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Revista chilena de pediatría

versión impresa ISSN 0370-4106

Rev. chil. pediatr. vol.88 no.1 Santiago  2017 

Original Article


Upper limb functional assessment scale for children with Duchenne muscular dystrophy and Spinal muscular atrophy


Raúl G. Escobara,b, Nayadet Lucerob, Carmen Solaresc,d, Victoria Espinozac,d, Odalie Moscosob, Polín Olguínc,d, Karin T. Muñozb,e, Ricardo Rosasc,d,*

aNeurology Unit, Pediatrics Division, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
bPediatric Neurorehabilitation and Neuromuscular Laboratory, Clinical Hospital, Red de Salud UC-CHRISTUS, Santiago, Chile
cSchool of Psychology, Pontificia Universidad Católica de Chile, Santiago, Chile
dInclusion Technology Development Center, Pontificia Universidad Católica de Chile (CEDETi UC), Santiago, Chile.
eKinesiology Career, UDA of Health Sciences, Faculty of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile

Correspondencia a:

Introduction: Duchenne muscular dystrophy (DMD) and Spinal muscular atrophy (SMA) causes significant disability and progressive functional impairment. Readily available instruments that assess functionality, especially in advanced stages of the disease, are required to monitor the progress of the disease and the impact of therapeutic interventions. Objective: To describe the development of a scale to evaluate upper limb function (UL) in patients with DMD and SMA, and describe its validation process, which includes self-training for evaluators. Patients and Method: The development of the scale included a review of published scales, an exploratory application of a pilot scale in healthy children and those with DMD, self-training of evaluators in applying the scale using a handbook and video tutorial, and assessment of a group of children with DMD and SMA using the final scale. Reliability was assessed using Cronbach and Kendall concordance and with intra and inter-rater test-retest, and validity with concordance and factorial analysis. Results: A high level of reliability was observed, with high internal consistency (Cronbach  = 0.97), and inter-rater (Kendall W = 0.96) and intra-rater concordance (r = 0.97 to 0.99). The validity was demonstrated by the absence of significant differences between results by different evaluators with an expert evaluator (F = 0.023, p > .5), and by the factor analysis that showed that four factors account for 85.44% of total variance. Conclusions: This scale is a reliable and valid tool for assessing UL functionality in children with DMD and SMA. It is also easily implementable due to the possibility of self-training and the use of simple and inexpensive materials.

Keywords: Neuromuscular diseases; Scale; Function; Duchenne muscular dystrophy; Spinal muscular atrophy; Upper limb.



Neuromuscular diseases (NMD) are those that affect the peripheral nervous system resulting in muscular strenght loss. In pediatric age, most NMDs lack curative treatment and involve a significant functional compromise, leading to progressive disability. Any neurological rehabilitation program that helps these patients requires instruments to monitor functionality, prevent secondary disorders, provide a common language among professionals involved, and especially to evaluate the effect of different therapies.

Among pediatric NMDs, Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA) are the most common, with DMD as the most prevalent and both progressive and highly disabling1,2. Diverse function assessment tools have been described for DMD and SMA3–5. Among these instruments are those that evaluate motor function aspects of daily life activities and which, have a greater clinical benefit by including life-limiting concepts, highlighting the most relevant functional aspects of the patient.

Among the instruments described are those based on self-report 6–8, which provide information that allows the individual’s ability to interact with society and his/her level of independence to be measured, but they have important limitations as they are not able to control non-matching variables. On the other hand, there are instruments that are based on the observation of an experienced evaluator, using standard procedures and following precise instructions and defined materials. These characteristics make them more objective and useful in evaluating more accurately the evolution of the disease, in addition to deliver adequate final criteria that is crucial when evaluating the effectiveness of therapeutic interventions. However, some authors argue that the application of these instruments at different centers and without adequate training of evaluators can affect their reliability 9,10. The above challenges the use of these instruments, which becomes even more difficult when considering the need for translations when the instruments are originally in other languages10.

In recent years, the emergence of new therapies for DMD and SMA has led to a series of clinical trials that required functional evaluation tools to assess their effectiveness 1–13. This has helped us to know the validity and reliability of these instruments, which, however, have been focused on early stages of the disease prior to the inability of walking 10,14–16. There are only a few evaluation tools to monitor the functionality in non-ambulant patients. Strength monitoring, through manual dynamometry, can give an objective account of the progression of strength loss after walking loss or before this occurs17,18. However, these assessments provide limited information on overall patient functionality and have important application limitations in more advanced stages of the disease. Upper limb function evaluation (UL) has been proposed as an adequate alternative for this purpose, therefore, instruments that aim to evaluate the effect of the loss of strength on UL have been developed 6,19–24.

The development of instruments to evaluate the evolution of NMDs, such as DMD and SMA, which provide objective information to assess the impact of therapeutic interventions, especially in patients who have already lost ambulation, is crucial for a proper management of these patients. These instruments are of key importance and should be accessible to professionals in charge of patients with NMDs, without resulting in excessive medical expenses. These instruments should be designed with inexpensive and easily acquired materials, have manuals and instructions that promote self-learning and be available in the language of the evaluator and the population to be evaluated.

The objectives of this study are to report the development of a scale specifically made to evaluate UL function, its application in patients with DMD and SMA, and describe its validation process, which includes self-training for evaluators.

Patients and Method

Design and development of the scale

Initially, other scales specifically designed or adapted to evaluate NMDs functionality were reviewed5,6,21–23,25–28. Afterwards, a group of experts (pediatric neurologist specialized in NMDs, pediatric neurologist specialist in neurorehabilitation, occupational therapist, kinesiologist), with extensive experience in the management of pediatric patients with NMDs, reviewed the items intended to evaluate UL functionality, choosing an initial list of 17 items. Then, 4 additional items were added, aiming to reflect limitations in activities of daily living (ADL) in non ambulant patients with NMDs. The list included a total of 21 items, which were applied to 8 healthy children (between 5 and 12 years of age) and then to 4 children with NMD (between 10 and 16 years of age). Eight items were modified according to the evaluations made creating the final list.

The final version of the scale included 21 items, which were grouped into 4 dimensions, similar to the one proposed by Mayhew29. Each item has a score from 0 to 5, except 5 of them that score between 0 and 4. The scale has a total score that ranges between 0 and 120.

Subsequently, a detailed manual about the application of the scale and the implementation of the necessary kit was written. In order to have a model, the scale application to a healthy adult was filmed. This video was watched by 4 therapists, and based on their comments, modifications to the manual were made to obtain consistency between the images and the instructions.

The occupational therapist (OT), who participated in the scale design, evaluated a total of 10 patients with NMD (between 10 and 19 years of age), in 2 sessions, each separated by 2 weeks. These sessions were filmed so that the implementation of the scale could be scored by other evaluators. Prior to the scale implementation, the OT applied Barthel’s index (BI) to each of the patients in the first session 30. BI index is a 10-item scale that measures functional independence in the domains of personal care and mobility. The total score ranges between 0, total dependence, to 100, total independence. The validity and reliability of BI has been clearly established31,32.

Evaluator training

After completing the above, 5 experienced therapists working with children with neurological disabilities (2 OT and 3 kinesiologists), became self-trained in the application of the scale using the manual and video (both available at: The frequency and time for review of the material was determined by each therapist; also, they were able to ask clarifying questions to the OT that participated in the design of the scale.

Evaluator reliability

After the self-training phase, the evaluators received the assessment of each of the children performed by the OT, in addition to a set of the scale application guidelines. Evaluators performed the assessments consecutively, finalizing one process before starting the next. Each of the 5 evaluators applied the scale to the 10 patients, for a total of 50 evaluations (5 evaluations for each patient). After 8 weeks of the first round, evaluators repeated the assessments in the same way, completing 2 evaluations (test, re-test) for each of the 10 patients.


The sample was non-randomized and formed by 10 subjects, 8 DMD and 2 SMA, who had been followed up for at least 4 years in the Pediatric Neurorehabilitation and Neuromuscular Diseases Unit, all with confirmed diagnosis by genetic-molecular study. The mean age of subjects was 12.8 years (range: 9.4 to 19.1). One of the patients with SMA was female. Three of the 10 patients were non-ambulant, all of them were DMD ans under corticoidal treatment. The other 5 patients with DMD had suspended corticosteroids since the inability of walking, at least a year earlier.

All participants completed their baseline assessments safely and without difficulty. The average time of the evaluation was 20 min (range: 15 to 23) and there was no evidence of fatigue in any of the subjects.

The study was approved by the ethics committee of the School of Medicine of the Pontifical Catholic University of Chile.

Statistical Analysis

Validity and reliability of the scale were evaluated with various analyzes detailed in the Results section. For all statistical tests, p values ​​of less than 0.05 were considered significant. Statistical package SPSS® version 22 was used for analyzes.


Reliability of scale

The first source of reliability is a measure of internal consistency analyzed by Cronbach’s alpha. The result obtained is α = 0.97, showing a very high internal consistency.

The second is a measure of objectivity that helps us to determine how consistently judges evaluate the same cases using the scale. To do this, 5 judges were presented a total of 3 videos with fictitious cases. The evaluations were submitted to a Kendall coefficient of concordance W, obtaining a result of W = 0.96, a high and very significant concordance among judges (p <0.01).

The third is a test-retest measure among judges. Six judges evaluated 10 videos of real cases two months apart. The average Pearson correlation between the first and second evaluation was between 0.97 and 0.99 (table 1), indicating a high consistency among judges’ assessments.

Table 1. Pearson intra-rater correlation index

Validity of the scale

The first evidence, related to validity of the scale content, is assured by the process of development of its items by experts, which was previously described in the section of Patients and method. In addition, content analysis was performed by a group of experts outside the team in charge of development.

The second source of validity, considered as evidence of concurrent validity, is the concordance of the scale results among judges, with the evaluation carried out by the evaluator 1, who is the expert judge, regarded as the measurement pattern. When comparing the means of the 5 judges with this expert, a non-significant difference was obtained (F = 0.023, p > 0.5).

A third source of evidence, which supports concurrent validity, is obtained by comparing the results of the scale with BI, which showed an average score of 48 among the 10 patients (range 20 to 90). Although BI contains aspects not evaluated by our scale, the correlation was very high and significant (r = 0.93).

Finally, we have evidence of scale development validity through factor analysis (table 2). A Factorial analysis of the scale indicated 4 factors that explain 85.44% of the total variance. The first factor is proximal functionality, the second middle functionality, the third distal functionality and the fourth is of mixed functionality. The first one includes items of shoulder functionality and the process of putting on a T-shirt. The second one involves the processes of bringing hands to the mouth, transfer weight from the thighs to the table or to shoulder height with the two hands, lift and transfer cans, move weight from one circle to another, draw path on a paper, bring a full can to mouth, bring a spoon to the mouth, combing and brushing their teeth. The third one is the process of tearing a piece of paper and lifting an object with 2 point grip and opening the lid of a container. The fourth one consists of grabbing 5 coins and opening a bottle.

Table 2. Factorial analysis of the scale

It is interesting to note that the most complex items on the scale, those that have significant factor weights in more than one factor, are precisely those that evaluate functionality of daily activities, such as putting on a T-shirt, bringing a full can to the mouth, bringing a spoon to the mouth, combing and brushing the teeth.

Discussion and Conclusions

This article describes an UL function scale evaluation in children with lack of strength secondary to 2 of the most frequent NMDs in pediatric age, DMD and SMA. The application of the scale requires a process of self-training and the use of inexpensive and easily acquired materials to create the stimuli used during the application. This scale proves to be highly reliable and shows a high concordance among and within the evaluators.

The need to have an UL function evaluation instrument in patients with progressive loss of muscle strength, especially in stages near or after the inability of walking, is due to the fact that these children present significant axial and lower extremity lack of muscle strength. This results in that the activities that these patients can perform the best are those that involve the use of their upper limbs, usually not considered in most of the existing scales of functionality16–18.

In the selection, aspects that were not the exclusive expression of muscular strength, but reflected the ability to perform functional actions were included. We selected those tests already reported in the literature and which seemed to us more representative of strength-associated functionality5,6,21–23,25–28. The scale developed showed excellent reliability, with a very high internal consistency (Cronbach’s of 0.97).

The fact that the loss of muscular strenght in muscular and second motor neuron disorders is characterized by a proximal to distal progression should be considered when grouping the items of an evaluation scale for this type of disease, if differentiate degrees of strength expressed in functionality is intended. Mayhew et al. suggested grouping the items in 3 levels: high, middle and distal29. However, it is important to consider that the functionality of specific actions is affected by compensatory strategies that each patient develops through the evolution of the disease, and it is not only altered by the lack of strength in certain body parts such as the shoulders, elbows and/or wrists. Therefore, we thought that it was important to consider functionality actions represented by basic ADLs involving different segments of the upper limbs. Our scale was built in 4 dimensions: proximal, middle, distal and mixed functionality.

The factorial analysis of the scale was valid not only when it showed that 4 factors explain 85% of total variance, but also when described the presence of items with significant factorial weights in more than one factor. All these complex items correspond to the mixed functionality dimension. On the other hand, the high scale correlation (r = 0.97) with another instrument widely used in the evaluation of ADLs in DMD, such as BI33,34, provides further evidence of its validity. In addition, BI has shown an important floor effect when applied to very weak patients with DMD and poor motility, suggesting the need to use instruments capable of adequately evaluating functionality in patients with a high degree of functional compromise 35, something that our scale shows to be capable of doing.

Literature suggests that the use of functional assessment instruments, based on clinical observation, requires specific training of the evaluator to achieve adequate reliability and consistency 9,10,28,36,37. This aspect limits their use as training is not always readily available to the evaluators. Our scale, applied by self-trained evaluators, showed a high inter-evaluator agreement with a Kendall W coefficient of 0.96 (p <0.001) and an average intra-judges correlation greater than 0.97, proving the effectiveness of the self-learning strategy. The high levels of reliability obtained in the application of the scale make possible to avoid the need for training for a correct application. Another advantage that presents the scale is the easy implementation of the battery used, formed by elements constructed with accessible and low cost materials. Finally, the scale is in Spanish, overcoming another limitation described in the literature regarding the lack of instruments developed in this language and the need of translation of instruments that have been validated in other languages10.

The limited number of participants may be considered a weakness of the study, especially in the case of SMA. However, this does not detract from the findings, since there was no difference in the results obtained between those patients who maintained the ability to walk with respect to those who had lost it. There was also no difference between children with DMD compared to children with SMA. Therefore, this scale is able to provide objective information on UL functionality in these patients, even at different stages of the evolution of the disease. Future studies involving a greater number of patients, both with DMD and SMA at different stages of the disease, and other types of myopathies with significant strength compromise, especially UL, are crucial.

In summary, this scale is a reliable and valid instrument to evaluate UL functionality in children with DMD and SMA between 9 and 19 years of age. In addition, it is easy to implement due to the possibility of self-training and the use of simple and inexpensive materials.



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Ethical Responsabilities

Protection of people and animals: The authors reported that no experiments on either people or animals have been performed.

Confidentiality of personal data: The authors reported that they have followed the protocols of their center regarding the publication of personal data.

Privacy rights and informed consent: The authors have obtained the informed consent from patients and/or subjects referred to in the article. These documents are in the possession of the corresponding author.


Project funded by Vice-Rectory for Research, UC Interdisciplinary Research Center, Pontifical Catholic University of Chile.

Conflict of interests

The authors declare no conflict of interest.


We thank the therapists Rodolfo Aviles, Vanesa Bron, Miguel Jorquera, Loreto Quezada, Maria Paz Salinas y Bernardita Severin; all part of the staff at Pediatric Neurorehabilitation and Neuromuscular Diseases Unit, Catholic University of Chile, for your help to determine the validity and reliability of the scale.

Received 5-1-2016; Accepted: 7-13-2016.

Correspondencia a:

Raúl G. Escobar

Ricardo Rosas

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