Journal of Intellectual Disability Research, 1992, 36, 309-323

Postural stability, tardive dyskinesia and developmental disability Y. G. KO, R. E. A. VAN EMMERIK, R. L. SPRAGUE & K. M. NEWELL Department of Kinesiology, University of Illinois at Urbana-Champaign, Urbana^ Illinois, USA ABSTRACT. The postural stability of four adult populations was examined through force platform methods. The four groups were classified as: (1) dcvelopmentaUy disabled (severely and profoundly mentally retarded) with tardive dyskinesia; (2) developmemally disabled but with no history of neurolepdc medication; ("5) tardive dyskinetic but of normal intelligence; and (4) a normal and healthy control group. Postural conditions included standing still with arms at side, standing still vnth one arm or both arms parallel to the ground, and standing still while sviringing both arms in the sagittal plane. The findings showed that both rardivc dyskineiic and/or developmemally disabled groups exhibited greater sway and variability in centre of pressure motion in contrast lo the control group. TTie developmental disabled with tardive dyskinesia group also exhibited a strong tendency to produce a different form to the postural sway strategy in that they produced rhythmical centre of pressure motions during stance that were, to some degree, task dependent. The findings show that the combined effects of developmental disability and tardive dyskinesia produce qualitatively and quantitatively different features in postural stability panems. TTie data suggest that postural stability measures may be a useful index to assess tardive dyskinesia.

INTRODUCTION A common characteristic of tardive dyskinesia is the display of stereotypic movements in the effector extremities of the body such as toes, feet, fingers, hands, lips and tongue (cf. American Psychiatric Association, 1979; B^lacknik, 1984). These movements are typically viewed to be superfluous patterns of coordination in that they appear unrelated to a specific externally defined action goal. However, these abnormal movements can be so severe as to render some individuals unable to perform functionally on a range of self-help and vocational tasks (Sprague & Newell, 1987). While a number of these stereotypic actions produce movements that are obvious to the eye of the observer, there are also more subtle abnormal features to the movement patterns reflective of tardive dyskinesia (as there are with other movement disorder syndromes). Indeed, these subtle movement properties may be indicative of significant motor control properties of the central nervous system, and moreover, may be used as indices of the onset, current status or ofifset of tardive dyskinesia (Newell & Sprague, 1990). In this paper, the authors report fmdings from an experiment examining the postural stability of individuals Correspondence: K. M. Newell, Department of Kinesiology, University of Illinois at UrbanaChampaign, Louise Freer Hall, 906 South Goodtmn Avenue, Urbana, Illinois 61801, USA. 309

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clinically diagnosed and screened by rating scale methods as having tardive dyskinesia. It was anticipated that the whole-body postural activity of standing upright with as little movement as possible may be a sensitive index of tardive dyskinesia, in much the same way that finger tremor has been used as an index of tardive dyskinesia (May, 1987) and other movement disorder syndromes. The maintenance of posture is a dynamic activity in terms of both the force interactions with the surface of support and the relative motions of the dynamics of body segments (Barin, 1989; Gurfinkel et al, 1971). In this experiment, the authors focused on the forces produced by the body segments at the surface of support through the use of force platform technology {cf. Goldie et al, 1989; Murray et al, 1975). A force platform is an unobtrusive piece of equipment to use with individuals in a clinical or research environment, and it is very sensitive to changes in postural stability as measured by the forces exerted at the base of support. There is usually what appears to be an unstructured pattern to the forces exerted at the feet in normal adult posture (e.g. Sugano et al, 1972; Murray et al, 1975). This same foot force pattern is often exhibited by patients with various movement disorder syndromes although the magnitude of sway and the variability of the forces displayed in the three planes of motion is often times much greater than that exhibited by a normal control group (e.g Diener et al, 1984; Lucy & Hayes, 1985; Mauritz et al, 1979). However, it is possible that the rhythmical stereotypic movements revealed in the effector extremities of individuals diagnosed as having tardive dyskinesia would also appear in postural sway patterns. This could occur either because the rhythmical motion of the peripheral effector stereotype is coupled to the body support segments or because there are independent stereotypic rhythmicities in the postural dynamics. In either case, tardive dyskinesia may be reflected by a different 'form' to the horizontal and vertical components of the centre of pressure patterns than those that support normal upright posture. Although the pattern of the centre of pressure appears unstructured in normal posture there is typically more motion in the anterior-posterior direction than the lateral direction (Goldie et al, 1989), but this trend has been reversed with movement disorder syndromes (Lucy & Hayes, 1985). In this study, four groups of adult subjects were compared to ascertain the influence of both tardive dyskinesia and developmental disability on postural suppon foot forces. Stereotypic movements are evident in individuals diagnosed as having tardive dyskinesia and they also are common in the institutionalized developmentally disabled (Berkson, 1967, 1983; Sprague & Newell, 1987). These abnormal movements are particularly prevalent in the institutionalized developmentally disabled that have also been on prolonged regimes of neuroleptic medication (Baumeister& Forehand, 1973; Lewis & Baumeister, 1982; Sprague & Newell, 1987). An important issue is the possible differences in the movement dynamics of institutionalized stereotypies (Berkson, 1967, 1983) and those stereotypies defined as refiecting tardive dyskinesia (Sprague & Newell, 1987).

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The present authors anticipated that the force platform would be sensitive to detect departures from normal posture both in the form, magnitude and variability of the foot forces produced by individuals diagnosed as having tardive dyskinesia and/or developmental disability.

METHOD Subjects

There were four groups of adult subjects. Tliere were 31 institutionalized individuals (18 males, 14 females) that were diagnosed as developmentally disabled (severely and profoundly mentally retarded) and having tardive dyskinesia. The mean age of this group was 34 years, with a range in age from 23 to 60 years. IQ scores (Mixture of Stanford-Binet and Weschler) were available on all of the individuals tested in this group. The mean IQ was 14-74, with a standard deviation of 4-66. In addition, data from 26 normal healthy individuals from the university community (students and staff) were collected and matched in gender and age (plus or minus 6 months for each subject matched) with the developmentally disabled and tardive dyskinesia group. This normal control group had no history of neuroleptic medication. The mean age of the control group was 33 years, with a range in age from 24 to 59 years. There was also a nondevelopmentally disabled tardive dyskinesia group of nine individuals. The mean age of this group was 53 years and the individuals ranged in age from 38 to 72 years. The fourth group was 32 institutionalized developmentally disabled individuals who were not on medication and had no known history of taking neuroleptic medication. The mean age ofthis group was 36 years with a range in age from 21 to 62 years. Exact IQ scores were not available for this group, but 19 subjects were labelled by the institution as profoundly retarded, eight as severely retarded, four as moderately retarded and one as mildly retarded. The exact medication history of the two tardive dyskinesia groups was not available, which is often the case with individuals from these populations. However, all subjects in both groups had been on neuroleptic medication for some years, and all were diagnosed by their consulting physician as having tardive dyskinesia. The severity of the tardive dyskinesia was also examined by rating scale methods. The tardive dyskinesia of the developmentally disabled group had been diagnosed clinically and evaluated additionally through the use of the DISCUS tardive dyskinesia rating scale (Sprague et al., 1989). The mean DISCUS score of the developmentally disabled with tardive dyskinesia group was 7-75, with a range of 3-0-16-0. Thus, all subjects in this group were determined to have tardive dyskinesia and there was a range of severity of the disorder. The tardive dyskinesia of the subjects of normal intelligence was also determined both by clinical judgement and the DISCUS rating scale. The mean DISCUS score of the group was 8-44, with a range of 2-0-12-0. Thus, all subjects

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in this group were clinically judged to have tardive dyskinesia. The range and mean DISCUS scores of the tardive dyskinesia group of normal intelligence were generally parallel to that of the developmemally disabled with tardive dyskinesia group. Apparatus Postural sway dynamics were recorded with a force platform (Model 0R6-6-1) from Advanced Mechanical Technology, Inc (AMTI).' The force platform simultaneously measures three force components along the x-, y-, and z-axes, and three moment components about these axes. The forces and moments are measured by foil strain gauges attached to load cells at the four comers of the platform. The signals were amplified through an AMTI Model SGA6-4 amplifier (six channel). A maximal gain of 4000 was used with a low-pass filter of 10-5 Hz. Bridge excitation was set to 10 V. All six channels were factory calibrated. The unit of measurement for the three force components (Fx, Fy, Fz) was in Newtons (N), the unit for the three moment components (Mx, My, Mz) was in Newton metres (Nm). Procedures and data analysis

Subjects in all four groups participated in three different experimental tasks. The first task consisted of standing still on the platform with the hands held hanging stationary downwards. In the second task, subjects were asked to hold one (right or left arm separately) or both arms up in front of the body, still and parallel to the ground. Finally, in the arm swinging task, the subjects were asked to swing both arms rhythmically back and forth in the sagittal plane of motion. Instructions to the subjects differed between movement tasks. In the arms down and arms up postural conditions, subjects were instructed to stand as steadily as possible, without moving. In the arm swing condition, subjects were instructed to swing both arms in-phase at their preferred frequency. In case the subject did not understand the instruction (a situation that occurred with a number of developmentally disabled subjects), the required posture or movements were modelled by one of the experimenters. The combination of oral instructions and demonstration was usually enough to get all subjects to perform the respective postural tasks. Some subjects in the two DD groups could not perform the postural tasks and these individuals do not constitute part of the groups discussed here. The data for each trial of each postural task were collected for a duration of 10 s. There were 2 trials for each posture condition that were run consecutively. There was an interval of approximately 15-s between the two trials within a task condition and an interval of approximately 1 min between the different posture conditions. The magnitude and variability in postural sway dynamics were based on the following measures that were derived from the centre of pressure data: (1) the area ^Commercially avaUablefromAMTI, 151 Califomia Street, Newton, MA 02158, USA.

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included within the path of the centre of pressure and the variability of this area; (2) the total length of the path of the centre of pressure and the variability of this length measure; (3) standard deviation of lateral and antero-posterior displacement of centre of pressure (see Goldie et al, 1989, for a review of the relations of these measures). Differences between the population groups and conditions were tested for all dependent variables described above. That is, the sway magnitude and variability measures were compared and contrasted between the developmentally disabled tardive dyskinetic group, the nondevelopmentally disabled tardive dyskinesia group, the developmentally disabled group with no history of neuroleptic medication regimes, and the normal control group. These group comparisons were conducted for all three experimental postural task conditions (arms down, artns up and arms swinging). The force and moment data were collected with a sample frequency of 200 Hz. .\lthough this frequency can be considered high for measurement of postural sway dynamics, this sample frequency was chosen to accommodate accelerometer measurements of the arm motion that were taken synchronously with the force platform measurements. The force platform and accelerometer data were stored on magnetic tape to allow for further processing.

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Task condition Figure 1. Mean length of centre of pressure (cm) as a function of postural task and population group. The postural tasks were: standing still with arms to side (standing still); standing still with left arm up (L. arm up); standing still with right arm up (R. arm up); standing with ieft and right arms up (L. R. arms up); and standing still with left and right arms swinging (L. R. arms swing). The population group conditions were: tardive dyskinesia and developmental disability (TD-DD); developmentally disabled but with no history of neuroleptic medication (DD); tardive dyskinetic but of normal intelligence (TDNDD); and normal, healthy adults (Normal).

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RESULTS The motion of the centre of pressure is one of the primary variables that is derived from the forces and moments measured with the force platform and one of the primary indicators of postural stability (Goldie et ai, 1989). Figure 1 shows the group mean length of path of the centre of pressure as a function of the five postural conditions of standing still with arms to the side, one arm (left or right) parallel to the floor, both arms parallel to the floor, and arms swinging in some preferred mode. These data are based on the mean of two trials for each individual in each group. An ANOVA revealed that the group effect, F (3, 91)=12 80, P

Postural stability, tardive dyskinesia and developmental disability.

The postural stability of four adult populations was examined through force platform methods. The four groups were classified as: (1) developmentally ...
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