (like talking or swallowing a meal). For further information see Chapter 12.

Lower Motor Neuron (LMN) Damage (see Chapter 12)

These conditions occur due to damage to the anterior horn cells, the ventral roots or the peripheral nerves anywhere along their course to the muscles. In the majority of cases, the weakness is distal. The best explanation for the predominantly distal weakness in neuronal disease is that longer motor (also sensory) nerve fibers are more exposed and vulnerable to the many processes that damage nerves. An exception to this rule is the diffuse polyneuropathy of Guillain-Barre syndrome (presumed to be an autoimmune process). In this case weakness may begin in the proximal muscles and this is presumably because the primary damage to nerves is occurring quite proximally (near the nerve root level).

LMN disease results in weakness in the muscles connected with the affected nerve fibers. Understanding of the distribution of nerves and nerve roots to the individual muscles is essential to correct interpretation (Table 10-5). Additionally, there is atrophy (after the first week or two following an acute injury) that is out of proportion to simple disuse. Furthermore, reflexes are usually affected quite early and severely. This is because most conditions that damage LMNs also damage sensory nerve fibers that represent the afferent limb of the muscle stretch reflex. Finally, when there is damage to LMNs in peripheral nerves, there is often an accompanying sensory loss that can aid in diagnosis of the nerve that is involved.

Upper Motor Neuron Damage (UMN)

Historically, this has been associated with the corticospinal (pyramidal) tract. However, this is not quite accurate since voluntary motor pathways arising in the cerebral cortex can function by activating more primitive descending tracts from the brain stem. It is clear that the direct projections in the corticospinal tract are responsible for highly skilled movements, especially of the hands. In this section we will refer to direct and indirect corticospinal projections to distinguish the corticospinal tract itself from the indirect activation of other descending motor tracts by cerebral cortical input. Additionally, it must be understood that the motor cortex does not act independently, but rather under the influence of the premotor cortex (involved in planning and initiating movement) as well as "extrapyramidal" systems such as the basal ganglia and cerebellum (see below).

The classic picture of acute damage to UMNs includes contralateral paralysis of distal limb movements, while proximal limb movements are severely weakened and trunk movement minimally involved. Muscle tone (measured as passive resistance to manipulation) is depressed in this initial phase. The deep-tendon reflexes are also likely to be absent, recovering over time to normal or hyperactive levels. The superficial reflexes (abdominal and cremasteric) opposite the lesion are depressed or absent. A Babinski response is often present on the weak side.

Over weeks to months proximal strength improves to a significant degree, whereas distal movements make only a poor recovery. A rudimentary grasping capability is frequently all that remains in the hand. Extension, opposition, and individual finger movements remain severely affected or lost. Presumably, the recovery of proximal functions relates to some bilaterality of distribution of corticospinal fibers that innervate proximal muscles. The modest recovery of distal movements is suspected to relate to preserved motor pathways from the brain stem (presumably under extrapyramidal control).

Damage to the precentral gyrus (primary motor cortex) or isolated damage to the medullary pyramid produces a rather pure corticospinal tract lesion. In these cases, the weakness of distal muscles is severe but there is little appearance of other findings, such as spasticity and hyperreflexia that are hallmarks of most UMN lesions. Other UMN lesions also damage indirect descending connections between the cerebral cortex and spinal cord. This happens with lesions of the premotor cortex, corona radiata, internal capsule, cerebral peduncle, basal pons, and lateral columns of the spinal cord. Invariably, lesions in these areas also involve other pathways leaving the cerebral cortex that are intermixed with the direct corticospinal (pyramidal) projection. In addition to the weakness found in all of these patients, there is a decrease in tonic inhibition of reflexes and an increase in resting muscle tone. This is accompanied by hyperactivity of the deep-tendon reflexes and development of what is traditionally called spasticity.

Spasticity is an increased in muscle tone that is detected during passive movement of the limbs. The muscles at rest do not have excessive tone but any brisk stretch of a muscle group (particularly the flexors in the upper extremity and the extensors in the lower extremity) will result in a "catch" at about midlength of the muscle followed by a sudden release of the catch and relaxation of the muscle. The last two components, the catch and release, have been likened to a closing pen knife, which is the origin of the term "clasp-knife" spasticity. The overactive muscle stretch reflexes that are resonsible for spasticity are also the mechanism behind the hyperactive deep-tendon reflexes. The giving away or release portion of the clasp-knife phenomenon is presumed to be caused by increased firing of the inhibitory Golgi tendon organs, which produce an overactive reflex that inhibits the muscle.

If the lesion extends beyond the confines of the traditional corticospinal path, more descending pathways are involved and a greater degree of spasticity is noted; there also is a poorer recovery from weakness. This is presumably because of loss of more inhibitory influences on the segmental reflex arc and loss of more facilitatory influences on the motor neuron effector systems.

After very acute lesions of the descending motor systems there is often initial flaccid weakness that is sometimes followed by stereotyped movements and postures (decorticate posture, decerebrate posture or generalized withdrawal reactions)(Figure 10-1). Acute destructive lesions of the descending motor pathways cause a transient shock state of flaccid paralysis with loss of reflexes. When progressively greater amounts of the descending pathways are involved, a longer period of shock ensues. Acute cortical destruction may result in only hours to days of shock, whereas acute transection of the spinal cord can cause a shock state that persists for many weeks to months before spastic hyperreflexia and rudimentary spinal reflex behavior return. The precise pathophysiology of spinal shock is not clear, but it may complicate the evaluation of the patient following acute injury. It is always difficult to predict the final extent of the neurological injury in the setting of shock. Chronic or slowly progressive destruction of the descending motor pathways is not associated with a shock state. Presumably, this is because compensatory reorganization of the motor function occurs in equal pace with the losses.

Lesions that extensively destroy the cerebral cortex and basal ganglia, and preserve at least some of the diencephalon (like those caused by severe hypoxia) may result in stereotyped motor responses that involve flexion of the upper extremities and extension of the lower extremities. Noxious stimulation is usually necessary to elicit this reflex activity, which has been called decorticate posturing (Figure 10-1). It has been thought, on the basis of experimental data, that release of the rubrospinal motor system is, at least in part, responsible for decorticate posturing.

Transection of the brain stem, for example by stroke, at the level of the midbrain or pons is followed after a period of neuraxis shock by severe spasticity and reflex extension and pronation of the upper extremities with extension of the lower extremities and trunk on noxious stimulation (see Figure 10-1). This response is called decerebrate posturing and depends on preservation of the vestibular nuclei in the caudal brain stem, with the extension being produced by vestibulospinal pathways.

Lesions transecting the lowest portion of the brain stem or the upper spinal cord result in quadriplegia and severe spasticity after a period of shock. Later in the clinical course, reflex flexion movements of the limbs can be elicited by noxious stimulation (see Figure 10-1). These probably represent primitive spinal withdrawal responses.

As a rule, UMN lesions affect large areas of the body below the level of injury. It is often difficult to localize the specific level of damage by the pattern of weakness. Associated neurologic findings may clarify the level. For example, cranial nerve involvement or involvement of nerves or nerve roots may indicate a brain stem or spinal cord level of involvement, respectively, while cortical findings such as language difficulties, visual field abnormalities, dyspraxias, or other disorders of higher integrative function suggest cortical damage. In most UMN lesions, the whole side of the body below the lesion is affected (hemiparesis or hemiplegia). However, in the cerebral cortex the motor representation for the arm, face, and trunk lie within the supply of the middle cerebral artery, whereas the leg lies within the distribution of the anterior cerebral artery (Figure 10-2). Loss of middle cerebral cortical perfusion therefore causes a greater degree of weakness of the upper extremity than of the lower extremity. Occlusion of the anterior cerebral artery, an uncommon event, is associated with greater weakness in the leg than in the arm.

Because sensory and motor systems are near one another through the spinal cord, most of the brain stem and the cerebral hemispheres, it is common to have some sensory as well as motor symptoms. The sensory abnormality (see Chapter 9) may help localize the lesion. Pure involvement of UMNs without any sensory damage is most often seen with small lesions (usually vascular) in the posterior limb of the internal capsule or in the base of the pons.

Basal Ganglia Disease

The abnormalities associated with lesions and degenerative processes in the basal ganglia are discussed in some detail in Chapter 26. The findings are generally categorized into "hyperkinesias" and "hypokinesias." The classic picture of parkinsonism (the most common cause being Parkinson disease) includes bradykinesia (slow movements), rigidity, difficulty initiating movements and delayed postural corrections. These symptoms all fall into the category of "hypokinesia." There may also be a tremor at rest (suppressed by movement), which is a form of hyperkinesia. The rigidity of parkinsonism is present in all ranges of passive manipulation and cannot be abolished by sectioning the dorsal roots. Therefore, it is not due to reflex overactivity (deep tendon reflexes are normal in parkinsonism). It is probably due to tonic overactivity of the descending motor pathways and it can be abolished by cutting descending motor tracts (see Chapter 26 ). Other types of "hyperkinesia" include chorea, athetosis, hemiballism, tic and dystonia. These are indicative of dysfunction of the basal ganglia (extrapyramidal) system. However, they are not diagnostic of a particular cause (see Chapter 26 ).

Cerebellar Disease

Cerebellar disease produces predominantly motor symptoms. There are three main parts of the cerebellum, which have slightly different functions. The lateral cerebellar hemispheres (the neocerebellum) are involved in controlling distal limb movement of the ipsilateral limbs. The vermis of the cerebellum (midline) is involved in control of axial functions as well as the voice and eye movements. The posteroinferiorly-located vestibulocerebellum (floculonodular lobe; archicerebellum) is involved in vestibular functions and regulation of the vestibulo-ocular reflex (see Chapter 6).

Damage to the neocerebellum produces predominant symptoms of tremor, ataxia, and hypotonia. The tremor is of a particular type, consisting of rhythmic, variably 3-8 Hz oscillations that occur predominantly on voluntary activity and the tremor reaches its peak of oscillation toward the end of the movement. It disappears with posturing or at rest. It is noticed dramatically when reaching for objects (such as when performing finger-to-nose testing). The ataxia (incoordination) is manifest in several ways. There is dysmetria (past-pointing) with overshoot and/or undershoot of the target. Also, there may be a lack of checking (excessive rebound). For example, if the patient is asked to hold their hand extended out in front of them while pressure is applied and then suddenly released, there will be excessive movement before the patient "checks" the motion. Additionally, the patient will have difficulty performing rapidly repeated motions (tapping fingers, patting hands or tapping feet) and this may be even more obvious if there are rapid alternating movements involved in the motion (such as pronation and supination of the hands). Ataxia of the legs is manifest in difficulty in walking, often characterized by a broad-based and/or drunken gait.

Disorders affecting the midline cerebellum (vermis) affect axial motor activity. This is likely to be manifest as head and trunk instability as well as speech and eye movement problems. The problems with trunk stability are usually brought out during attempts to stand still or to walk. When there is both instability of the trunk and ataxia of the legs, patients will have severe ataxia. After vermal lesions, the speech may sound drunken or inappropriately staccato, and eye movements may be erratic and uncoordinated.

Because it is an important symptom of cerebellar disease, it would be appropriate to say a few more words here about ataxia. Cerebellar ataxia is fairly easy to observe in the office and it has at least two origins: (1) intention tremor of the legs, giving a dysmetric gait, and (2) truncal imbalance. If it is advanced, the patient has a wide-based compensatory gait, and if there is lateralized limb involvement, they tend to lean and fall toward the affected side. A sensitive test for ataxia is heel-to-toe tandem walking; this should be part of any neurologic screening examination in a patient with gait or balance complaints because it detects early cerebellar dysfunction. If the trunk alone is involved, as in early alcoholic degeneration or with a tumor of the vermis, there is a tendency to fall to either side, forward or backward. Some persons with midline cerebellar damage may have a stronger tendency to fall backward. This is called retropulsion and can also be seen in basal ganglia dysfunction (particularly parkinsonism) and in frontal lobe disorders. When retropulsion is due to cerebellar involvement, it frequently has an involuntary tonic character, i.e., the patients actually appear to be actively pushing themselves backward. Even at rest, sitting or standing, there is a tendency to lean or fall backward. With frontal lobe dysfunction and parkinsonism, the retropulsion is usually passive rather than active. This means that the patient has difficulty recovering from being pushed backward or from a backward-leaning position even though they may have no active or forced retropulsion at rest.

Damage to the vestibulocerebellum (flocculonodular lobe; archicerebellum) produces vestibular findings, including nystagmus that may be quite severe and in different directions depending on which way the patient is looking ("gaze-shifting nystagmus"). This is often more severe than symptoms due to vestibular damage since vestibulocerebellar damage is more difficult to compensate.

Finally, cerebellar damage can occasionally be reflected in hypotonia. The examiner should check for abnormalities of tone by asking the patient to relax and not resist. The limbs are then moved rapidly by the examiner in several ranges. A lack of resistance or a floppiness is noticed with hypotonia. Having the patient sit with his legs swinging free may test the legs. The leg is lifted by the examiner and released. Normally the leg swings back and forth several times and then stops, arrested by inertia and the normal resting muscle tone, which is a manifestation of the sensitivity of the normal muscle stretch reflex. With cerebellar hypotonia, the leg swings freely, unchecked, like a pendulum, arrested mainly by passive limb inertia.

References

Questions

Define the following terms:

spasticity, rigidity, hemiparesis/plegia, bradykinesia, paraparesis/plegia, upper motor neurons, lower motor neurons, internal capsule, chorea, athetosis, dystonia, hemiballism, tic, fasciculation.
Spasticity is a resistance to passive movements that is greatest at the initiation of motion (particularly of a rapid movement). It is often a sign of overactive muscle stretch reflexes.
Hemiparesis/plegia is paralysis or paresis (weakness) of one side of the body.
Rigidity is a smooth resistance to passive movement that occurs throughout the range of motion and usually results from extrapyramidal disorders such as Parkinson's disease.
Bradykinesia is a pathological slowing of motor performance often seen with Parkinson's disease and parkinsonism.
Paraparesis/plegia is paralysis or paresis of both lower extremities.
Upper motor neurons are the principal descending motor pathways for voluntary movement, including the corticospinal and corticobulbar tracts (and some other associated tracts).
Lower motor neurons are the anterior horn motor neurons and their axons that extend through the ventral nerve root and the peripheral nerves to reach the neuromuscular junction.
The internal capsule is the primary locus through which the upper motor neuron (corticospinal and corticobulbar) pathways descend.
Chorea is a purposeless, involuntary, random twitching movement.
Athetosis is a purposeless, involuntary writhing movement.
Dystonia is an involuntary, sustained twisting position of the body or a body part (torticollis, for example, when it involves the head).
Hemiballism a repeated, involuntary, flinging or flipping movement of a part of the body on one side, usually due to damage to the subthalamic nucleus.
Tic is a rapid movement, tending to be repeated in the same pattern over and over.
Fasciculation is an involuntary twitching of individual motor units, usually visible as a rippling of the skin but not resulting in any actual movement of the body part.

10-1. Describe the course of "upper motor neurons".

Answer 10-1. Upper motor neurons (corticospinal and corticobulbar tracts) arise in the motor cortex, traverse the internal capsule, cerebral peduncle and pyramids of the brain stem.

10-2. Over what functions do the upper motor neurons exert the greatest control (what movements are most affected by damage)?

Answer 10-2. They are mostly involved in control of distal movements (such as hand and fingers). Proximal functions (such as shoulder shrug) have bilateral control.

10-3. Where are sites of potential lesions producing lower motor neuron signs and symptoms?

Answer 10-3. Lower motor neuron damage can be anywhere along the pathway from the anterior horn motor neuron, ventral root, plexus or peripheral nerve.

10-4. What are the features of lower motor neuron damage?

Answer 10-4. Lower motor neuron damage results in decreased reflex and usually atrophy. It may also produce fasciculations.

10-5. What is the significance of fasciculations?

Answer 10-5. Diffuse, persistent and extensive fasciculations suggests motor neuron disease or damage (transient fasciculations are common and benign if unaccompanied by weakness or reflex change).

10-6. What are the characteristics of peripheral nerve damage?

Answer 10-6. Effects of nerve damage are most often seen distally, reflexes are affected early and atrophy is often present.

10-7. What are the characteristics of muscle disease?

Answer 10-7. Symptoms are usually most evident proximally, there is no sensory loss, reflexes only affected late and atrophy is not severe.

10-8. What are the characteristics of basal ganglia disease?

Answer 10-8. Muscle tone, postures, and patterned movements are most affected. Parkinsonism is common, with bradykinesia, difficulty initiating movements, delayed postural reflex responses and rigidity. Abnormal movements at rest are common: resting tremor, chorea, athetosis, dystonia and hemiballism.

10-9. What are the characteristics of cerebellar disease?

Answer 10-9. There are usually a variety of problems with coordination of voluntary actions, there may be trunkal ataxia (drunken gait) and muscle tone may be variably affected. Reflexes may be decreased or pendular.
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