Cervical dystonia severity scale reliability study

Cervical Dystonia Severity Scale Reliability Study

Christopher O’Brien, MD,1,* Allison Brashear, MD,2 Paul Cullis, MD,3 Daniel Truong, MD,4

Eric Molho, MD,5 Stephen Jenkins, MD,6 Joanne Wojcieszek, MD,2 Thomas O’Neil, MD,7

Stewart Factor, MD,5 and Lauren Seeberger, MD1

1Colorado Neurological Institute, Englewood, Colorado, USA2Indiana University School of Medicine, Indianapolis, Indiana, USA

3Wayne State University School of Medicine, Detroit, Michigan, USA4Fountain Valley, California, USA

5Albany Medical College, Albany, New York, USA6Allergan, Inc., Irvine, California, USA

7Macomb Hospital Center, Warren, Michigan, USA

Abstract: Cervical dystonia (CD) is characterized by sus-tained contractions of the neck musculature, resulting in abnor-mal head postures. The Cervical Dystonia Severity Scale(CDSS) was developed to provide a reliable measure of treat-ment response in patients with CD. The CDSS uses a protractorand wall chart to rate the severity of the head’s deviation fromneutral in each of three planes of motion (rotation, laterocollis,anterocollis/retrocollis), which is then scored in 5 degree inter-vals (1 degree to 5 degrees deviation4 1; 86 degree to 90degrees deviation4 18).

To test the reliability of the CDSS, four centers, each withtwo independent examiners, evaluated 42 patients with CD. Ateach site, each of the two examiners used the CDSS to evaluate

the head position of each patient twice, on the same day, for atotal of four evaluations. The kappa value for intra-examineragreement was 0.94 (95% confidence limit of 0.900–0.972),indicating excellent intra-examiner reliability. The kappa valuefor interexaminer reliability was 0.79 for the first evaluationand 0.86 for the second evaluation (95% confidence limits of0.668–0.920 and 0.790–0.920) indicating excellent interexam-iner reliability. Thus, the CDSS was highly reliable in bothintra-examiner and interexaminer scoring comparisons. © 2001Movement Disorder Society.

Key Words: spasmodic torticollis; assessment scale; out-come measure; head position; movement disorder

INTRODUCTIONCervical dystonia, the most common type of focal dys-

tonia,1 is characterized by sustained involuntary contrac-tions of the neck muscles, resulting in twisting and re-petitive movements or abnormal postures of the head.2

Changes in head position include one or more of thefollowing: rotation of the head (torticollis), tilt of thehead in the coronal plane (laterocollis), and flexion orextension of the neck which tilts the head in the sagittalplane (anterocollis or retrocollis). In some patients, lat-eral shift of the cervical spine, sagittal shift of the headand neck, and anterior–posterior shoulder deviation or

shoulder elevation are also present. Because of the vari-ety of movements and postures, which result in part frommuscle contractions, it is very difficult to accuratelymeasure changes in head position in patients with cervi-cal dystonia. However, such measurements are essentialin order to provide a reliable measure of a patient’s re-sponse to treatment.

Measures of cervical dystonia can be defined as ob-jective or subjective. Objective measures rate an exter-nally evaluable impairment resulting from the condition.Subjective measures rate a patient’s internally evaluableimpairment such as pain or disability, (i.e., handicaps,social disadvantages resulting from the impairments, andthe difficulties in performing daily activities). While ob-jective measures are more easily and reliably scored by aphysician in a clinical setting, subjective measures aremore indicative of whether the patient perceives im-

*Correspondence to: Christopher O’Brien, MD, 7475 Lusk Blvd.,San Diego, CA 92121. E-mail: [email protected]

Received 1 December 1999; Revised 11 September 2000; Accepted21 December 2000

Published online 24 November 2001.

Movement DisordersVol. 16, No. 6, 2001, pp. 1086–1090© 2001 Movement Disorder SocietyPublished by Wiley-Liss, Inc.DOI 10.1002/mds.1226

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provement after treatment.3 Ideally, an appropriate as-sessment of cervical dystonia includes both subjectiveand objective scales. However, subjective scales may bedifficult to improve upon without extensive psychomet-ric assessments. Objective scales may be improved interms of ease of use, sensitivity, reliability, and correla-tion with subjective measures.

The most commonly used objective scales are theTsui rating scale4 and the Severity subscale of theToronto Western Spasmodic Torticollis Rating Scale(TWSTRS).5 Both the Tsui scale and TWSTRS severitysubscale estimate the deviation from neutral head posi-tion in broad intervals (15 degrees or 22 degrees), ordescribe the deviation as mild, moderate, etc.4,5 Severalstudies of cervical dystonia patients suggest that thesescales may not be sensitive enough to measure clinicallysignificant changes.3,6–8

The Cervical Dystonia Severity Scale (CDSS) was de-veloped to be a simple, reliable measure of head positionin cervical dystonia patients. The original prototype wasbased on suggestions by one of the authors (D.T.) andsubsequently refined by the other authors. The scale isderived exclusively from objective measurements ofhead position (rotation, laterocollis, anterocollis/retrocollis) in 5 degree intervals using a wall chart andprotractor. It is a simplified and more precise measure ofa single variable, head position, than previously availablescales and, as such, may be useful for routine clinicalassessment of cervical dystonia and response to treat-ment. Furthermore, the CDSS can be used in conjunctionwith rating scales that evaluate other aspects of cervicaldystonia, such as pain and disability, to give an overallassessment of the patient’s status. The present study wasdesigned to evaluate the intra- and interexaminer reli-ability of the CDSS.

PATIENTS AND METHODS

PatientsPatients were included in the study if they gave written

informed consent, were between 21 and 75 years of age,had a clinical diagnosis of cervical dystonia, and wereable to comply with study instructions. Exclusion criteriaincluded pure head shift as the sole component of thecervical dystonia and participation in a clinical trialwithin 30 days of study enrollment.

Study DesignThis was a multicenter study with two examiners at

each of four sites. At each site, each of the two examinersindependently scored each patient twice. Examinersscored each patient’s head position in each direction (ro-tation, laterocollis, anterocollis/retrocollis) using the

CDSS. The order of examiner evaluation was randomlyassigned within each site in blocks of two. Exam 2 fol-lowed exam 1 by 30 to 90 minutes and the order ofexaminer evaluation was reversed.

Cervical Dystonia Severity Scale

The CDSS score was computed as the sum of theseverity scores for head rotation, laterocollis, and antero-collis/retrocollis. The severity score for each of thesedeterminations of head position was obtained with thepatient seated in a chair without head support and withthe thoracic spine in the vertical position. The patientwas instructed to relax with eyes closed, and to allow hisor her head to assume its resting position without the useof sensory tricks (antagonistic maneuvers by patients tocompensate for their abnormal head position) or a neckbrace. The patient was positioned such that the lowercervical spinous process (C7) was aligned with the centerpoint of the wall chart. The protractor was placed parallelto the shoulders.

The patient’s head position was measured in terms ofthe degrees of deviation (from 0 to 90 degrees) fromneutral head position (defined as 0 degree), and the di-rection of the deviation (right or left) when appropriate.Deviations in head position were measured using a pro-tractor (rotation) and wall chart (laterocollis, anterocol-lis, retrocollis) with 5 degree markings (Fig. 1). If headposition could not be accurately measured within one 5degree scoring range, because of a confounding condi-tion such as head tremor, the largest deviation from 0degree was recorded. For rotation, the protractor wasplaced perpendicular to the trunk, flat edge against theshoulders and chin free to rotate above the protractorsurface. When viewed from above, the examiner canthen determine the degree of rotational deviation usingthe subject’s nose or midline of the face as referencepoint. Laterocollis was measured as the tilt of the head,using the vertex as a reference point, in the coronal plane.The vertex was identified by marking the halfway pointbetween the patient’s nasion and inion with a cotton ballattached to the head of the patient. Anterocollis/retrocollis was measured in the sagittal plane, using thevertex as a reference point, with the patient in profile tothe examiner. For consistency, the same patient profile(right or left) was used at every assessment. The devia-tions for head rotation, laterocollis, and anterocollis/retrocollis were each transformed to a severity score(Table 1). The sum of the severity scores for head rota-tion, laterocollis, and anterocollis/retrocollis was the pa-tient’s CDSS score. The possible range of the CDSSscore was from 0 to 54.

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Movement Disorders, Vol. 16, No. 6, 2001

Statistical Analysis

The reliability of the CDSS was assessed by analyzingthe interexaminer and intra-examiner agreement usingthe kappa statistic9 with 95% confidence intervals. UsingFisher’sz transformation10 on an intraclass correlationcoefficient of 0.70 for a sample size of 40, the lower limit

of a 95% confidence interval is 0.54, which is in thefair-to-good agreement range.11

RESULTS

Patients

This study enrolled 42 patients with a diagnosis ofcervical dystonia. The 42 patients were on average age52.5 years (S.D., 11.8; range, 29.6–79.6), average weight77.6 kg (S.D., 17.1; range, 50.3–118.8), and an averageheight of 169.5 cm (S.D., 9.7; range, 150.5–193.7). Pa-tients were predominantly Caucasion (92.9%, 39 of 42),and 57% (24 of 42) were female.

Intra-examiner Reliability

The kappa value for all examiners was 0.94 with alower confidence limit of 0.90, indicating excellent intra-examiner reliability (Table 2). For seven of the eight

FIG. 1. Head position deviation was measured using the protractor andwall chart by seating the patient with the thoracic spine in the verticalposition in a chair without head support and in a relaxed position withthe eyes closed (A); allowing the patient’s head to assume its restingposition without the use of “sensory tricks” (antagonistic maneuvers bypatients to compensate for their abnormal head position) or a neckbrace (B); and (3) measuring degrees of deviation from neutral headposition (0°) in three planes: rotation, laterocollis, and antero/retrocollis(lateral and sagittal shifts not measured), from 1° to 90° (C).

TABLE 1. Cervical dystonia severity scale

Degrees of deviationfrom normal position

Severityscore

0 01–5 16–10 2

11–15 316–20 421–25 526–30 631–35 736–40 841–45 946–50 1051–55 1156–60 1261–65 1366–70 1471–75 1576–80 1681–85 1786–90 18

TABLE 2. Overall intra-examiner reliability

Site Examiner Kappa 95% CI

1 1 0.88 0.786, 0.9722 0.92 0.836, 1.000

2 3 0.94 0.887, 0.9934 0.98 0.958, 1.000

3 5 0.38 −0.121, 0.8886 0.90 0.795, 1.000

4 7 0.87 0.729, 1.0008 0.93 0.843, 1.000

All sitesa 0.94 0.900, 0.972

aAnalysis of the Cervical Dystonia Severity Scale (CDSS) assess-ments made by the one examiner to first evaluate the patient, whereeach patient is evaluated twice by each of two examiners at a site.

CI, confidence interval.

C. O’BRIEN ET AL.1088


examiners, the kappa value ranged from 0.87 to 0.98(lower confidence limits of at least 0.73). For examinerfive, at site three, the kappa was 0.38 with a lower con-fidence limit of −0.12.

Intra-examiner reliability also was examined for eachof the components of the CDSS (Table 3). The range ofthe kappa value was 0.83 to 0.99 for rotation, 0.66 to0.96 for laterocollis, and 0.55 to 0.95 for anterocollis.Because fewer patients had retrocollis, the data were in-sufficient for analysis for three examiners.

Interexaminer Reliability

Across the four sites, the kappa value was 0.79 (lowerconfidence limit, 0.67) for the first evaluation, and 0.86(lower confidence limit, 0.79) for the second evaluation,indicating excellent interexaminer reliability (Table 4).At three of the four sites, the kappa value ranged from0.72 to 0.91 for the first evaluation and from 0.86 to 0.90for the second evaluation. The lower confidence limitsall were greater than 0.52. At site three, the kappa valuewas 0.11 (lower confidence limit, −0.28) and 0.54 (lowerconfidence limit, 0.15) for the first and second set of

evaluations, respectively. The low kappa value at sitethree was consistent with the poor intra-examiner reli-ability for Examiner 5.

Because rotation is the most common deviation in cer-vical dystonia, interexaminer reliability was also ana-lyzed for this component. The kappa scores for rotationalone ranged from 0.68 to 0.96 (Table 5). All examiners,including Examiner 5, showed good agreement on scor-ing rotation.

DISCUSSION

The kappa scores for both intra- and interexaminerreliability indicate that the CDSS is a dependable andreproducible measure of head position in patients withcervical dystonia. By examiner, the kappa values forintra-examiner reliability indicated excellent reliabilityon the composite CDSS score for seven of the eightexaminers. There was no apparent reason for the lowvalue of kappa for Examiner 5, indicating poor intra-examiner reliability. The low value of kappa for thisinvestigator resulted in a low value of kappa for theoverall interexaminer reliability at site three. However, atthe other three study sites, the values of kappa indicatedexcellent interexaminer agreement.

Rotation (torticollis) is the most common componentof cervical dystonia.2,12,13Because rotation is so preva-

TABLE 3. Intra-examiner reliability: Cervical Dystonia Severity Scale(CDSS) components

Site N Examiner Rotation

Kappa

Laterocollis Anterocollis Retrocollis

1 12 1 0.94 0.96 0.86 N/A12 2 0.92 0.87 0.86 N/A

2 9 3 0.99 0.67 0.90 0.789 4 0.99 0.76 N/A 0.99

3 11 5 0.83 0.92 0.55 N/A11 6 0.93 0.91 0.80 0.24

4 10 7 0.92 0.66 0.60 0.8710 8 0.96 0.93 0.95 0.64

All sites 42a All 0.97 0.90 0.88 0.87

aAnalysis of the CDSS assessments made by the one examiner to first evaluate the patient,where each patient is evaluated twice by each of two examiners at a site.

N/A, not applicable; insufficient data for analysis.

TABLE 4. Overall inter-examiner reliability

Site Examiner Evaluation Kappa 95% CI

1 1/2 1 0.72 0.521, 0.9162 0.90 0.855, 0.947

2 3/4 1 0.91 0.805, 1.0002 0.87 0.841, 0.897

3 5/6 1 0.11 −0.284, 0.5002 0.54 0.147, 0.924

4 7/8 1 0.90 0.795, 1.0002 0.86 0.713, 1.000

All sites 1st/2nd 1 0.79 0.668, 0.9202 0.86 0.790, 0.920


TABLE 5. Interexaminer reliability for rotation

Site n Examiner Kappa 95% CI

1 12 1/2 0.88 0.743, 1.0002 9 3/4 0.96 0.930, 0.9923 11 5/6 0.68 0.346, 1.0004 10 7/8 0.94 0.870, 1.000

All sites 42 1st/2nd 0.93 0.883, 0.983


CDSS RELIABILITY STUDY 1089


lent, it is particularly important that the scale demon-strate reliability for this component. Excellent reliabilitywas seen for all eight examiners in measuring rotation.The examiner with the least reliability on the CDSS com-posite score still had a relatively high kappa value forscoring rotation.

In this study, the reliability scores for rotation mea-sures were higher than the reliability scores for latero-collis or anterocollis/retrocollis measures. In part, thismay be because rotation is more common in cervicaldystonia patients, and evaluators have had more experi-ence assessing rotation. In addition, rotation measure-ments are not altered by shoulder deviation (as the pro-tractor is placed against the shoulders) but are perpen-dicular to the trunk and are altered only to a small extentby lateral shift. In contrast, laterocollis measures are al-tered by any thoracic scoliosis or shoulder deviation.These variables were not assessed in this study. Finally,the inion was not easily identified in some patients, lead-ing to some variability in defining the vertex for mea-sures of laterocollis and anterocollis/retrocollis.

The present study supports the reliability of the CDSSas a measure of head position in patients with CDSS.However, it does not address whether the measure isclinically meaningful. In a preliminary study,14 theCDSS correlated well (P < .001) with the physician’sGlobal Assessment score, a general measure of improve-ment of the symptoms of cervical dystonia, after treat-ment with botulinum toxin A. This indicates that theCDSS may also act as an indicator of clinically relevantchanges after treatment. Further studies are needed todetermine whether changes in the CDSS are indicative offunctional changes in cervical dystonia patients aftertreatment.

Unlike other rating scales of cervical dystonia, theCDSS is based on objective, precise (to 5 degrees), andreproducible measurements of head position rather thanthe broad-range estimates (e.g., 15 or 22 degrees) ofother scales.4,5 The CDSS provides a simplified measureof head position. This has the advantage of decreasingthe number of variables involved in the assessment ofCD, making the measurements easier to reproduce. How-ever, it also has the limitation of not including otherpotentially objective aspects of cervical dystonia such asthe effect of sensory tricks, duration of head deviation,and shoulder elevation. Although considered in the pre-liminary CDSS design, additional measurements werefelt to detract from the goal of relative simplicity. Vari-ables such as pain and quality of life are important sub-jective parameters in assessing cervical dystonia, buttheir inclusion in an objective rating scale may decrease

the reliability of the scale. The CDSS can be used inconjunction with these specific measures to give an over-all assessment of the patient’s status and capture lessobjective treatment effects. Indeed, the use of additionalsensitive subscales may help us to better understand pa-tient characteristics and their response to treatment.

Unlike the TWSTRS or Tsui scales, the CDSS re-quires instrumentation, a protractor and wall chart, whichmakes the scale less portable. We have found, however,that permanent placement in the exam room providessimple access for day-to-day use in the clinic.

In summary, the CDSS provides a reliable measure ofthe severity of head position deviations in patients withcervical dystonia. This scale may prove to be a usefulclinical tool for the assessment of cervical dystonia.

Acknowledgments: We thank Jan Chrzan, RN (Waxman,MI), for her assistance in this study. This work was supportedby Allergan, Inc. (Irvine, CA). E.S.M. was also supported bythe Riley Family Chair in Parkinson’s Disease, Albany MedicalCollege (Albany, NY).

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Cervical dystonia severity scale reliability study