CHAPTER 5

Measurement Tools and Treatment Outcomes in Patients With Spasticity

Elie Elovic

Numerous forces have changed the face of rehabilitation over the last decade. Some of them include a greater emphasis on evidence-based medicine, tighter control of medical services by payers, and a greater importance being placed on functional outcome metrics. Pierson (1,2) stated that the driving force behind the development of objective measurements is pressure from the academic medical centers and the insurance companies. As a result, objective and functional measures are being used to evaluate the efficacy of spasticity interventions. Past assessment efforts have focused on specific impairments (eg, range of motion [ROM], tone- and velocity-dependent resistance to passive stretch) and they have been used widely in the spasticity literature. The correlation between improvements in these parameters and overall function has not been well documented and there is a need to further explore means of assessing outcomes to further develop research and clinical assessment. While objective information is important, the correlation with functional improvements remains critical. As was stated so eloquently by Taricco et al (3) in their Cochrane Database Review, “No matter how difficult these latter measurements could be, evidence based clinical practice should be primarily based on patient oriented outcomes.”

SPASTICITY OUTCOME MEASURES—WHAT IS A USEFUL OUTCOME MEASURE?

Spasticity is a derivative of the Greek word “spasticus,” which means to pull (4). Young defined spasticity as a velocity-dependent hyperreflexia (5), while the definition most often quoted is by Lance (6), “A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon reflexes, resulting from excitability of the stretch reflex.”

The next question is what is meant by the term outcome. A text, written by Finch et al (7), was dedicated to the subject of rehabilitation outcome assessment. They described it as “a characteristic or construct that is expected to change owing to the strategy, intervention or program.” The authors gave the reader further useful advice when they gave recommendations regarding the choice of an appropriate outcome metric. They suggested that one should choose a measure that is likely to be sensitive to the changes that may occur as a result of the intervention. In addition to clinical skills, awareness of the potential positive and negative results from an intervention and a keen awareness of the patient and his or her clinical situation is required to appropriately choose an outcome measure. Ideally, an outcome measure should facilitate clinicians’ efforts in the determination of condition severity and treatment efficacy. Using an appropriate metric to assess treatment efficacy is critical to logically decide when to modify a treatment protocol or when to stop treatment.

What is a useful outcome measure? To some extent it depends on the prospective of the observer. For many clinicians and rehabilitation scientists, intra- and interrater reliability are critical. Ideally, a measure should be objective as subjective ones may depend on the skill set of the rater and certainly may reflect the examiner’s bias. For scientific purposes, objective metrics have a clear advantage over subjective ones. For the insurance companies, significant functional changes, level of care required, and pharmacoeconomic matters may be the most important. For the patient and family, function and the demands on caregivers are essential. Although clinicians may be happy with reduced tone and increased ROM, the patient may be pleased if an arm is easier to wash and move passively, even if no active function is recovered from an intervention. This issue will become even more important as the cost of health care is debated. Is reducing perceived tightness in a hand without active or passive function worth injections with botulinum toxin four times a year? This question is not one that has to be answered by clinicians but more likely will be answered by society, insurance, and government bodies.

AN ORGANIZED APPROACH TO SPASTICITY OUTCOMES

To fully understand the different metrics that can be used to evaluate spasticity outcomes it is important to organize the material to facilitate understanding. The first categorization of outcome metrics is whether they are subjective or objective. The Ashworth Scale used to assess tone or the Disability Assessment Scale are examples of subjective measures as the judgment of the evaluators plays an important part in the assignment of scores. This is true despite the fact that intra- and interrater reliability has been demonstrated with both of these metrics. On the other hand, the measurement of ROM around a joint or the 6-Minute Walk Test are examples of objective measures. Another way to divide the means of outcome assessments is to group them by what they measure. Revising earlier work performed by the authors (8), they are proposing six separate categories of metrics in a hierarchical progression to stratify outcome goals from spasticity interventions. They are physiological measurements (ratio of maximum H reflex to maximum M response [H/M] ratios); measures of passive activity (eg, Ashworth Scale and passive ROM); measures of voluntary activity (ie, Fugl-Meyer, 9-Hole Peg Test); measurements of passive (ability to don a shirt) and active function (25-foot walk); and quality of life (QOL) measures (short form [SF]-36 health survey). Clinicians treating the patients can set goals at multiple levels. Ideally, addressing goals at the highest level would be the most desirable but a patient’s clinical presentation may require that the bar be set lower initially.

At the lower end of the spectrum, specific musculoskeletal and physiological measures are evaluated, while at the higher end, function, performance of volitional tasks and how a person perceives his or her life is evaluated. Patients do not often present to a clinician’s office asking for changes based solely on achieving changes in physiological measures. Their desires often reflect improvement in their ability to interact and function within the world. Although initially clinicians must often set short-term goals that are more limited in scope, ultimately when possible it is important that the issue of function be addressed. As Finch et al (7) stated, “While rehabilitation efforts target many different substrates that include impairments, activity limitation, and decreased participation, outcome assessment efforts should be directed at an individual’s ability to be active and to participate in life as he/she wishes.”

It is problematic for clinicians and researchers to measure changes in function and QOL in people who are undergoing treatment for spasticity. Although there are many reasons for this, some of the more common ones are the heterogeneity of the population served, other impairments that are often associated with spasticity (eg, weakness, incoordination, and sensory deficits) that complicate function, and finally “fixing” muscle overactivity may not directly result in improved QOL. Elovic et al (9) was one of the first groups that were able to demonstrate improvements in QOL with repeated open label injections of botulinum neurotoxin in the upper extremity in people with upper extremity spasticity secondary to stroke. However, much further work needs to be done.

PHYSIOLOGICAL MEASURES

When one uses the term “physiological outcome measure” it often refers to electrophysiological information that has been correlated with muscle overactivity. Some examples of these include measuring the excitability of the motor neuronal pool or measuring the decrease in length that is seen in muscle cells when spasticity is evident (10). Other items that have been used as outcome metrics include the vibratory inhibitory reflex and the H_max/M_max ratio as they have been noted to be abnormal in people with spasticity. Stokic and Yablon (11) have evaluated the efficacy of intrathecal baclofen and its relationship to the H reflex. The fact remains that while these findings may be true, they are at best correlated with spasticity and at this time have not yet been shown to be directly related to function. One fact that is in favor of physiological assessments is that the data collected are objective in nature, which is different than many of the measures commonly used by rehabilitation professionals. It is possible that these measures will be of benefit to researchers and assist both clinicians and researchers in understanding the pathophysiology of muscle overactivity.

Measures of Passive Activity

For this category of assessment metrics, few things are asked from the person being examined except possibly to relax. It is the clinician or researcher who performs the activity. Some examples of this work include evaluating resistance to movement using a scale such as the Ashworth Scale or Tardieu Scale if a velocity component to stretch resistance is assessed. Biomechanical devices where torque is applied and measured also fall into this category. Metrics such as the Ashworth and Tardieu Scales are somewhat subjective in nature while some of the torque measurement devices give more objective feedback.

Measures of Voluntary Activity

The assessment metrics in this group differ from the previous one because they involve measurements taken while the person is actively involved. These measures are not actually addressing real-life functional tasks. Examples of this include items such as 9-Hole Peg Test or the Fugl-Meyer. These tests evaluate motor function and may well be correlated to real-life function, but they are not real-life tasks by themselves. Another example is pedobarography (measurement of foot pressures during weight-bearing activities). This could be accomplished while the person is measured during a timed walking task. The velocity of walking is a true active functional measure; however, the pressures on the foot are not functional themselves. When gait analysis is performed, measures of both true function and voluntary activity (kinematics, pressures, electromyography [EMG] cycle) are often collected simultaneously.

Passive and Active Function

In the rehabilitation environment, function is commonly defined as one’s ability to perform important activities such as hygiene, walking, or dressing. Commonly used scales include the Functional Independence Measure and the Berg Balance Scale, which can be somewhat subjective in nature. The timed 25-foot and 6-Minute Walk are more objective functional measures that are assessed commonly in the neurologic population. After a neurologic event, the word “function” is often further subdivided into passive and active functional tasks. Examples of passive function include the ability to perform hygiene in the hand that can be complicated by muscle overactivity or the ability to perform a straight catheterization that is complicated by adductor spasticity. The difference between active and passive function is that in the passive arena, something is done to the area versus active movement of the area being assessed.

QOL MEASURES

Ideally as clinicians, one would like to intervene and improve the QOL for the people we treat as that would imply that our efforts improve our patients’ satisfaction with life. However, this task can be somewhat challenging as improving muscle overactivity may be inadequate to accomplish this as so many factors affect QOL in the populations with spasticity. Elovic et al (9) were able to demonstrate that repeated injections with neurotoxin did make a statistical difference in QOL in people with stroke-related spasticity. This study was limited by its open label design but should give clinicians and researchers some hope for the future.

CHOOSING AN OUTCOME MEASURE TO ASSESS INTERVENTION EFFECTIVENESS

How does one choose an appropriate outcome metric to assess clinical efficacy? This may be a challenging exercise as one must pick a metric that is relevant to the intervention being provided and at minimum correlates with a desirable outcome. Taricco et al (3) called for “more clinically relevant measures of treatment effects to be able to realistically assess clinically relevant end points dealing with functional recovery.” This statement was a result of the fact that after they performed a comprehensive review of the medication interventions for the management of muscle overactivity, they found a paucity of functional metrics being reported. The Disability Assessment Scale that was originally introduced in 2002 (12,13) is an attempt to develop subjective measures of functional improvement/reduced impairment. Rehabilitation scientists are also working to objectify and investigate the changes and relationships in motor impairment, disability, and real-life function (14–16). Engineering solutions have also been developed that can address the issues of developing objective quantifiable outcome metrics (17,18).

As there are differences in every patient’s presentation, condition, current level of functioning, diagnosis, pathophysiology, comorbidities, and residual function, it is hard to predict with 100% accuracy what changes will be noted after an intervention. However, the outcome and therefore the choice of appropriate metrics are clearly a product of the factors mentioned earlier and the modality/modalities that are being used for treatment. Evaluations must be performed by skilled clinicians and goal setting should be reality based. A single intervention can demonstrate changes at multiple levels depending on the patient being treated.

A good example of this issue is the management of hip adductor spasticity. This condition can be a result of numerous etiologies and can manifest itself very differently depending on the clinical presentation. In some very severe cases of multiple sclerosis-related spasticity, the patient is bed ridden and the entire purpose for intervening is to improve hygiene and ability to perform straight catherization, while in other patients the muscle overactivity results in a narrow-based gait and the reason to treat is to improve ambulation. While increased ROM and decreased tone can be goals in both cases, in the former, the goals at the highest level are primarily a passive functional one while in the latter, gait speed and stability may be the active functional goal that is strived for.

TYPES OF ASSESSMENT METHODS AND TOOLS

Up to this point the authors have discussed the categories in general. They will now turn their attention to the individual outcome assessment metrics. In Table 5.1, many of the metrics that are commonly used in the assessment of spasticity are listed, along with their classification as proposed by the authors and whether they are subjective or objective in nature.

TABLE 5.1

^a In some cases this could reflect passive function as improvement could result from ease of passive activity performed (ie, ease of hygiene secondary to reduced muscle overactivity).

Physiological Measures

Measures Using Nerve Conductions. Electrophysiological measures have often been used in the assessment of spasticity. In particular, the Hmax, the ratio of the Hmax/Mmax, F response, and vibratory inhibition of the H reflex have been used by investigators as metrics evaluating spasticity (17). The H reflex is elicited by a stimulation of the sciatic nerve at gradually increasing frequencies at a relatively low current, which stimulates the Ia sensory fibers that then antidromically stimulate some of the motor neurons. It appears with an approximately 30-ms time delay. As one increases the strength of the stimulation, the H reflex disappears and the M wave that reflects the activity of the total pool of motor neurons firing appears. The H reflex is mediated through the Ia sensory fiber and because these fibers have increased activity when spasticity is present, it is increased when muscle overactivity is present. As a result of this fact the ratio of Hmax/Mmax reflects the physiology that is seen in spasticity. The M response reflects the total pool of motor neurons that can be excited by stimulation while the H response instead reflects only the motor neurons that can be excited by antidromic stimulation mediated through the Ia fibers (17). As the excitability of the Ia fibers is intimately involved with spasticity, the ratio of Hmax/Mmax measures the underlying physiology associated with spasticity (17,19–21). The ratio ranges between 5% and 35% in normal individuals and is higher when spasticity is present (22,23). It has been used frequently in various populations by authors quantifying spasticity (24–27) as well as a component for the evaluation of treatment efficacy (28–32). The readers are cautioned that this is not a true measure of spasticity but instead it is an electrophysiological correlate, which is not diagnostic by itself.

Another electrophysiological measure that results from antidromic stimulation of the motor neuron is the F-wave. Similar to the H reflex it has also been shown to be increased when spasticity is present or there is hyperexcitability of the motor neuronal pool (17,33–35). A change in the amplitude of the F wave has been used as a potential outcome metric for different treatments of spasticity in different patient populations. Again the caution mentioned earlier regarding the clinical relevance of these electrophysiological metrics must be noted. In fact, Pauri et al (36) demonstrated that, although patients treated with botulinum toxin demonstrated clinical changes, there was not a comparable change in these electrophysiological measures.

Vibration reduces the H reflex and the classic measure used to evaluate this is the Vibratory Inhibitory Index, which is standardized to be applied at 100 Hz to the Achilles tendon, which then in turn inhibits the H reflex (17,37,38). In young normal patients, the vibration reduces the H_max to roughly 40% of the nonvibratory state; however, it is elevated in patients with spastic hemiplegia (39). Investigators have shown that inhibitive casting lowers this ratio (40).

Tendon Reflex. In order to obtain quantitative information regarding reflex activity it is necessary to be able to apply reproducible and measurable stress, stretch, and perturbations to muscles and tendons. Advances in technology have enabled researchers to perform these actions to obtain a better understanding of the stretch reflex and joint mechanics. As a result, reflex gain and threshold have been explored. Gain is defined as the slope of the stretch reflex amplitude plotted against angular velocity, while the threshold is defined as the angular velocity when the stretch reflex is first evoked. When compared to normal controls, people with spasticity have a much steeper slope of the stretch reflex amplitude and a much lower threshold (41). Reinkensmeyer et al (42) created a device to assess and treat a person’s arm after neurologic injury. It assesses one’s muscle overactivity and is also a therapeutic device. Its mechanism for assessment is to measure a reflex response after the application of small perturbation. Potentially, this device could also be effective in monitoring response to treatment.

Reflex excitability can be estimated by a series of devices that tap the tendon and elicit reflex activity at the knee. When the stimulus is applied, reflex torque is measured and EMG activity is recorded from the soleus, gastrocnemius, and tibialis anterior. One group (43) mounted a force sensor on either the patellar or Achilles tendon to measure both the stimulation tap and subsequent response. Further work by these scientists in a sample of people with multiple sclerosis-related quadriceps increased tone, noted a decreased tapping threshold necessary to elicit a response, and an increased torque that was related to increased spasticity (44). These types of devices have the ability to objectify and quantify hyperreflexia. It is worth noting that increased reflexes are often related to spasticity but can be separate constructs that can be found either together or by themselves (45).

Measures of Passive Activity

This group of metrics consists of measurements that are performed on the person who remains passive throughout while spasticity is being assessed. These include passive ROM, the assessment of muscle tone (Ashworth Scale), or spasticity (Tardieu) as examples. In an engineering sense this includes the assessment of torque, stiffness, and viscosity. The latter groups of assessment are often used as quantifiable correlates of common clinical measures.

Ashworth, Modified Ashworth, and Modified Modified Ashworth Scales. Despite enormous criticism, the vast majority of spasticity papers have used either Ashworth or Modified Ashworth Scales (MAS) as a primary or secondary outcome metric. First published in 1964 (46), the Ashworth Scale is probably the most universally recognized metric (1,2). Subjectively, the examiner assigns a score ranging from a 0 to 4 value based on the amount of increased resistance that he or she perceives while passively moving the person’s joint through its available ROM. As seen in Table 5.2, the scores range from 0 when no increased tone is perceived to a level of 4 when the limb is rigid (46). For the upper extremity stroke patient, Brashear et al (13) demonstrated that there was good intra- and interrater reliability in the assessment of spasticity at the wrist, fingers, and elbows. However, its utility and reliability in the lower extremity are more questionable. A group that studied the Ashworth Scale for plantar flexor tone secondary to traumatic brain injury (TBI) classified it as “minimally adequate” because of marginal intra- and interrater reliability (47). A similar study evaluated the Ashworth in plantar flexors of patients with stroke (48). They found questionable interrater reliability, with the best correlation noted with the score of 0.

TABLE 5.2

The Modified Ashworth Scale (Table 5.3) was proposed by Bohannon and Smith (49). In an attempt to strengthen the original Ashworth Scale they added a 1+ measure, differentiating in from a 1 by the presence or absence of increased tone after the initial catch was appreciated. The authors reported that for elbow flexor tone secondary to acquired brain injury there was good interrater reliability. Ansari et al raise further questions regarding the interrater reliability of both the Ashworth and Modified Ashworth Scales (50). Instead, they propose the Modified Modified Ashworth Scale (Table 5.4), which they report has good or better interrater reliability in both the elbow and wrist (51,52).

In summary, the Ashworth and its cousin the Modified Ashworth are well known and easy to perform and have a long history of use in clinical trials and practice. Their effectiveness as metrics have always been questionable. The place for the new Modified Ashworth Scale is not yet known and further studies will hopefully answer these questions. Clinicians and scientist should be aware of the strengths and weaknesses of these measures.

TABLE 5.3

TABLE 5.4

Tardieu Scale. The Tardieu Scale has been suggested as a suitable and reliable alternative to the Ashworth for the use in the measurement of muscle spasticity (53–55). It was first published in 1954 (56) and has an advantage over the Ashworth group of metrics as it truly incorporates velocity into the assessment. Although first published in 1954, it has undergone two modifications. The first was by Held and Pierrot-Deseilligny in 1969 (57) and a further update, the Modified Tardieu Scale, was published in 1999. Items addressed by the scale include intensity of the resistance to muscle stretch, the angle at which the catch is first noticed, the presence of clonus (fatigable vs nonfatigable), and the differences noted when a muscle is ranged at different velocities (Table 5.5).

TABLE 5.5

Gracies demonstrated its ability to assess spasticity, its reliability, and its potential to document changes secondary to interventions (58). There are certainly potential problems with the scale, including its reliance on clonus, which may make it difficult to interpret at the higher ends of tone. In addition, clonus can worsen as a person’s ROM increases after an intervention and as a result, while there may be clinical improvement, the Tardieu Score could worsen (8). The literature regarding the reliability of the Modified Tardieu Scale has been mixed and there are studies that show both good (59) and poor (60) intra- and interrater reliability. Ansari showed that the use of inexperienced raters also contributed to poor interrater reliability (61).

In summary, the Tardieu and Modified Tardieu Scales are more recently being used in spasticity studies and evaluators should be aware of these instruments. However, it is essential to reiterate that there is no concrete evidence demonstrating that is clinically superior to the Ashworth Scale. In addition, there is has been no correlation demonstrated between changes on the Tardieu Scale and functional activity.

Range of Motion

ROM measurements have been used as an outcome measure for spasticity intervention for many years. They are ubiquitous as they are relatively easy to perform. The information can be obtained manually using a goniometer and brute strength for a tight ankle or by using electrogoniometry (the electrical measurement of joint angles), which can deliver more accurate and precise measurements. The technology needed for electrogoniometry can be accomplished using precision rotary potentiometers, Rotary Variable Differential Transformers (RVDTs), flexible strain gauges, and noncontact magnetic and capacitive technologies (17). ROM is often measured along with the stretch reflex using the same assessment device. Three-dimensional (3D) motion analysis can capture ROM kinematics during functional task performance (62). There are potential problems with these devices and it is critical that torque remain uniform for these devices to be accurate (63). There remains the continuing problem regarding functional significance. Changes in function were not always seen when there were changes in MAS and ROM brought about by spasticity intervention (64).

Stiffness and Muscle Tone. With the desire to obtain objective data regarding the assessment of muscle tone it is natural that engineers and scientists addressed this with technological advances. These devices can measure stiffness, muscle tone, and reflex activity and provide quantitative data related to the qualitative information obtained from the subjective assessment of tone. In addition, a properly maintained device can eliminate the issues of test/retest variability and interrater differences that plague the Ashworth. These devices can measure torque, angular velocity, and EMG simultaneously. Torque is defined as force that tends to produce a rotation and is the product of force times distance. Torque is the tendency of a force to rotate an object around an axis, and is produced when a force is applied at a distance from the point of rotation. Many authors and researchers have advocated the use of the torque versus angle relationship at a joint as the most appropriate assessment of spasticity based on its similarity to the clinical quantitative assessments and definition of spasticity. The most common outcome measure for comparisons and correlations has been the MAS (18,65–68). However, a change in muscle tone from a spasticity intervention does not necessarily correspond to functional improvement.

Stretch and Stretch Reflexes. The observed behaviors of spasticity and hyperreflexia are actually a result of a combination of the intrinsic mechanical properties of the soft tissue and the reflex activity itself. By varying the rates at which a joint is stretched, investigators have made progress into studying these parameters separately. When a joint is stretched at a relatively slow rate of between 2°/s and 12°/s, the effects of limb inertia are relatively minor and an assessment of the nonneurologic components of tone and stiffness can be obtained. However, when a joint is put at stretch at a much higher rate (>14–35°/s), the stretch reflexes are initiated and can be assessed (69,70).

Engineers developed a portable device that measured angular velocity around the knee that resulted from a force applied to the ankle (71). When using the device, the evaluator flexes and extends the knee at different speeds. While this is being performed, plots of the force–angle–velocity are recorded. Spasticity was quantified as a regression slope of the linear fit to the peak force/angular velocity data.

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