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Keywords:

  • Juvenile idiopathic inflammatory myopathies;
  • Juvenile dermatomyositis;
  • Muscle strength assessment;
  • Physical function

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Objective

To document and evaluate the scores that normal, healthy children achieve when performing 9 maneuvers of the Childhood Myositis Assessment Scale (CMAS).

Methods

A total of 303 healthy children, 4–9 years of age, were scored as they performed 9 CMAS maneuvers. The data were then evaluated to determine whether normal scores for some maneuvers are age and sex dependent.

Results

All children were able to achieve maximum possible scores for the supine to prone, supine to sit, floor sit, floor rise, and chair rise maneuvers. All but 2 4-year-olds achieved a maximum possible score for the arm raise/duration maneuver. Performance of the head lift and sit-up maneuvers varied significantly, depending primarily on age. Children in all age groups had less difficulty performing the leg lift than the head lift or sit-up.

Conclusion

The normative data generated by this study are of value for interpreting the serial CMAS scores of children with idiopathic inflammatory myopathies.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The juvenile idiopathic inflammatory myopathies (juvenile IIM) include juvenile dermatomyositis, juvenile polymyositis, overlap myositis (myositis associated with other connective tissue diseases such as lupus and mixed connective tissue disease), and other rarer myositis subsets (1, 2). The most common of the juvenile IIM is juvenile dermatomyositis (3).

The dominant clinical feature of juvenile IIM is chronic proximal and axial muscle weakness. This weakness tends to progress without treatment and usually responds to corticosteroid therapy, although not always adequately. Many patients require additional immunosuppressive therapies.

One of the most important aspects of disease management is serial testing of muscle strength and physical function. Serial use of a standardized, quantitative muscle assessment instrument enables the clinician (and clinical researcher) to longitudinally document the progress of an individual patient. These quantitative measurements play an essential role in guiding treatment and studying the efficacy of various therapies.

The Juvenile Dermatomyositis Disease Activity Collaborative Study Group has developed and validated such an instrument—the Childhood Myositis Assessment Scale (CMAS)—a quantitative, observational, performance-based instrument for composite assessment of muscle function, strength, and endurance in children with juvenile IIM (4). The CMAS was developed to complement manual muscle testing, which may be difficult to administer and accurately interpret in young children.

The CMAS consists of 14 physical maneuvers that children with inflammatory myopathies are asked to perform at serial clinic visits (Table 1). A full description of the CMAS is provided on the American College of Rheumatology Web site (URL: www.rheumatology.org). This official version of the CMAS differs from that originally published (4) due to misprints (in the original) regarding items 4, 8, and 12. The 14 maneuvers primarily assess proximal and axial muscle groups. For each maneuver, patients are awarded “points of muscle strength” depending on which standardized descriptor best fit their performance of the maneuver. The maximum possible total score for the 14 maneuvers is 52 points. The CMAS has been demonstrated to have excellent convergent validity and excellent inter- and intrarater reliability (4, 5).

Table 1. Nine CMAS maneuvers tested*
CMAS maneuversMaximum possible score for each maneuver
CMAS-14CMAS-9CMAS-9CMAS-14
  • *

    CMAS = Childhood Myositis Assessment Scale.

1. Head liftHead lift55
2. Leg raise/touch object  2
3. Leg lift/durationLeg lift/duration55
4. Supine to proneSupine to prone33
5. Sit-upsSit-ups66
6. Supine to sitSupine to sit33
7. Arm raise/straighten  3
8. Arm raise/durationArm raise/duration44
9. Floor sitFloor sit33
10. All fours maneuver  4
11. Floor riseFloor rise44
12. Chair riseChair rise44
13. Stool step  3
14. Pick-up  3
Total 3752

The CMAS is primarily designed to serially compare an individual patient's current performance with his or her past performances. Serial CMAS scores may then be plotted to depict that patient's clinical course. Because the patient serves as his or her own control, comparison of the patient's CMAS scores with that of healthy children is not necessary to determine whether the patient has improved or worsened. However, as an individual patient's performance improves and approaches the maximal possible score, it becomes important to understand whether that patient's score would be within normal limits for a healthy child.

Early in the development of the CMAS it was realized that normal performance of some of the maneuvers might be age or sex dependent. For example, it was anticipated that some healthy 5 year olds might not be able to achieve a perfect score for the head lift, leg lift/duration, or sit-up—either because of normal developmental immaturity or because of age-related difficulty concentrating and cooperating.

Therefore, the study reported here was designed to document how successfully healthy children of different ages and sex are able to perform CMAS maneuvers. Because we anticipated that performances of the sit-ups and the timed maneuvers (head lift, straight leg lift/duration, and arm raise/duration) were most likely to be age and sex dependent, the study focused on these 4 maneuvers. The supine to prone, supine to sit, floor sit, floor rise, and chair rise maneuvers were also studied (Table 1). Other current CMAS maneuvers were not specifically studied because these maneuvers were added to the final version of the CMAS after this study of normal scores for the other 9 maneuvers had commenced.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Healthy children, age 4–9 years, were recruited from an urban elementary school, a suburban elementary school, and 2 suburban child care centers in Columbus, Ohio. Approval from the Columbus Children's Hospital Institutional Review Board was obtained prior to recruitment. A total of 303 healthy children from Columbus participated in the study, with ∼50 children (25 boys and 25 girls) in each age group. The racial distribution of the children was 70% white, 24% African American, and 6% other.

The children were asked to perform the 9 CMAS maneuvers listed in Table 1 on 2 separate occasions, at least 1 week apart. Each time, they performed the maneuvers in the order listed and according to the same instructions routinely provided in the clinical setting.

For analysis of individual maneuvers, statistical methods included descriptive statistics for the maneuvers and log-linear models for inferential tests of the effects of age and sex on measures that demonstrated variability. The log-linear models were tested using the Catmod procedure of SAS version 8.2 (SAS Institute, Cary, NC). Saturated models were fit by maximum likelihood for each maneuver by sex, age, and all interactions. Individual model term effects were tested by chi square. Reduced log-linear models were constructed from factors that were nearly significant in the saturated model (P < 0.1), and the overall model fit was tested by assessing the likelihood ratio. Individual factors were considered significant at P < 0.05, and overall model fit was considered adequate at P > 0.10. Box plots were created using SPSS version 10.0 (SPSS, Chicago, IL). Regression equations were used to test age, sex, and age by sex for maneuvers measured in seconds.

Data from the 9 individual maneuvers were then used to create a composite score, the CMAS-9. This was calculated by adding the scores from each item, giving a total score that ranged from 0 (very poor physical function and strength) to 37 (very good physical function and strength). CMAS-9 scores were calculated for the healthy children described in this study, as well as for a second cohort of children with juvenile IIM (5). In the juvenile IIM cohort, the CMAS-9 highly correlated with the total CMAS score (Spearman's r = 0.99, P < 0.0001) (5). Then, age- and sex-matched norms for the CMAS-9 were developed from CMAS-9 scores in these 2 cohorts, using the following method: First, several definitions of the form “The normal CMAS-9 score for this age and sex is the score that can be achieved by X% of normal healthy children,” were developed, where X was 75, 80, 85, 90, 92.5, and 95. These definitions were then applied to the healthy and juvenile IIM cohorts to generate estimates of sensitivity and specificity for each definition. A receiver-operator characteristic curve was then generated by graphing sensitivity on the x-axis and 1 – specificity on the y-axis. The definition that provided the highest combination of sensitivity (an abnormal test in the juvenile IIM cohort) and specificity (a normal score in the healthy cohort) was determined, and was then used to generate age- and sex-matched normal scores in the healthy population.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

There was no statistically significant difference between the scores healthy children achieved at their first and second testing. This was true for girls and boys of all ages and for each individual maneuver. Accordingly, results from the second testing were used for further analysis.

All healthy children, at all ages, were able to achieve maximum possible scores for the following 5 maneuvers: supine to prone, supine to sit, floor sit, floor rise, and chair rise. In addition, all but 1 4-year-old boy and 1 4-year-old girl achieved a maximum possible score for the arm raise. (Both had scores of 3 instead of the perfect score of 4.)

Results for the head lift, leg lift, and sit-up maneuvers revealed age-related and, to a lesser extent, sex-related variability.

Head lift

Table 2 shows the percentage of children within each age group that received the various possible scores for the head lift maneuver. For example, none of the 4-year-old boys received a score of 0 (the lowest possible score), and none received a perfect score of 5. Eighty-four percent of 4-year-old boys and 60% of 4-year-old girls received a score of 1 or 2. The ability of children to achieve a perfect score steadily increased with age (χ2 = 66.58, P < 0.001).

Table 2. Head lift: percentage of each age group that achieved each score*
 Unable1–9 sec10–29 sec30–59 sec60–119 sec≥120 sec
Age group012345
  • *

    sec = seconds.

4 years, boys038461240
4 years, girls0204020200
5 years, boys016364404
5 years, girls0840202012
6 years, boys0035351911
6 years, girls0023273119
7 years, boys00882856
7 years, girls004242448
8 years, boys00002080
8 years, girls00443656
9 years, boys0007885
9 years, girls000121375

When only the ordinal scores (0–5) were analyzed, there was a statistically significant difference between age groups, but not sex. This was determined by constructing a reduced log-linear model of the head lift score by age and sex factors—which resulted in a good-fitting model (likelihood ratio P = 0.46) that showed age, but not sex, to be significant (χ2 = 111.6, P < 0.0001 for age and χ2 = 0.38, P = 0.54 for sex). No statistically significant difference was found between the ordinal scores (0–5) of girls and boys (χ2 = 3.32, P = 0.068).

When head lift results were expressed in number of seconds (rather than as a score of 0–5), a regression model revealed that age (b = 16.2 seconds, P < 0.001), sex (b = –35.3 male, P < 0.009), and age by sex (b = 5.1, P < 0.01) were significant.

The box plot (Figure 1) shows the median, 25th percentile, and 75th percentile regarding the number of seconds healthy children of different ages were able to maintain a head lift. Girls aged 4, 5, and 6 performed better than age-matched boys, whereas 7-, 8-, and 9-year-old boys performed better than age-matched girls.

thumbnail image

Figure 1. Box plot, indicating the duration (in seconds) that boys and girls of different ages are able to maintain a head lift. The top of the box represents the 75th percentile, the bottom of the box represents the 25th percentile, and the dark horizontal line within the box represents the median number of seconds.

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Leg lift

Table 3 indicates the percentage of children within each age group that received the various possible scores for the straight leg lift/duration maneuver. Note that perfect scores were achieved by all 5-, 6-, 7-, and 9-year-old girls and by all but 1 8-year-old girl; and by all 7-, 8-, and 9-year old boys and all but 1 6-year-old boy. Thirty-two percent of 5-year-old boys and 0% of 5-year-old girls failed to achieve a perfect leg lift score (a statistically significant difference, χ2 = 9.52, P = 0.002). Twenty-seven percent of 4-year-old boys and 8% of 4-year-old girls failed to achieve a perfect leg lift score, but this was not statistically significant (χ2 = 3.14, P = 0.08).

Table 3. Leg lift: Percentage of each age group that achieved each score*
 Unable1–9 sec10–29 sec30–59 sec60–119 sec≥120 sec
Age group012345
  • *

    sec = seconds.

4 years, boys00002773
4 years, girls0004492
5 years, boys004121668
5 years, girls00000100
6 years, boys0004096
6 years, girls00000100
7 years, boys00000100
7 years, girls00000100
8 years, boys00000100
8 years, girls0000496
9 years, boys00000100
9 years, girls00000100

Although sex and the score by sex interactions were significant factors (χ2 = 14.7, P = 0.0001; χ2 = 17.2, P = 0.0006, respectively) in the 2-factor reduced log-linear model, the likelihood ratio (513.11, P < 0.001) suggested that sex was not a particularly good variable to predict success of the maneuver. With this model, there was no significant effect of age for this maneuver. However, if sex is dropped from the model, then age by leg lift is significant, though the model fit is still poor (likelihood ratio = 166.1, P < 0.001).

The leg lift data, when expressed in number of seconds, were not conducive to regression analysis, because a high percentage of all children were able to maintain a leg lift for 120 seconds (at which point the maneuver ceased per the study design).

When the results of the head lift are compared with those of the straight leg lift, it is evident that children in all age groups had more difficulty performing the head lift than the leg lift.

Sit-ups

Results for the sit-up maneuver were the most variable (Table 4). Only 16% of 4-year-old girls and boys were able to perform more than the first 3 sit-ups. A perfect score was not universally achieved by older children: 73% of 9-year-old boys and 71% of 9-year-old girls achieved a perfect score for this maneuver.

Table 4. Sit-ups: percentage of each age group that achieved each score
Age group0123456
4 years, boys4281915808
4 years, girls4001628844
5 years, boys124202028412
5 years, girls441620202412
6 years, boys00811232730
6 years, girls04427312311
7 years, boys0001642060
7 years, girls4048162048
8 years, boys000442468
8 years, girls0081682840
9 years, boys008001973
9 years, girls000138871

Whereas scores varied significantly with age, they did not convincingly vary with sex. In the saturated log-linear model, significant factors were the maneuver (P = 0.019), the maneuver by age (P < 0.0001), and marginally, sex (P = 0.056). In the reduced model of sex (P = 0.55), maneuver (χ2 = 32.37, P < 0.0001), and maneuver by age (χ2 = 80.34, P < 0.0001), sex was no longer significant after controlling for age. The likelihood ratio for the reduced model (19.8, P = 0.84) indicated a good fit for the model.

Normal CMAS-9 scores

The receiver-operator curve that was used to determine which definition of normal offered the best balance of sensitivity and specificity is shown in Figure 2. The 90% definition was thought to offer the best combination of sensitivity and specificity, with a sensitivity of 68% and specificity of 87%. The 90% definition produced the age- and sex-related normal scores for the CMAS-9 shown in Table 5.

thumbnail image

Figure 2. Receiver-operator characteristic curve (graph of sensitivity versus 1 – specificity) for definitions of a normal Childhood Myositis Assessment Scale (CMAS-9) score. Definitions are of the form “The normal CMAS-9 score for children of this age and sex is the score that can be achieved by X% of normal, healthy children,” where X was 95, 92.5, 90, 80, and 75. This curve suggests that the 90% definition offers the best combination of sensitivity (68%) and specificity (87%).

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Table 5. Normal CMAS-9 scores*
AgeGirls score (% of maximum)Boys score (% of maximum)Maximum
  • *

    Ninty percent of healthy children are able to achieve these scores at these ages. CMAS-9 = Childhood Myositis Assessment Scale.

427 (73)26 (70)37
530 (81)25 (68)37
631 (84)31 (84)37
732 (86)32 (86)37
833 (89)35 (95)37
932 (86)35 (95)37

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

This study revealed that normal healthy children, particularly younger children, are not necessarily able to achieve maximum possible scores for some CMAS maneuvers. Normal scores for the head lift maneuver are age and sex dependent. Normal scores for the leg lift maneuver are much less age and sex dependent. Results of the sit-up maneuver are the most variable and vary with age but not with sex. Although all healthy 9-year-old children can be expected to achieve a maximum possible score for the leg lift, some are unable to achieve a maximum possible score for the sit-up and head lift maneuvers.

This age- and sex-dependent variability in performance of certain CMAS maneuvers is reflected in failure of a substantial number of healthy children to achieve a perfect score of 37 on the CMAS-9. Although the CMAS-9 cannot be used to determine normal scores for the published 14-maneuver CMAS instrument (CMAS-14), given that we have no normative data on 5 of the CMAS-14 maneuvers, these results do demonstrate that even for children as old as 9 years, a perfect CMAS-14 score of 52 may not be a reasonable expectation for all children. Awareness of this fact may influence treatment decisions, such as whether to wean medications. More detailed normative data will be required to determine what constitutes a normal age- and sex-matched CMAS-14 score.

Normal scores generated by this study are of considerable value in the interpretation of the CMAS-14 scores of children with juvenile IIM. Even with the availability of these normative data, however, a considerable amount of clinical judgment is usually needed to decide whether a younger child's less than perfect scores for the head lift, straight leg lift/duration, and sit-up maneuvers are within normal limits, or reflective of clinically significant weakness. The clinician must also decide whether any CMAS-14 score he or she judges to be slightly abnormal is so because of ongoing low-grade disease activity, or because of residual damage (without currently active disease), or a combination of both (6).

Furthermore, it is possible that anthropomorphic factors may influence performance of these maneuvers, both by patients and healthy children. For example, it is possible that proportion of leg length (or weight) to trunk length (or weight) could influence performance of the sit-up and leg lift maneuvers. Proportion of body length (especially trunk length) to length of the lever arm may be a significant factor in performance of the head lift. In this study, these anthropomorphic considerations were not sufficiently studied or controlled.

It must be pointed out that use of the CMAS-14 to serially follow children with IIM in the rheumatology clinic is not equivalent to using this instrument to test healthy volunteers. The attitude, motivation, and drive with which children with IIM perform the CMAS maneuvers are not necessarily the same as that seen in healthy children. Children with IIM are usually highly motivated and work very hard to achieve good scores because they sense that their performance on the CMAS is being used to determine their progress and medication needs. As a group, the healthy children in this study did not seem as highly motivated as their age-matched patient counterparts. Some of the younger healthy children in the study may have had lower scores than they were truly capable of achieving, perhaps because they could not equally appreciate the value and reasons for providing maximal effort. It is also possible that a “practice effect” gives patients an advantage.

Although the normal values presented in this article reveal the difficulty in comparing a patient's CMAS performance with that of healthy children of the same age, it should be realized that the primary purpose of the CMAS is to objectively and quantitatively compare a given patient's current performance with his or her past performances. Secondary purposes include comparison of each patient's serial CMAS scores to those of other patients, accounting for age and sex effects, and comparison of an individual patient's CMAS performance with that expected from healthy children of the same age and sex. The data presented here should help clinicians in interpreting the CMAS scores of their patients in the context of normative data derived by age and sex.

Approximately 20% of children with juvenile IIM are <4 years old at the time of disease onset (7). Because our data show that scores for at least some of the CMAS maneuvers are age dependent, it will be important to test 2- and 3-year-old children. Because a significant percentage of healthy 9-year-old children were not able to achieve a perfect score for some maneuvers (most notably, sit-ups), it will also be important to study children older than 9 years of age. Five new CMAS maneuvers were added after our study of healthy children was commenced. Therefore, another study of all 14 CMAS maneuvers in a large group of healthy children, with ages ranging from 2 to 15 years, should be conducted.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

We thank Gloria Higgins, MD, PhD, Holly Cintas, PhD, and Michal Harris-Love, MPT, CSCS for their very helpful comments and suggestions. We also thank Kathy Kirkpatrick, MSW for her invaluable help in organizing and conducting the study.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES
  • 1
    Rider GL, Miller FW. Classification and treatment of the juvenile idiopathic inflammatory myopathies. Rheum Dis Clin North Am 1997; 20: 94353.
  • 2
    Rider GL, Miller FW. Idiopathic inflammatory muscle disease: clinical aspects. Bailliere's Clin Rheumatol 2000; 14: 3754.
  • 3
    Rennebohm RM. Juvenile dermatomyositis. Pediatr Ann 2002; 31: 42633.
  • 4
    Lovell DJ, Lindsley CB, Rennebohm RM, Ballinger SH, Bowyer SL, Giannini EH, et al. Development of validated disease activity and damage indices for the juvenile idiopathic inflammatory myopathies. II. The Childhood Myositis Assessment Scale (CMAS): a quantitative tool for the evaluation of muscle function. Arthritis Rheum 1999; 42: 22139.
  • 5
    Huber AM, Feldman BM, Rennebohm RM, Hicks JE, Lindsley CB, Perez MD, et al. The Childhood Myositis Assessment Scale (CMAS) is a validated measure of physical function and muscle strength in the juvenile idiopathic inflammatory myopathies (JIIM). Arthritis Rheum 2002; 46 Suppl: S2167.
  • 6
    Miller FW, Rider LG, Chung YL, Cooper R, Danko K, Farewell V, et al. Proposed preliminary core set measures for disease outcome assessment in adult and juvenile idiopathic inflammatory myopathies. Rheumatology 2001; 40: 126273.
  • 7
    Pachman LM, Hayford JR, Chung A, Daugherty CA, Pallansch MA, Fink CW, et al. Juvenile dermatomyositis at diagnosis: clinical characteristics of 79 children. J Rheumatol 1998; 25: 1198204.