Methods

SUBJECTS

Twenty two adult patients between the ages of 17 and 57 (mean age 33.6 (SD 11.8) years) (10 men and 12 women), who met DSM-III-R criteria for OCD, participated in the study. Twenty patients were right handed, the other two patients were left handed (determined by the Edinburgh handedness inventory19). The patients' verbal intelligence was estimated with the Wortschatztest20((WST) mean IQ score 106.9 (SD 11.9)).

All patients gave written consent according to the guidelines found in the Declaration of Helsinki.21 Most of the patients were being treated in the Psychosomatic Hospital Windach at the time of the study. Some of them had been referred to an outpatient clinic specialising in the treatment of OCD and in the long term prophylaxis of affective disorders, localised in the department of psychiatry (Ludwig-Maximilians-Universität (LMU), München). Duration of disease ranged from 1.5 to 30 years (mean duration 10.8 (SD 6.7) years), the patients' mean age at the beginning of disease was 22.2 (SD 10.7) years. The severity of OCD symptoms was assessed using the Yale-Brown obsessive-compulsive scale (Y-BOCS)22 23 and the severity of concomitant depression using the 17 item version of the Hamilton depression rating scale (HDRS)24 and the Beck depression inventory (BDI).25 The patients had a mean total Y-BOCS score of 17.6 (SD 7.9), their Y-BOCS score for obsessions being 9.6 (SD 5.8) and their Y-BOCS score for compulsions 8.1 (SD 5.1). Their mean HDRS score was 17.4 (SD 13.2) and their mean BDI score was 11.5 (SD 7.3). All patients with OCD were medication free for 14 days previous to and during testing; some of them had never received psychotropic drugs. No patient had taken long acting psychotropic drugs known to effect motor control several weeks after termination of treatment (for example, neuroleptic drugs). The patients with OCD had neither focal neurological disease nor any other major medical disorder at the time of testing.

Normal controls (n=22; nine men and 13 women; 21 right handers and one left hander; mean WST score 113.6 (SD 13.8)), with a mean age of 34.9 (SD 13.5) years, were comparable with the patients for sex (χ² (1, n=44)=0.82; p=0.37), handedness (χ²(1, n=44)=0.36; p=0.55), age (t(42)=0.33; p=0.74), and verbal intelligence (WST IQ) (t(42)=1.73; p=0.09). The last two variables were found to have a marked influence on the hand motor performance of healthy subjects.15 The patients with OCD and controls also had comparable occupational profiles, with six patients and 10 controls being pupils or students; five patients and two controls working as secretaries, clerks, etc executing predominantly writing activities; three patients and six controls working in the public health system as physicians, nurses etc; four patients and one control working in commerce (as businessmen, clerks etc); and four patients and three controls predominantly working with coarse motor activities (as workers, housewives etc) (continuity coefficient=0.35; p=0.27). There were also no significant differences between patients with OCD and healthy controls for the mean duration of handwriting per day as reported by the subjects (patients with OCD 69.8 (SD 65.1) minutes per day; controls 55.4 (SD 58.3) minutes per day; Mann-Whitney U=190; p=0.32).

All healthy controls were volunteers recruited by researchers in the department of psychiatry (LMU München) and tested in the laboratory of clinical neurophysiology at that institution. They were free of medication and any DSM-III-R diagnosis of mental disorders. No control had neurological or medical illness at the time of examination.

To test the hypothesis of a lateralisation of hand motor performance in patients with OCD towards the right cerebral hemisphere, we compared the hand motor performance of all right handed patients we had investigated with that of the right handed healthy controls. The groups did not differ significantly in age, sex, verbal intelligence assessed by WST scores, occupational profiles, or mean duration of handwriting per day (in minutes). The mean OCD intensity scores for the right handed patients on the Y-BOCS was 17.1 (SD 7.9), for obsessions 9.3 (SD 5.8) and for compulsions 7.9 (SD 5.1). The average HDRS score for the patients was 10.9 (SD 7.1). The patients' mean age at the onset of disease was 22.7 years (SD 10.6 years); their mean illness duration was 11.2 years (SD 7.0 years).

APPARATUS AND TASK

The subjects first answered a questionnaire to determine relevant characteristics for the analysis of hand movements. Then they filled out the Edinburgh handedness inventory.19 The general level of verbal intelligence was assessed with WST.20

A digitising graphic tablet (WACOM IV), with a sampling rate of maximally 200 Hz and a spatial resolution of 0.05 mm, was used to record the x-y coordinates of the subjects' hand movements. The tablet was connected to a personal computer. The control of trials, the registration of data, and the subsequent signal processing were done with a commercially available program (CS26).

Jahn27 has rigorously tested the above mentioned equipment and software in the analysis of fine motor diadochokinesia in healthy subjects (repetitive drawing of superimposed concentric circles as fast as possible) and found that the internal consistencies of the kinematic CS parameters computed separately for different coordinates and directions were high (r>0.8). Two week stabilities of velocity parameters reflecting diadochokinesia, such as frequency, mean peak velocity, and mean peak acceleration, were found to be in the middle range (0.67<r<0.72). In our own study15 we found 1 week stability values for these parameters to be within a similar range for healthy volunteers (r about 0.6). Higher test-retest reliability coefficients (r>0.7) were calculated for handwriting movement parameters, especially mean peak velocity and acceleration and their variation coefficients.

Hand movement samples were taken in a quiet room of the department of psychiatry of the LMU, Munich, during the day. It was not possible to carry out the investigation at a fixed time because many of the patients with OCD were outpatients and most of the healthy volunteers were not employed at the department of psychiatry. The subjects were seated in an armchair, with an adjustable back, with the digitising tablet in front of them on the top of a desk. Every participant could adjust the chair into a comfortable position. The instructor sat beside the subject, in front of a PC.

The subjects had to carry out the following tasks:

• Firstly they were asked to draw concentric superimposed circles with a diameter of 12 mm between two marked parallel and horizontal lines on a plastic foil to reduce friction, laying over a white sheet of paper (size 29.7×21 cm). They had to perform this task in a natural writing position as fast as possible with their dominant hand for 30 seconds to register their degree of fine motor dysdiadochokinesia. Three segments (5–10 seconds; 15–20 seconds; 25–30 seconds) were analysed and compared to investigate the effects of fatigue on hand motor performance in patients and controls (not reported in this article); the corresponding kinematical variables were then averaged for further statistical analysis.

• To assess hand motor asymmetry, the subjects carried out the same task using their non-dominant hand after performance of some handwriting tasks described below; the same three segments were analysed as above.

• The subjects were also asked to write the given sentence: “Der Ball rollt ins Tor” (“The ball rolls into the goal”) with their dominant hand on a marked horizontal line in about the middle of a white sheet of paper. The subjects were neither asked to write as neatly as possible nor to write as quickly as possible. The instruction was to write as usual in a natural writing position.

• Then the subjects were asked to write their personal signature as usual with their dominant hand on a marked horizontal line on another white sheet of paper; calligraphic aspects or velocity were not specified.

• The third handwriting task was to write the three letters “aaa” with the dominant hand in a row, using cursive handwriting, without raising the ball point pen used for writing. The letter sequences had to be drawn in a relaxed and fluent manner between two parallel horizontal lines on a separate white sheet of paper in four different sizes (6, 12, 18, and 24 mm). The instructor told the subjects that velocity and calligraphy were not relevant in this task.

All subjects wrote and drew with a special ball point pen with magnetic sensors. They received visual feedback on hand movements while writing and drawing. There were no complete practice runs before the test runs, because the tasks were simple. In some cases, the instructor demonstrated the task before recording the subjects' hand movements. The patients with OCD had an opportunity to write and draw superimposed circles on an extra sheet of paper before their corresponding hand movements were recorded. Several patients did so, mostly before the assessment of the degree of their fine motor diadochokinesia. Kinematic variables were only computed for hand movements executed on paper while writing with the dominant hand.

The velocity and acceleration curves for handwriting were computed for the x and y coordinates, but only data for the y coordinate are presented. Kinematic data computed separately for the x and y coordinates have been shown to be equivalent,27 but the data computed for the y coordinate is graphically more illustrative.

In CS, non-parametric kernel estimation was used for the calculation and smoothing of the derivation.28

To determine the different quantitative variables of motion, the coordinates of handwriting movement and its first and second derivations (velocity and acceleration) were divided into time segments, called strokes.

A stroke was defined by the distance between two sequential extreme scores (maxima or minima) of the respective coordinates. These scores corresponded to 0 points of velocity. Similarly, the limits of a segment for velocity were also 0 points of acceleration. These points are identical with the extreme scores of velocity.

For subjects and trials, the following motion parameters were determined: number of changes of direction of velocity (NCV) per stroke; arithmetic mean of stroke peak velocity (mm/s), with the respective variation coefficient (percentage quotient obtained by dividing absolute SD of peak velocity by mean peak velocity—that is, peak velocity inconsistency); mean stroke length (mm) for the given sentence and the personal signature with the respective variation coefficient (stroke length inconsistency), computed only for the handwriting tasks because handwriting size has not been specified; and skewness coefficient (%), the ratio of the acceleration phase to the total movement time.

Movement parameters permit exact statements on the quality of handwriting processing. The number of changes of movement is a measure of the degree of movement automatisation. Highly automatised hand movements, such as skilled handwriting, are represented by bell shaped curves corresponding to monotonous acceleration before and deceleration after the velocity peak of every single stroke within a continuous movement pattern. The number of changes of direction of velocity per stroke is ideally 1.29 Figure 1 illustrates the low degree of handwriting automatisation in a patient with OCD, as reflected by a high number of inversions of his velocity profile (for further characteristics of this patient see ). By contrast, hand movement automatisation in a healthy control performing the same task (drawing of three letter triples (“aaa”) 6 mm high) is characterised by fewer inversions of velocity, or more bell shaped velocity and acceleration curves.

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Figure 1

Temporal segmentation of the amplitude and related velocity and acceleration profiles for a patient with OCD and a healthy control. Both subjects wrote three letters (“aaa”) between two horizontal lines at a distance of 6 mm. The patient needed more time to perform this task than the control (frequency 0.82 Hz; control 2.81 Hz); only the kinematic analyses of his velocity and acceleration profiles show that they are much less regular than those of the control.

To determine the regularity of movement processes, the variation coefficients of kinematic parameters can be used. The ideal score is 0, if the movement replications are identical. Mean peak velocity is suited for the quantification of relative decelerations and accelerations of handwriting movements. Mean peak velocity reflects bradykinesia, the average stroke length micrographia or macrographia, and the skewness coefficient, “the relative proportion of time spent in acceleration during the writing stroke” (Galucciet al 30 p 831). All these parameters were computed by CS.

The results were then statistically analysed with the statistical program SPSS (version 7.5).