Motor Assessments

Introduction

Clinical assessment of movement disorders requires careful visual observation in order to fully characterize the phenomenology and the severity of the disorder. The definitions presented in Chapter 3 and detailed characteristics of individual movement disorders provided in Chapter 7, Chapter 8 and 10–16 rely on descriptions of characteristic spatial and temporal properties of both voluntary and involuntary movements in the specific disorders. Pattern recognition can be helpful, but in many cases, a systematic approach to evaluating specific features is necessary to assure that a correct diagnosis is made. Many movement disorders can be evaluated during the face-to-face clinic visit, but in other cases the movements may not be observed. In those cases, video capture of the movements can be essential for correct diagnosis. The widespread availability of smart phones or tablets with high quality video capability has greatly enhanced the ability of physicians to witness movements and make more accurate diagnoses. Indeed, some movement disorders neurologists are now using telemedicine to evaluate and treat patients with movement disorders. ^,

Although visual assessment of movement patterns by an experienced clinician is sufficient to classify movement disorders, there are limitations. Some patients have more than one movement disorder. Other patients have one or more movement disorders in association with other neurological signs. In these situations, it is usually possible to diagnoses the movement disorders clinically, but it is often difficult to separate out the relative contribution of each to the patient's disability. And sometimes it is difficult to be certain of the correct classification of the movements when they are at the extremes of the characteristic range. For example, very brief choreic movements may resemble myoclonus. The use of technology to measure movements (kinematics), muscle contractions (electromyography), or central nervous system signals associated with individual movements (evoked potentials) may assist in making an accurate diagnosis. These techniques have a utility especially in evaluating functional movement disorders, such as functional myoclonus. Increasingly, remote assessments of movement using wearable technology have been performed in clinical research. Technology has also been used to investigate the pathophysiology of movement disorders in children; those applications will be discussed in chapters on the specific movement disorders.

Beyond diagnosis, there is often a need to assess the severity of the movement disorder in order to gauge disease progression or response to treatment. Although certain technologies can also be used for this, clinical rating scales have greater utility in a routine clinical setting. Several valid and reliable clinical rating scales are available for use in children with movement disorders.

Quantitative Measurement in Movement Disorders

Rating Scales for Pediatric Movement Disorders

Rating scales are clinical instruments that are designed to measure the presence and severity of clinical features. Rating scales can be disease-specific, encompassing many features of the disease. The Movement Disorders Society Unified Parkinson Disease Rating Scale (MDS-UPDRS) and the Unified Huntington Disease Rating Scale (UHDRS) are multidimensional scales that were designed to rate the key features of the relevant disease. One axis for each scale is a “motor” subscale that specifically rates the key features of the movement disorders. These scales have been used widely in clinical studies of Parkinson’s disease and Huntington’s disease in adults. Although these scales were designed to be disease-specific, neither scale is a diagnostic instrument. In other words, a nonzero score on the motor subscale of the MDS-UPDRS does not mean that the patient being evaluated has Parkinson’s disease. Other scales are restricted to a specific sign or symptoms. For example, the Ashworth scale rates spasticity only.

Most published movement disorders rating scales were designed for evaluation of movement disorders in adults. Some of these scales have been applied in studies of children, but their use may be confounded by the impact of development on understanding of instructions and on motor control. ^, Other scales have been developed and tested for use in children.

An ideal clinical rating meets certain criteria including validity, reliability, internal consistency, utility, and responsiveness to treatment. Validity is the ability of a scale to actually measure what it was designed to measure. There are several types of validity. The most common type of validity demonstrated by clinical rating scales is construct (face) validity: does the measure seem reasonable based on what is known of the disorder and is it likely to yield the type of information it was designed to obtain. Convergent validity is the property of performing comparably to a previously validated scale. Discriminative validity is the property of not correlating with a measure of an unrelated variable. Predictive validity is the ability of a scale to predict response to future disease course or response to treatment. Reliability is the degree to which repeated application of the scale within a narrow time window yields the same results. It is a measure of reproducibility. Clinical scales are often evaluated for interrater reliability, agreement between examiners evaluating the same subject, and intrarater reliability, the ability of a single examiner to arrive at the same answer with repeated administration. Internal consistency is the ability of items that should measure the same general construct to produce similar scores. Utility is the ability of a scale to be administered without undue burden to examiner or to subject; can it be used in a routine clinical setting. Responsiveness to treatment is the ability of scale to measure a response to treatment when one exists and to have the sensitivity to determine the minimal clinically meaningful change. Few movement disorders rating scales have met all of these criteria in adults ^, ; even fewer have been shown to have good clinicometric properties in children.

A comprehensive and critical review of movement disorders rating scales for children is beyond the intend scope of this chapter. Many scales designed to assess function, quality of life, care-giver burden, pain, and other aspects of disability or health have been used in studies of movement disorders, but they are not specific to any one particular disorder. In the remainder of this chapter, available scales that are specific to individual movement disorders and that have been used in children with movement disorders will be described under specific movement disorders below. Two unique instruments that were designed to be able to be used in children with more than one movement disorder are discussed at the end of this chapter.