Harrison's Neurology in Clinical Medicine, 3rd Edition

CHAPTER 13. GAIT AND BALANCE DISORDERS

Lewis Sudarsky

PREVALENCE, MORBIDITY, AND MORTALITY

Gait and balance problems are common in the elderly and contribute to the risk of falls and injury. Gait disorders have been described in 15% of individuals older than age 65 years. By age 80 years, one person in four will use a mechanical aid to assist ambulation. Among those 85 and older, the prevalence of gait abnormality approaches 40%. In epidemiologic studies, gait disorders are consistently identified as a major risk factor for falls and injury.

A substantial number of older persons report insecure balance and experience falls and fear of falling. Prospective studies indicate that 30% of those age >65 years fall each year; the proportion is even higher in frail elderly and nursing home patients. Each year, 8% of individuals age >75 years suffer a serious fall-related injury. Hip fractures often result in hospitalization and nursing home admission. For each person who is physically disabled, there are others whose functional independence is constrained by anxiety and fear of falling. Nearly one in five elderly individuals voluntarily limits activity because of fear of falling. With loss of ambulation, there is a diminished quality of life and increased morbidity and mortality rates.

ANATOMY AND PHYSIOLOGY

Upright bipedal gait depends on the successful integration of postural control and locomotion. These functions are widely distributed in the central nervous system. The biomechanics of bipedal walking are complex, and the performance is easily compromised by neurologic deficit at any level. Command and control centers in the brainstem, cerebellum, and forebrain modify the action of spinal pattern generators to promote stepping. While a form of “fictive locomotion” can be elicited from quadrupedal animals after spinal transection, this capacity is limited in primates. Step generation in primates is dependent on locomotor centers in the pontine tegmentum, midbrain, and subthalamic region. Locomotor synergies are executed through the reticular formation and descending pathways in the ventromedial spinal cord. Cerebral control provides a goal and purpose for walking and is involved in avoidance of obstacles and adaptation of locomotor programs to context and terrain.

Postural control requires the maintenance of the center of mass over the base of support through the gait cycle. Unconscious postural adjustments maintain standing balance: long latency responses are measurable in the leg muscles, beginning 110 ms after a perturbation. Forward motion of the center of mass provides propulsive force for stepping, but failure to maintain the center of mass within stability limits results in falls. The anatomic substrate for dynamic balance has not been well defined, but the vestibular nucleus and midline cerebellum contribute to balance control in animals. Human patients with damage to these structures have impaired balance with standing and walking.

Standing balance depends on good-quality sensory information about the position of the body center with respect to the environment, support surface, and gravitational forces. Sensory information for postural control is primarily generated by the visual system, the vestibular system, and by proprioceptive receptors in the muscle spindles and joints. A healthy redundancy of sensory afferent information is generally available, but loss of two of the three pathways is sufficient to compromise standing balance. Balance disorders in older individuals sometimes result from multiple insults in the peripheral sensory systems (e.g., visual loss, vestibular deficit, peripheral neuropathy), critically degrading the quality of afferent information needed for balance stability.

Older patients with cognitive impairment from neurodegenerative diseases appear to be particularly prone to falls and injury. Frailty, muscle weakness, and deconditioning also contribute to the risk. It has been shown that older people who continue walking while talking are at increased risk for falls. There is a growing literature on the use of attentional resources to manage gait and balance. Walking is generally considered to be unconscious and automatic, but the ability to walk while attending a cognitive task (dual-task walking) may be compromised in frail elderly with a history of falls. Older patients with deficits in executive function may have particular difficulty in managing the attentional resources needed for dynamic balance when distracted.

DISORDERS OF GAIT

The heterogeneity of gait disorders observed in clinical practice reflects the large network of neural systems involved in the task. Walking is vulnerable to neurologic disease at every level. Gait disorders have been classified descriptively, based on the abnormal physiology and biomechanics. One problem with this approach is that many failing gaits look fundamentally similar. This overlap reflects common patterns of adaptation to threatened balance stability and declining performance. The gait disorder observed clinically must be viewed as the product of a neurologic deficit and a functional adaptation. Unique features of the failing gait are often overwhelmed by the adaptive response. Some of the common patterns of abnormal gait are summarized next. Gait disorders can also be classified by etiology, as listed in Table 13-1.

TABLE 13-1

ETIOLOGY OF GAIT DISORDERS

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Cautious gait

The term cautious gait is used to describe the patient who walks with an abbreviated stride and lowered center of mass, as if walking on a slippery surface. This disorder is both common and nonspecific. It is, in essence, an adaptation to a perceived postural threat. There may be an associated fear of falling. In one study, this disorder was observed in more than one-third of older patients with a higher level gait disturbance. Physical therapy often improves walking to the degree that follow-up observation may reveal a more specific underlying disorder.

Stiff-legged gait

Spastic gait is characterized by stiffness in the legs, an imbalance of muscle tone, and a tendency to circum-duct and scuff the feet. The disorder reflects compromise of corticospinal command and overactivity of spinal reflexes. The patient may walk on his or her toes. In extreme instances, the legs cross due to increased tone in the adductors. Upper motor neuron signs are present on physical examination. Shoes often reflect an uneven pattern of wear across the outside. The disorder may be cerebral or spinal in origin.

Myelopathy from cervical spondylosis is a common cause of spastic or spastic-ataxic gait. Demyelinating disease and trauma are the leading causes of myelopathy in younger patients. In a chronic progressive myelopathy of unknown cause, workup with laboratory and imaging tests may establish a diagnosis. A family history should suggest hereditary spastic paraplegia (HSP; Chap. 32). Genetic testing is now available for some of the common HSP mutations. Tropical spastic paraparesis related to the retrovirus HTLV-I is endemic in parts of the Caribbean and South America. A structural lesion, such as tumor or spinal vascular malformation, should be excluded with appropriate testing. Spinal cord disorders are discussed in detail in Chap. 35.

With cerebral spasticity, asymmetry is common, involvement of the upper extremities is usually observed, and dysarthria is often an associated feature. Common causes include vascular disease (stroke), multiple sclerosis, and perinatal injury to the nervous system (cerebral palsy).

Other stiff-legged gaits include dystonia (Chap. 48) and stiff-person syndrome. Dystonia is a disorder characterized by sustained muscle contractions, resulting in repetitive twisting movements and abnormal posture. It often has a genetic basis. Dystonic spasms produce plantar flexion and inversion of the feet, sometimes with torsion of the trunk. In autoimmune stiff-person syndrome (Chap. 44), there is exaggerated lordosis of the lumbar spine and overactivation of antagonist muscles, which restricts trunk and lower limb movement and results in a wooden or fixed posture.

Parkinsonism and freezing gait

Parkinson’s disease (Chap. 30) is common, affecting 1% of the population age >55 years. The stooped posture and shuffling gait are characteristic and distinctive features. Patients sometimes accelerate (festinate) with walking or display retropulsion. There may be difficulty with gait initiation (freezing) and a tendency to turn en bloc. Imbalance and falls may develop as the disease progresses over years. Gait freezing is described in 7% of Parkinson’s patients within 2 years of onset and 26% by the end of 5 years. Freezing of gait is even more common in some of the Parkinson’s-related neurodegenerative disorders, such as progressive supranuclear palsy, multiple-system atrophy, and corticobasal degeneration. These patients frequently present with axial stiffness, postural instability, and a shuffling gait while lacking the characteristic pill-rolling tremor of Parkinson’s disease. Falls within the first year suggest the possibility of progressive supranuclear palsy.

Hyperkinetic movement disorders also produce characteristic and recognizable disturbances in gait. In Huntington’s disease (Chap. 29), the unpredictable occurrence of choreic movements gives the gait a dancing quality. Tardive dyskinesia is the cause of many odd, stereotypic gait disorders seen in patients chronically exposed to antipsychotics and other drugs that block the D2 dopamine receptor.

Frontal gait disorder

Frontal gait disorder, sometimes known as “gait apraxia,” is common in the elderly and has a variety of causes. The term is used to describe a shuffling, freezing gait with imbalance and other signs of higher cerebral dysfunction. Typical features include a wide base of support, short stride, shuffling along the floor, and difficulty with starts and turns. Many patients exhibit difficulty with gait initiation, descriptively characterized as the “slipping clutch” syndrome. The term lower body parkinsonism is also used to describe such patients. Strength is generally preserved, and patients are able to make stepping movements when not standing and maintaining balance at the same time. This disorder is best considered a higher level motor control disorder, as opposed to an apraxia (Chap. 18).

The most common cause of frontal gait disorder is vascular disease, particularly subcortical small-vessel disease. Lesions are frequently found in the deep frontal white matter and centrum ovale. Gait disorder may be the salient feature in hypertensive patients with ischemic lesions of the deep hemisphere white matter (Binswanger’s disease). The clinical syndrome includes mental change (variable in degree), dysarthria, pseudo-bulbar affect (emotional disinhibition), increased tone, and hyperreflexia in the lower limbs.

Communicating hydrocephalus in adults also presents with a gait disorder of this type. Other features of the diagnostic triad (mental change, incontinence) may be absent in the initial stages. MRI demonstrates ventricular enlargement, an enlarged flow void about the aqueduct, and a variable degree of periventricular white matter change. A lumbar puncture or dynamic test is necessary to confirm the presence of hydrocephalus.

Cerebellar gait ataxia

Disorders of the cerebellum have a dramatic impact on gait and balance. Cerebellar gait ataxia is characterized by a wide base of support, lateral instability of the trunk, erratic foot placement, and decompensation of balance when attempting to walk tandem. Difficulty maintaining balance when turning is often an early feature. Patients are unable to walk tandem heel to toe, and display truncal sway in narrow-based or tandem stance. They show considerable variation in their tendency to fall in daily life.

Causes of cerebellar ataxia in older patients include stroke, trauma, tumor, and neurodegenerative disease, including multiple-system atrophy (Chaps. 30 and 33) and various forms of hereditary cerebellar degeneration (Chap. 31). A short expansion at the site of the fragile X mutation (fragile X pre-mutation) has been associated with gait ataxia in older men. Alcoholic cerebellar degeneration can be screened by history and often confirmed by MRI. In patients with ataxia, MRI demonstrates the extent and topography of cerebellar atrophy.

Sensory ataxia

As reviewed earlier, balance depends on high-quality afferent information from the visual and the vestibular systems and proprioception. When this information is lost or degraded, balance during locomotion is impaired and instability results. The sensory ataxia of tabetic neurosyphilis is a classic example. The contemporary equivalent is the patient with neuropathy affecting large fibers. Vitamin B12 deficiency is a treatable cause of large-fiber sensory loss in the spinal cord and peripheral nervous system. Joint position and vibration sense are diminished in the lower limbs. The stance in such patients is destabilized by eye closure; they often look down at their feet when walking and do poorly in the dark. Patients have been described with imbalance from bilateral vestibular loss, caused by disease or by exposure to ototoxic drugs. Table 13-2 compares sensory ataxia with cerebellar ataxia and frontal gait disorder. Some frail older patients exhibit a syndrome of imbalance from the combined effect of multiple sensory deficits. Such patients have disturbances in proprioception, vision, and vestibular sense that impair postural support.

TABLE 13-2

FEATURES OF CEREBELLAR ATAXIA, SENSORY ATAXIA, AND FRONTAL GAIT DISORDERS

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Neuromuscular disease

Patients with neuromuscular disease often have an abnormal gait, occasionally as a presenting feature. With distal weakness (peripheral neuropathy) the step height is increased to compensate for footdrop, and the sole of the foot may slap on the floor during weight acceptance. Neuropathy may be associated with a degree of sensory imbalance, as described earlier. Patients with myopathy or muscular dystrophy more typically exhibit proximal weakness. Weakness of the hip girdle may result in a degree of excess pelvic sway during locomotion.

Toxic and metabolic disorders

Alcohol intoxication is the most common cause of acute walking difficulty. Chronic toxicity from medications and metabolic disturbances can impair motor function and gait. Mental status changes may be present, and examination may reveal asterixis or myoclonus. Static equilibrium is disturbed, and such patients are easily thrown off balance. Disequilibrium is particularly evident in patients with chronic renal disease and those with hepatic failure, in whom asterixis may impair postural support. Sedative drugs, especially neuroleptics and long-acting benzodiazepines, affect postural control and increase the risk for falls. These disorders are important to recognize because they are often treatable.

Psychogenic gait disorder

Psychogenic disorders are common in neurologic practice, and the presentation often involves gait. Some patients with extreme anxiety or phobia walk with exaggerated caution with abduction of the arms, as if walking on ice. This inappropriately overcautious gait differs in degree from the gait of the patient who is insecure and making adjustments for imbalance. Depressed patients exhibit primarily slowness, a manifestation of psychomotor retardation, and lack of purpose in their stride. Hysterical gait disorders are among the most spectacular encountered. Odd gyrations of posture with wastage of muscular energy (astasia-abasia), extreme slow motion, and dramatic fluctuations over time may be observed in patients with somatoform disorders and conversion reaction.


APPROACH TO THE

PATIENT Slowly Progressive Disorder of Gait

When reviewing the history, it is helpful to inquire about the onset and progression of disability. Initial awareness of an unsteady gait often follows a fall. Stepwise evolution or sudden progression suggests vascular disease. Gait disorder may be associated with urinary urgency and incontinence, particularly in patients with cervical spine disease or hydrocephalus. It is always important to review the use of alcohol and medications that affect gait and balance. Information on localization derived from the neurologic examination can be helpful to narrow the list of possible diagnoses.

Gait observation provides an immediate sense of the patient’s degree of disability. Characteristic patterns of abnormality are sometimes observed, though failing gaits often look fundamentally similar. Cadence (steps/min), velocity, and stride length can be recorded by timing a patient over a fixed distance. Watching the patient get out of a chair provides a good functional assessment of balance.

Brain imaging studies may be informative in patients with an undiagnosed disorder of gait. MRI is sensitive for cerebral lesions of vascular or demyelinating disease and is a good screening test for occult hydrocephalus. Patients with recurrent falls are at risk for subdural hematoma. Many elderly patients with gait and balance difficulty have white matter abnormalities in the periventricular region and centrum semiovale. While these lesions may be an incidental finding, a substantial burden of white matter disease will ultimately impact cerebral control of locomotion.


DISORDERS OF BALANCE

Balance is the ability to maintain equilibrium: a state in which opposing physical forces cancel. In physiology, this is taken to mean the ability to control the center of mass with respect to gravity and the support surface. In reality, we are not consciously aware of what or where our center of mass is, but everyone, including gymnasts, figure skaters, and platform divers, moves so as to manage it. Imbalance implies a disturbance of equilibrium. Disorders of balance present with difficulty maintaining posture standing and walking and with a subjective sense of disequilibrium, a form of dizziness.

The cerebellum and vestibular system organize anti-gravity responses needed to maintain the upright posture. As reviewed earlier in this chapter, these responses are physiologically complex, and the anatomic representation is not well understood. Failure, resulting in disequilibrium, can occur at several levels: cerebellar, vestibular, somatosensory, and higher level disequilibrium. Patients with hereditary ataxia or alcoholic cerebellar degeneration do not generally complain of dizziness, but balance is visibly impaired. Neurologic examination will reveal a variety of cerebellar signs. Postural compensation may prevent falls early on, but falls inevitably occur with disease progression. The progression of a neurodegenerative ataxia is often measured by the number of years to loss of stable ambulation. Vestibular disorders (Chap. 11) have symptoms and signs in three categories: (1) vertigo, the subjective appreciation or illusion of movement; (2) nystagmus, a vestibulo-oculomotor sign; and (3) poor standing balance, an impairment of vestibulospinal function. Not every patient has all manifestations. Patients with vestibular deficits related to ototoxic drugs may lack vertigo or obvious nystagmus, but balance is impaired on standing and walking, and the patient cannot navigate in the dark. Laboratory testing is available to explore vestibulo-oculomotor and vestibulospinal deficits.

Somatosensory deficits also produce imbalance and falls. There is often a subjective sense of insecure balance and fear of falling. Postural control is compromised by eye closure (Romberg’s sign); these patients also have difficulty navigating in the dark. A dramatic example is the patient with autoimmune subacute sensory neuropathy, sometimes a paraneoplastic disorder (Chap. 44). Compensatory strategies enable such patients to walk in the virtual absence of proprioception, but the task requires active visual monitoring. Patients with higher level disorders of equilibrium have difficulty maintaining balance in daily life and may present with falls. There may be reduced awareness of balance impairment. Classic examples include patients with progressive supranuclear palsy and normal pressure hydrocephalus. Patients on sedating medications are also in this category. In prospective studies, cognitive impairment and the use of sedative medications substantially increase the risk for falls.

FALLS

Falls are common in the elderly; 30% of people older than age 65 years living in the community fall each year. Modest changes in balance function have been described in fit older subjects as a result of normal aging. Subtle deficits in sensory systems, attention, and motor reaction time contribute to the risk, and environmental hazards abound. Epidemiologic studies have identified a number of risk factors for falls, summarized in Table 13-3. A fall is not a neurologic problem, nor reason for referral to a specialist, but there are circumstances in which neurologic evaluation is appropriate. In a classic study, 90% of fall events occurred among 10% of individuals, a group known as recurrent fallers. Some of these are frail older persons with chronic diseases. Recurrent falls sometimes indicate the presence of serious balance impairment. Syncope, seizure, or falls related to loss of consciousness require appropriate evaluation and treatment (Chaps. 10 and 26).

TABLE 13-3

RISK FACTORS FOR FALLS, A META-ANALYSIS: SUMMARY OF SIXTEEN CONTROLLED STUDIES

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The descriptive classification of falls is as difficult as the classification of gait disorders, for many of the same reasons. Postural control systems are widely distributed, and a number of disease-related abnormalities occur. Unlike gait problems that are apparent on observation, falls are rarely observed in the office. The patient and family may have limited information about what triggered the fall. Injuries can complicate the physical examination. While there is no standard nosology of falls, common patterns can be identified.

Slipping, tripping, and “mechanical falls”

Slipping on icy pavement, tripping on obstacles, and falls related to obvious environmental factors are often termed mechanical falls. They occasionally occur in healthy individuals with good balance compensation. Frequent tripping falls raise suspicion about an underlying neurologic deficit. Patients with spasticity, leg weakness, or footdrop experience tripping falls.

Weakness and frailty

Patients who lack strength in antigravity muscles have difficulty rising from a chair, fatigue easily when walking, and have difficulty maintaining their balance after a perturbation. These patients are often unable to get up after a fall and may be on the floor for an hour or more before help arrives. Deconditioning of this sort is often treatable. Resistance strength training can increase muscle mass and leg strength in people in their eighties and nineties.

Drop attacks and collapsing falls

Drop attacks are sudden collapsing falls without loss of consciousness. Patients who collapse from lack of postural tone present a diagnostic challenge. The patient may report that his or her legs just gave out underneath; the family may describe the patient as “collapsing in a heap.” Orthostatic hypotension may be a factor in some such falls. Asterixis or epilepsy may impair postural support. A colloid cyst of the third ventricle can present with intermittent obstruction of the foramen of Monroe, resulting in a drop attack. While collapsing falls are more common in older patients with vascular risk factors, they should not be confused with vertebrobasilar ischemic attacks.

Toppling falls

Some patients maintain tone in antigravity muscles but fall over like a tree trunk, as if postural defenses had disengaged. There may be a consistent direction to such falls. The patient with cerebellar pathology may lean and topple over toward the side of the lesion. Patients with lesions of the vestibular system or its central pathways may experience lateral pulsion and toppling falls. Patients with progressive supranuclear palsy often fall over backward. Falls of this nature occur in patients with advanced Parkinson’s disease once postural instability has developed.

Gait freezing

Another fall pattern in Parkinson’s disease and related disorders is the fall due to freezing of gait. The feet stick to the floor and the center of mass keeps moving, resulting in a disequilibrium from which the patient has difficulty recovering. This sequence of events can result in a forward fall. Gait freezing can also occur as the patient attempts to turn and change direction. Similarly, the patient with Parkinson’s disease and festinating gait may find his feet unable to keep up, resulting in a forward fall.

Falls related to sensory deficit

Patients with somatosensory, visual, or vestibular deficits are prone to falls. These patients have particular difficulty dealing with poor illumination or walking on uneven ground. These patients often express subjective imbalance, apprehension, and fear of falling. Deficits in joint position and vibration sense are apparent on physical examination.


TREATMENT Interventions to Reduce the Risk of Falls and Injury

Efforts should be made to define the etiology of the gait disorder and mechanism of the falls. Standing blood pressure should be recorded. Specific treatment may be possible, once a diagnosis is established. Therapeutic intervention is often recommended for older patients at substantial risk for falls, even if no neurologic disease is identified. A home visit to look for environmental hazards can be helpful. A variety of modifications may be recommended to improve safety, including improved lighting and the installation of grab bars and nonslip surfaces.

Rehabilitation interventions attempt to improve muscle strength and balance stability and to make the patient more resistant to injury. High-intensity resistance strength training with weights and machines is useful to improve muscle mass, even in frail older patients. Improvements are realized in posture and gait, which should translate to reduced risk of falls and injury. Sensory balance training is another approach to improve balance stability. Measurable gains can be achieved in a few weeks of training, and benefits can be maintained over 6 months by a 10- to 20-min home exercise program. This strategy is particularly successful in patients with vestibular and somatosensory balance disorders. The Yale Health and Aging study used a strategy of targeted, multiple risk factor abatement to reduce falls in the elderly. Prescription medications were adjusted, and home-based exercise programs were tailored to the patients’ needs, based on an initial geriatric assessment. The program realized a 44% reduction in falls, compared with a control group of patients who had periodic social visits.