Distribution and severity of weakness among patients with
polymyositis, dermatomyositis and juvenile dermatomyositis
M. O. Harris-Love1,2,3, J. A. Shrader3, D. Koziol4, N. Pahlajani5, M. Jain3, M. Smith3, H. L. Cintas3,
C. L. McGarvey3, L. James-Newton2, A. Pokrovnichka5, B. Moini5, I. Cabalar5, D. J. Lovell6,
R. Wesley4, P. H. Plotz5, F. W. Miller2, J. E. Hicks3and L. G. Rider2
Objective. To describe the distribution and severity of muscle weakness using manual muscle testing (MMT) in 172 patients with PM, DM
and juvenile DM (JDM). The secondary objectives included characterizing individual muscle group weakness and determining associations
of weakness with functional status and myositis characteristics in this large cohort of patients with myositis.
Methods. Strength was assessed for 13 muscle groups using the 10-point MMT and expressed as a total score, subscores based on
functional and anatomical regions, and grades for individual muscle groups. Patient characteristics and secondary outcomes, such as clinical
course, muscle enzymes, corticosteroid dosage and functional status were evaluated for association with strength using univariate and
Results. A gradient of proximal weakness was seen, with PM weakest, DM intermediate and JDM strongest among the three myositis clinical
groups (P?0.05). Hip flexors, hip extensors, hip abductors, neck flexors and shoulder abductors were the muscle groups with the greatest
weakness among all three clinical groups. Muscle groups were affected symmetrically.
Conclusions. Axial and proximal muscle impairment was reflected in the five weakest muscles shared by our cohort of myositis patients.
However, differences in the pattern of weakness were observed among all three clinical groups. Our findings suggest a greater severity of
proximal weakness in PM in comparison with DM.
KEY WORDS: Myositis, Manual muscle test, Strength, Rehabilitation.
The idiopathic inflammatory myopathies (IIMs) result in chronic
skeletal muscle inflammation and weakness . PM, DM, juvenile
DM (JDM) and IBM are the major subtypes of IIM, differ-
entiated by clinical, histopathological and immunological features
[1, 2]. Therapy consists of anti-inflammatory and immunosup-
pressive agents .
The impaired force-generating capacity of skeletal muscle
secondary to chronic muscle inflammation and residual muscle
atrophy and scarring in IIM contribute to functional limitation,
disability and decreased health-related quality of life [3, 4]. Peak
muscle force is most relevant in the assessment of IIM disease
activity and treatment responses , most commonly measured
by the manual muscle test (MMT). The International Myositis
Assessment and Clinical Studies Group (IMACS) and Pediatric
Clinical Trials Organization (PRINTO) identified muscle strength
assessment as a top core set measure, along with physician global
disease activity in myositis patients [5, 6].
Most myositis therapeutic trials conducted over the past two
decades incorporated the MMT as a primary outcome measure
[5, 7], but differed widely in its use. Trials featured summed
MMT scores derived from 4 to 20 muscle groups  and have
incorporated different MMT grading scales, including the Medical
Research Council 5-point scale and an expanded 10-point scale
. In addition, previous IIM natural history and clinical outcome
studies have not characterized weakness of individual muscle
The primary aim of this investigation is to describe the
distribution and severity of muscle weakness measured with
MMT in 172 patients with PM, DM and JDM enrolled in natural
history studies. Secondary aims include characterizing individual
muscle group weakness and determining associations of muscle
weakness with other myositis illness characteristics in this large
cohort of patients with myositis.
Patients and methods
We utilized a cross-sectional, retrospective design with a 172
patient sample of probable or definite PM, DM or JDM
confirmed by Bohan and Peter criteria of IIM patients seen
at the National Institutes of Health (NIH) Clinical Center from
1994 to 2005 . Included subjects were ?5yrs of age, and
examined by an adult or paediatric rheumatologist and a physical
therapist, receiving a standardized MMT evaluation. Sixty-five
had PM, 50DM and 57 JDM. Six with PM, 6 with DM and 3 with
JDM were diagnosed with myositis and another autoimmune
disease (systemic lupus, scleroderma, SS or JRA). Of those with
JDM, four patients were 4.6–6 yrs of age and five participants
were between 7 and 8 yrs of age; five were >18 yrs of age, with
a maximum age of 34.9 yrs. Patients and parents of juvenile
patients provided written informed consent and were enrolled in
NIH institutional review board approved studies of myositis
natural history. Only patients with a complete MMT by a physical
therapist were eligible.
Manual muscle testing
Physical therapists experienced in examining IIM patients
administered the MMT using standardized instructions, position-
ing and stabilization techniques established by Kendall et al. .
1George Washington University, School of Medicine and Health Sciences,
Research, National Institute of Environmental Health Sciences,
Medicine Department (RMD),
Diseases, National Institutes of Health (NIH), Department of Health and Human
Services, Bethesda, MD and
Hospital Medical Center, Cincinnati, OH, USA.
2Environmental Group,Officeof Clinical
4Biostatistics and Clinical Epidemiology Service,
5National Institute of Arthritis and Musculoskeletal and Skin
6Division of Rheumatology, Cincinnati Children’s
Submitted 30 April 2008; revised version accepted 22 October 2008.
Correspondence to: L. G. Rider, Environmental Autoimmunity Group, NIEHS,
NIH; CRC 4-2352, MSC 1301, 10 Center Drive, Bethesda, MD 20892-1301, USA.
Advance Access publication 11 December 2008
? Published by Oxford University Press on behalf of the British Society for Rheumatology 2008.
Examiners attended a MMT workshop by Florence Kendall,
or viewed seminar videotapes and received instruction from
a Kendall-trained physical therapist, prior to assessing patients in
the study. The total MMT score consisted of 13 muscle groups
(2 unilateral and 11 bilateral), with a maximum (max) value of
240. The 13 muscle groups included in the MMT examination
represent the common muscles tested among all clinical groups
included in our cohort (see Supplementary Table 1, available
as supplementary data at Rheumatology Online). Our inclusion
of these 13 muscle groups reflects the variation of end-point
measures in previous studies , and attempts to comprehensively
describe the clinical presentation of the participants.
The MMT score was organized into regional anatomic groups:
axial, proximal and distal. In addition, the MMT score was
organized into functional anatomic groups: upper extremity and
lower extremity (see Supplementary Table 1, available as
supplementary data at Rheumatology Online). The Kendall
10-point MMT was selected because inter-rater reliability was
established in myositis  and this MMT grading scale, as well as
variations, has been used as a primary outcome measure in IIM
therapeutic trials [29–32]. Pediatric physical therapists adminis-
tered the MMT examination to all children with JDM. These
therapists were instructed to contact the primary investigator or
make a notation in the medical record if subject cooperation or
behavioural factors confounded the MMT results.
We classified the degree of weakness for individual muscles into
four distinct strata: severe, moderate, mild and none. For each
muscle group, MMT was graded 0–3 (severe weakness), 4–6
(moderate weakness), 7–9 (mild weakness) and 10 (no detectable
weakness). We implemented this system based on movement
limitations derived from MMT grading criteria to stratify muscle
weakness based on the patient’s ability to move a body segment
against gravity and withstand examiner-applied manual resis-
tance. Grades 7–9 indicate the ability to move against gravity into
the testing position and hold against varying degrees of applied
manual resistance. Furthermore, Grades 7–9 should be discern-
able from Grade 10, which indicates no detectable strength
impairment. Grades 4–6 indicate considerable difficulty in placing
a limb in the testing position against gravity and sustaining the
testing position against gravity or minimal manual resistance.
Grades 0–3 primarily reflect the inability to move the limb beyond
partial range of motion (<50% of passive range of motion)
against gravity and the need for gravity-minimized testing
Demographic and clinical data included age, BMI, serum levels
of creatine kinase (CK; upper limit of normal value, 252U/l)
and lactate dehydrogenase (LDH; upper limit of normal value,
226U/l), corticosteroid dosage (mg/kg of body weight) and
physician global assessment of disease activity (MD Global
Activity) using a 10-cm visual analogue scale . MD Global
Activity was completed for 35 of 65 patients with PM, 18 of
50 patients with DM and 55 of 57 patients with JDM. Age at
onset was based on the first occurrence of IIM symptoms. Delay
to diagnosis (months) was calculated from the onset date to the
date of IIM diagnosis. Disease duration (months) was calculated
from diagnosis date to examination date at our facility.
Functional status was assessed with the modified Convery
activities of daily living (ADL) scale  derived from the
Convery assessment , administered to 30 of 65 patients with
PM and 15 of 50 patients with DM by a single physiatrist.
The Childhood Myositis Assessment Scale (CMAS) was used to
observe muscle function and endurance in 53 of 57 JDM patients
. Forty-two parents of 57 patients with JDM who were <18 yrs
of age completed the Childhood Health Assessment Questionnaire
(CHAQ) to assess physical dysfunction .
Data were analysed using JMP version 6.0 statistical analysis
software (SAS Institute, Cary, NC, USA), StatXact version 4.0.1
(Cytel Software Corporation, Cambridge, MA, USA) and Stata
Statistical Software, Release 10 (StataCorp, College Station, TX,
USA). Analysis of variance with Tukey–Kramer post hoc tests
was used to determine differences among the groups regarding
interval data for patient characteristics, clinical course and
summed MMT scores. Chi-square or exact tests were used for
Because MMT scores were ordinal, they were summarized
by median and interquartile range for each individual muscle.
MMT total score and MMT subscores based on functional and
anatomical regions, calculated from bilateral summed data, were
summarized as means and standard deviations. Parametric
statistics were used for these summed MMT scores since they
approximated interval data . Summed MMT data were also
expressed as a percentage of the maximum possible score to allow
for comparisons among MMT regional subscores. Because paired
analyses did not reveal differences between right and left
individual MMT grades across all groups, right-sided data were
arbitrarily selected for the analysis and depiction of the MMT
grades for individual muscle groups. The Kruskal–Wallis test was
used to determine differences in individual MMT grades among
the three clinical groups; if significant, the Wilcoxon rank sum test
was used for post hoc pairwise comparisons, using Holm’s
adjustment. To compare subscores of different muscle groups
(e.g. proximal vs distal and upper vs lower), for each patient
a difference between the two subscore groups was calculated using
percentages of maximum scores, and tested for equality to zero
using the one-sample t-test. For comparing ordered categorical
data among the three clinical groups, the Kruskal–Wallis non-
parametric test for singly ordered contingency tables was used.
Univariate and multivariate linear regression models were
used to determine variables associated with muscle strength. An
a priori decision was made to use the proximal MMT score as the
dependent variable based on the prominent degree of proximal
weakness. The coefficient of determination (R2) was used to
estimate the strength of the regression model. The predictor
variables for the regression models were: age, BMI, CK and LDH
serum levels, corticosteroid dosage, disease duration, physician
global assessment of disease activity, and CMAS and CHAQ for
the JDM group and modified Convery ADL scale for PM and
DM groups. For all analyses, a two-tailed P-value of <0.05 was
Patient characteristics and clinical course
A comparison of patient demographics and clinical characteristics
by clinical subgroup is presented in Table 1. No significant
differences between patients with PM or DM were detected for
age, gender, ethnicity, age of onset, delay in diagnosis, cortico-
steroid dosage and serum CK and LDH levels. Disease duration
was significantly greater for PM compared with DM patient
groups (P?0.05). The female to male ratio exceeded 3:1 for both
PM and DM groups. JDM patients had younger age at onset,
lower BMI, higher corticosteroid dosages (mg/kg) and lower
CK levels than the PM or DM groups (P?0.05).
Weakness among the IIM clinical groups
The total MMT score was 180.3?27.3 (75% potential max total
score of 240) in PM, 191.8?22.6 (80% of the potential max total
score) in DM and 202.0?29.9 (84% of the potential max
total score) in JDM (Table 2). Patients with PM were weaker
than JDM based on the total MMT score (P<0.05). Using
subgroups of muscles based on anatomical and functional regions
Weakness in myositis 135
(see Supplementary Table 1, available as supplementary data
at Rheumatology Online), patients with PM were significantly
weaker than the DM and JDM patient groups when comparing
the lower extremity and proximal MMT scores (P?0.05;
Table 2). Upper extremity and distal MMT subscores (85–87%
and 89% of max potential score, respectively) were relatively
higher than the axial MMT subscores for all clinical groups (77%
of max potential score). Paired analyses revealed that proximal
region muscle groups were weaker than the distal region, and
lower extremity groups were weaker than upper extremity groups
within each IIM clinical group (P?0.001; Table 2).
Individual muscle group weakness
We conducted pairwise comparisons of the right and left MMT
grades of each bilateral muscle group. No significant asymmetry
of weakness was detected in the PM, DM or JDM clinical groups
(P¼0.12–1.0). The PM group displayed more weakness in four
muscle groups in comparison with DM. These muscle groups were
the hip flexors, hip abductors, knee extensors and ankle plantar
flexors (hip abductors, P?0.01; all other groups, P?0.05;
In DM, the wrist flexors were significantly weaker than in both
PM and JDM (P?0.05). Over twice the number of patients with
DM had a MMT grade of ?6 for wrist flexors compared with
patients with PM and JDM (Table 4).
Patients with JDM had the least overall weakness among
the three clinical groups. At least 88% of the patients with JDM
had MMT grades for neck extensors, shoulder elevators, elbow
flexors, wrist flexors, wrist extensors, knee extensors, ankle
dorsiflexors and plantar flexors that were in the ‘mild’ or ‘none’
strata for weakness (Table 4). Four muscle groups displayed
appreciable weakness in our JDM cohort (median grade < 9 out
of 10): neck flexors, shoulder abductors, hip flexors and hip
extensors (Table 3). In each of these muscle groups, at least 20%
of the patients had MMT grades in the ‘moderate’ to ‘severe’
strata of weakness (Table 4).
The five weakest muscle groups for all three IIM clinical groups
were the hip flexors, hip extensors, hip abductors, neck flexors and
shoulder abductors (Tables 3 and 4). The severity of weakness
among these muscle groups varied within each clinical group.
Neck flexors, the weakest muscle group in JDM, demonstrated
moderate to severe weakness (MMT grade ?6 out of 10) in 49%
of the patients (Table 4). Neck flexors were only the third and
fourth weakest muscle group for DM and PM. Muscle groups
TABLE 1. Comparison of subject characteristics by clinical group
Gender, female, %
African American, %
Age of onset, yrs
Disease duration, months
Delay in diagnosis, months
Corticosteroid dosage, mg/kg/day
Non-percentage values are expressed as means ? S.D.
PM or DM at the ?0.05 level by Tukey–Kramer Honestly Significant Difference.
significantly different from PM at the ?0.05 level by Tukey–Kramer Honestly Significant
Honestly Significant Difference. (Percentage values in columns may not equal 100% due
aJDM significantly different from
cPM significantly different from DM at the ?0.05 level by Tukey–Kramer
TABLE 2. Comparison of MMT subscores and total MMT score by clinical group
MMT subscorePM (n¼65) DM (n¼50)JDM (n¼57) Maximum possible MMT score
Proximala, n (%)
Distala, n (%)
Axial, n (%)
Upper extremityc, n (%)
Lower extremityc, n (%)
Total MMT, n (%)
Values are expressed as means ? S.D. (percentage of maximum possible MMT score ? S.D.).aDifference between distal subscore and proximal subscore is significantly different within each clinical
group, P?0.001, using one-sample t-test.bEach clinical group is significantly different from the other two groups at the P?0.05 level by Tukey–Kramer Honestly Significant Difference.cDifference
between upper and lower extremity subscore is significantly different within each clinical group, P?0.001, using one-sample t-test.dPM is significantly different from JDM at the P?0.05 level by
Tukey–Kramer Honestly Significant Difference. All comparisons are based on the percentage of the maximum achievable subscore.
TABLE 3. Comparison of individual MMT grades by clinical group
PM (n¼65) DM (n¼50)JDM (n¼57)
Muscle groupsMedian [25%, 75%] Median[25%, 75%]Median[25%, 75%]
Ankle plantar flexorsa
The strength of muscle groups using MMT was compared among clinical groups using the Kruskal–Wallis test; if significant, post hoc pairwise comparisons were done with Wilcoxon rank sum test
and resulting P-values were adjusted by Holm’s method.aPM is significantly different from DM, P?0.05.bDM is significantly different from JDM, P-value ?0.05.cPM is significantly different from JDM,
P-value ?0.01.dDM is significantly different from JDM. P-value ?0.01.eDM is significantly different from PM. P?0.01.
136 M. O. Harris-Love et al.
associated with the hips (flexors, extensors and abductors) were
the weakest muscle groups for both the PM and DM groups.
MMT grades of <10 were observed for the three hip muscle
groups by 86–98% of patients with PM or DM (Table 4).
Associations of myositis characteristics with MMT scores
We examined the association of measures of functional perfor-
mance, myositis disease activity and demographic factors with the
proximal MMT score. Mean modified Convery ADL scale scores
were 51?19.5 out of 91 for 30 of 65 patients with PM and
57?14.3 for 15 of 50 patients with DM, indicating moderate
dysfunction in PM and mild dysfunction in DM. Performance on
the modified Convery ADL scale explained 59% (P<0.0001) and
48% (P<0.005) of the variance of the proximal MMT subscore in
PM or DM in univariate linear regression analyses. Scores of
40?11.0 out of possible 52 for the CMAS (in 53 of 57 patients)
and 0.86?0.91 out of 3.0 for the CHAQ (in 42 of 57 patients)
indicated mild to moderate physical dysfunction in JDM .
Univariate linear regression analysis confirmed that the CMAS
and CHAQ explained 62% (P<0.0001) and 55% (P<0.0001),
respectively of the variance in the proximal MMT subscore in
None of the patient characteristics or myositis activity
measures, such as age, disease duration, prednisone dose, CK
and LDH serum levels, and BMI had a strong association with
proximal MMT subscore. Other than functional performance
measures, the best association with MMT was MD Global
Activity (R2¼0.20–0.21, P<0.01) in the PM and JDM groups.
Patient age (PM) and LDH serum levels (PM and JDM) were
significant, but had a low strength of association with proximal
MMT subscores (R2¼0.07–0.12, P?0.03). Multivariate linear
regression did not significantly improve upon the univariate
models in determining associations with strength.
This cross-sectional study focused on force-generating capabilities
of muscle in IIM measured with MMT. Our findings provided a
data-driven description of weakness patterns in IIM and provided
additional insights into associated muscle dysfunction.
The eleven bilateral muscle groups included in this study were
found to be symmetric in degree of weakness for IIM clinical
groups. We elected to organize the MMT subscores into regional
and functional anatomic muscle groups to better understand the
patterns of muscle weakness in IIM. While the traditional
organization of MMT subscores into regional anatomic groups
is used in the clinical diagnosis of IIM, these subgroups do not
always reflect a functional organization of muscle groups within
the context of basic and instrumental activities of daily living.
We suggest that this functional organization of MMT scores may
provide a construct for improving our understanding of strength
function relationships in future studies (e.g. lower extremity
strength influence on walking speed or chair rise ability). The
severity of lower extremity and proximal muscle group weakness
exceeded that of the upper extremity, axial and distal muscle
groups, consistent with clinical insights of other investigators
[1, 39]. However, our findings suggest that only the proximal
and lower extremity MMT subscores were significantly different
across all patient groups. Identifying and monitoring lower
extremity weakness in patients with IIM is of clinical importance
since impairments of these functional muscle groups have been
associated with increased risk of falls and nursing home placement
for older adults .
While the proximal pattern of weakness in IIM is well known,
less attention has been given to variations in the patterns of
weakness among different IIM clinical groups. Although distal
MMT subscores were higher for all patients, it may be a
distinguishing feature for some IIM clinical groups. Our findings
revealed significantly lower MMT grades for the wrist flexors
in patients with DM and the ankle plantar flexors in patients
Individual muscle groups were stratified based on the 10-point
MMT grading criteria (Table 4). This allowed us to make
distinctions among clinical groups and provide a clinical context
for the MMT results. The proportion of individual MMT grades
in the ‘moderate’ and ‘severe’ range revealed that PM, DM and
JDM share the five weakest muscle groups from both the axial
and proximal regions: neck flexors, shoulder abductors, hip
flexors, hip extensors and hip abductors. These findings provide
data to further refine MMT use as a core set measure  and
clinical guidance regarding the targets of exercise interventions.
Improving our understanding of the distribution and severity of
weakness in IIM is important, and raises a critical question: how
does one interpret MMT scores in the context of functional
performance? Strength demands of walking or rising from a chair
require lower extremity muscle groups to be capable of not only
moving the limbs against gravity, but also supporting and moving
the body weight. Eriksrud and Bohannon  reported that
elderly subjects unable to complete the sit-to-stand task attained
64% of the maximum summed MMT grades for the knee
TABLE 4. Strata of weaknessaby clinical group
PM (n¼65) (percentage of subjects) DM (n¼50) (percentage of subjects) JDM (n¼57) (percentage of subjects)
Muscle groups None MildModerate SevereNone MildModerate SevereNone MildModerateSevere
Ankle plantar flexorsb
aStrata of weakness are based on the MMT grading criteria: no detectable weakness ¼ 10 out of 10, ability to move against gravity into the testing position and hold against maximal manual
resistance; mild weakness ¼ 7–9 out of 10, ability to move against gravity into the testing position and hold against varying degrees of submaximal manual resistance; moderate weakness ¼ 4–6 out of
10, inability to sustain the testing position against gravity (4), inability to withstand minimal manual resistance in the testing position (5) or ability to withstand minimal manual resistance (6); severe
weakness ¼ 0–3 out of 10, inability to move limb beyond partial range of motion (<50% of partial range of motion) against gravity.bDistribution among clinical groups differs, P<0.05, Kruskal–Wallis
non-parametric rank test for contingency table data.cDistribution among clinical groups differs, P<0.001, Kruskal–Wallis non-parametric rank test for contingency table data. (Values in rows may not
equal 100% due to rounding; unilateral data were symmetrical, therefore only values from right side are included.)
Weakness in myositis 137
extensors, whereas subjects with 89% of the maximum summed
MMT grades could complete the task. Siegel et al.  showed the
number of lower extremity muscles with an MMT grade of <7 out
of 10 predicted walking speed in patients with juvenile IIM.
Our JDM patients were relatively high functioning and did not
exhibit any lower extremity median MMT grades <7 out of 10.
However, our patients with DM or PM exhibited median MMT
grades of ?7 or ?5 out of 10, respectively, for the hip muscle
groups, indicating considerable weakness. The increased proximal
weakness observed at all three hip muscles in patients with PM
compared with DM may reflect a critical threshold of function
and may partially explain why our patients with PM scored lower
on functional performance measures.
Although this is the largest study of specific patterns of
weakness in IIM clinical groups using a standardized approach
to assessing strength, there are limitations. This study included
MMT data obtained from patients over a wide range in age,
including four participants with JDM between 4.6 and 7 yrs of age
and five patients between 7 and 8 yrs of age. Some investigators
[28, 43] have cautioned against administering the MMT to
patients <5 or 6 yrs of age. Complications encountered in the
strength assessment of very young subjects may be related to levels
of attention, motivation and comprehension during testing .
In a study featuring 825 children with myelomeningocoel,
McDonald and colleagues  reported that serial MMT
examinations yielded stable results in participants older than
5 yrs of age. Our investigation featured only three subjects aged
5 yrs old or younger. In addition, our paediatric therapists did not
encounter any patients in this study in which MMT findings were
affected by subject cooperation or behaviour.
We found significant association among the functional
measures and the proximal MMT subscore, but our regression
analyses did not provide any additional insights regarding the
relationship of clinical course variables with the magnitude of
weakness. It should be noted, however, that disease duration was
greater in patients with PM compared with DM, which may have
had an influence on the greater degree of proximal weakness seen
in this clinical group. Additional study will be needed to better
understand the relationship among weakness, functional perfor-
mance and extra-musculoskeletal disease features. Also, different
physical therapists tested the adult and paediatric patients.
Nonetheless, we believe that use of multiple physical therapists
had minimal impact on results based on prior examiner training
and our observation of good inter-rater reliability of summed
MMT scores .
It is important to note that a general limitation of MMT is that
it is unable to distinguish between strength impairments that result
from disease activity vs disease damage . IMACS and PRINTO
have recognized the constraints of MMT as a primary therapeutic
trial outcome and have recommended incorporating a physician
global disease activity assessment to augment this core set measure
[5, 6]. Finally, our reported findings regarding the distribution
and severity of muscle weakness in our cohort of patients with
IIM are constrained by our selection of muscle groups to include
in the MMT. The results of our study do not suggest that other
muscle groups not included in our MMT do not contribute to
the functional limitations and disability observed in this patient
population or that our entire group of muscles tested is
recommended for inclusion in routine clinical testing or clinical
In conclusion, our study provides the most detailed account of
weakness in a cohort of patients with IIM. These findings suggest
that PM is associated with greater proximal and lower extremity
weakness than DM and JDM, and muscle groups are affected
symmetrically across IIM groups. In addition, we have identified
the five weakest muscle groups across IIM clinical groups, which
may serve to influence the selection of end-points in future
therapeutic trials and the targets of exercise intervention.
The authors thank Dr Maria Villalba and Dr Elizabeth Adams for
their contributions to this work. We also thank Ms Earllaine
Croarkin and Dr Mark Gourley for their critical reading of
the manuscript. The opinions and information contained in this
article are those of the authors and do not necessarily reflect those
of the National Institutes of Health or the United States Public
Funding: This work was supported in part by the Intramural
Research Program of the National Institutes of Health, National
Institute of Environmental Health Sciences, National Institute of
Arthritis and Musculoskeletal and Skin Diseases, Rehabilitation
Medicine Department and the NIH Clinical Center.
Disclosure statement: The authors have declared no conflicts of
Supplementary data are available at Rheumatology Online.
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Rheumatology key messages
? The magnitude of weakness differs among IIM clinical groups, with
PM weakest, adult DM intermediate and JDM strongest.
? Hip flexors, hip extensors, hip abductors, neck flexors and
shoulder abductors are the muscle groups with the greatest
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