Chapter 15 - Evaluation of the Ataxic Patient
Ataxia is defined as a difficulty of gait. It is a very common neurologic complaint, particularly in an elderly population and is often multifactorial. In general terms, ataxia can result from damage to the sensory systems that provide feedback for normal balance, or problems with the several motor systems that are needed to respond to the constantly changing environment while walking.
The sensory systems that are important to gait include the visual system, the vestibular system and the conscious proprioceptive system from the lower limbs (especially the feet). When one of these systems is not functioning (such as when the eyes are closed) one becomes more dependent on the others. There are also certain times when one becomes more dependent on the sensory systems (such as the dependency on sensations from the feet when the ground is rough or irregular). Also, when a sensory system is functioning abnormally (such as when the patient has vertigo from abnormal vestibular function) it becomes difficult to maintain normal balance.
The motor systems that are necessary for normal gait include those responsible for strength (upper and lower motor neurons), coordination (the cerebellum) and muscle tone and postures (the extrapyramidal system). Also, there are cortical elements necessary for gait that will be discussed below.
Finally, there are patients who cannot stand due to other factors, such as orthostatic hypotension, that occur when upright.
There are several questions that can aid in focusing the evaluation.
How long has it been present and did it begin all of sudden? These are common questions in neurology and help distinguish chronic and slowly progressive problems (such as degenerative diseases like Parkinson disease) from acute problems (like stroke).
When does it occur? It is important to note the circumstances under which the patient's gait is notably abnormal. For example, if walking on irregular surfaces or in the dark markedly worsens the patient’s gait, sensory ataxia should be a major consideration.
Are there any coexisting symptoms? These may include vertigo, weakness, stiffness or slowness of movement, abnormal movements, cognitive difficulties or significant changes in behavior. These can be clues to vestibular, cerebellar, pyramidal, extrapyramidal or frontal lobe disorders. Feelings of presyncope may require evaluation of factors potentially affecting blood flow to the brain (Chapter 27).
What have been the functional ramifications of the gait disturbance? For example, has the patient fallen and, if so, in what situations? What has the patient or family done to prevent falls (i.e., restrict movements, etc).
Is the gait disturbance completely explainable by pain (such as a limp), or by compensation for weakness of a single muscle group? If it is due to weakness, evaluation of this symptom (Chapter 12) will be the most important factor.
Is the gait disturbance real and have others noticed it? This is important because ataxia can be hysterical in nature. At times this can be recognized by the severity of the gait disturbance (which is often exaggerated and bizarre) and the relative paucity of injuries due to falls, etc. These patients often “catch themselves” in ways that would suggest higher levels of motor performance than their poor gait would indicate. Astasia-abasia is a term that has been applied to the condition in which the patient lurches wildly and only falls when there is someone or something to break the fall. The key to recognizing this is to realize that the ability to catch themselves exceeds that which would be expected of a patient with such severe gait disturbance.
The examination of the patient with ataxia is focused on evaluating those systems necessary to maintain the upright posture. During portions of the neurologic examination, screening tests of strength, muscle tone, coordination, the vestibular system, the conscious proprioceptive system, and cortical function (especially the frontal lobes) must be included. Of course, it is most critical to watch the patient walk. Patients with ataxia tend to compensate by broadening their base of support (normally, the medial side of each foot strikes along a straight line when walking). Examining the patient's posture when standing with the feet together is important. If they are steady with the eyes open but not with the eyes closed (Romberg sign), loss of proprioception in the feet should be suspected.
Conscious proprioceptive sensory system. One of the most common causes of ataxia is loss of proprioception in the feet. This can be tested by examining vibratory and joint position sense at the great toe. These patients have worsened symptoms when walking on irregular surfaces or when their vision is obscured and they usually broaden their base of support. They also have trouble standing with their eyes closed (Romberg sign) and the ataxia markedly improves simply by touching a stationary object or running the hand along the wall (in a sense, replacing the lost sensitivity of the feet). Although elderly patients often lose some sensitivity at the toes, the various causes of polyneuropathy or dorsal column damage should be considered if the sensory loss is out of proportion for age. It is noteworthy that these patients improve dramatically when walking with a cane.
Vestibular system. Vestibular problems are usually easy to recognize by history and exam. The patient is likely to be vertiginous and will usually show nystagmus that is at least in proportion to their vertigo. They will tend to veer to one side when they try to walk a straight line. The evaluation of such patients is conducted according to the protocol for evaluating the dizzy patient found in Chapter 14.
Cerebellar system. The ataxia of cerebellar disease tends to produce a broad-based, lurching, reeling or drunken kind of gait. The ataxia often involves the trunk with titubation. The symptoms of imbalance are usually manifest while trying to stand with the feet together even with the eyes open. Eye closure usually only slightly worsens the imbalance. Most often, patients have other signs of cerebellar disease, such as speech disturbance or incoordination of the limbs. The broad differential diagnosis of cerebellar disease can be found in this table.
Strength. It is important to consider whether the patient has adequate strength to stay upright. If weakness is an issue, do they have signs of upper motor neuron damage (hyperactive reflexes, spasticity or Babinski sign) or lower motor neuron damage (diminished reflexes, atrophy or, possibly, fasciculations). Do they have a weakness that suggests myopathy (proximal – hip and shoulder girdle) or generalized neuropathy (distal). If the patient is weak, it is essential to assess whether their degree of gait difficulty is fully explained by the weakness.
There are several very specific gait disturbances associated with weakness. For example, weakness of the hip girdle muscles causes the pelvis to shift toward the side of weakness when walking. When the hip girdle weakness is bilateral the gait is described as "waddling." A foot-drop will cause the patient lift that leg higher, and the gait disturbance is called a “steppage” gait. Weakness of the quadriceps muscles will cause the patient to swing the affected leg forward and lock the knee at the time of heel-strike in order to prevent the leg from collapsing.
Extrapyramidal system. Extrapyramidal disorders, such as Parkinson disease, commonly affect gait. In the case of Parkinson disease, patients tend to have rigidity with slowed movements. They have slowed or delayed postural corrections when they are bumped off balance. Curiously, they tend to walk with a narrow base of support, which is counterintuitive. Most of the other causes of extrapyramidal gait disturbance result in some broadening of the base of support. Some of these other conditions also produce dystonia or limitations of vertical gaze. Additionally, there may be other abnormal movements at rest. These signs and symptoms are usually detected by carful observation during the exam.
Frontal lobes. Damage to the frontal lobes, often produces a curious kind of gait disturbance called “apraxia” of gait. The patient tends to slide their foot along the floor instead of lifting and placing normally. This has been called a “glue-footed" or "magnetic" gait, and the patient may be retropulsive if this is severe. Primitive reflexes such as grasp, snout, palmomental and glabellar responses are likely to be disinhibited, and the patient's personality or cognitive function are often impaired. When severe, these kinds of frontal lobe conditions may result in incontinence, which typically occurs without warning. Conditions such as frontal lobe strokes, tumors or normal pressure hydrocephalus should be considered as possible causes, although generalized dementing illnesses can also involve frontal lobes. In patients with generalized dementia, such as Alzheimer disease, gait disturbance is usually found in the latter stages.
In summary, the evaluation of any ataxia requires assessment of those systems that are necessary to maintain the upright posture. In the elderly, the problem may well be multifactorial. Nonetheless, each of the problems that may be contributing to the gait disturbance requires investigation in order to determine whether further deterioration can be prevented. Remediation of the gait disturbance may be relatively simple (such as the use of a cane in patients with sensory ataxia or braces in patients with focal weakness). Additionally, specific treatment of disorders such as Parkinson disease may result in dramatic improvement in gait. It is important to be systematic and aggressive in the evaluation and management of gait disturbance since this symptom is not only terribly limiting for patients, but also because falls represent a major health risk, especially in the elderly.
Define the following terms:Ataxia, dysequilibrium, sensory ataxia, astasia-abasia, gait apraxia.
15-1. What systems are important to normal, safe ambulation?
15-2. What gait disturbance is seen with pain?
15-3. What kind of gait disturbance would you expect to see in the patient with dysfunction of conscious proprioception (either a large fiber polyneuropathy or dorsal column damage)?
15-4. What symptoms would suggest vestibular abnormality as the cause of ataxia?
15-5. What symptoms would suggest cerebellar abnormality as the cause of ataxia?
15-6. What role does strength play in gait?
15-7. What symptoms would suggest extrapyramidal abnormality as the cause of ataxia?
15-8. What symptoms would suggest frontal lobe disease or degeneration as the cause of ataxia?
15-9. What symptoms would suggest frontal lobe disease or degeneration as the cause of ataxia?
15-10. Is this gait disturbance real?