Table 1.

Summary of Measures of Disease Activity in Myositis

Name of measure/scale	Purpose/ content	Method of administration	Respondent burden	Administration burden	Interpretation of scores	Reliability evidence	Validity evidence	Ability to detect change	Strengths	Cautions
Physician Global Activity	Overall rating of myositis disease activity based on all clinical and laboratory measures available at the time of assessment	Clinician completed	Not applicable	< 1 minute, but time to assess the patient. Hand scored	On 10-cm VAS, 0 = inactive disease, 10 = extremely severe disease activity. On a Likert scale, 0 = inactive, 1 = mild activity, 2 = moderate activity, 3 = severe activity, 4 = extremely severe activity	Excellent internal consistency and inter-rater reliability	Excellent content and construct validity	Excellent responsiveness. ≥ 20% improvement is consensus of clinically meaningful change	Measures important concept, good psychometric properties, appropriate for clinical and research use, most validated in juvenile DM/PM with some validity in adult DM/PM	Somewhat subjective and based on the experience of the rater. Reliability of serial ratings dependent on examining previous scores. Not validated for IBM
Patient or Parent Global Activity	Overall rating of myositis disease activity	Patient or parent self- report	< 1 minute	< 1 minute. Hand scored	On 10 cm VAS, 0 = inactive disease, 10 = extremely severe disease activity. On a Likert scale, 0 = inactive, 1 = mild activity, 2 = moderate activity, 3 = severe activity, 4 = extremely severe activity	Ratings distinct from physician ratings. Reliability not available for patient/parent global activity	Good construct validity	Excellent responsiveness. ≥ 20% improvement is consensus of clinically meaningful change	Measures important concept, good psychometric properties, appropriate for clinical and research use, most validated in juvenile DM/PM with some validity in adult DM/PM	Somewhat subjective and based on the experience of the rater. Reliability of serial ratings dependent on examining previous scores. Not validated for IBM
Manual Muscle Testing(MMT)	Measures muscle strength by application of pressure to muscle groups tested against gravity or through a range of motion for muscle groups with less than anti-gravity strength	Administered by a trained clinician/physical therapist	Takes 30–60 minutes to assess 24 26 muscle groups. Takes < 5 minutes to assess 8 key muscle groups. May be demanding for weak child or younger children with limited ability to cooperate	Takes 30–60 minutes to assess 24–26 muscle groups. Takes < 5 minutes to assess 8 key muscle groups. Hand scoring < 1 minute	Modified MRC or Kendall 0–10 scales used. Scores may be 0–260 for a total score of 12 proximal and distal muscle groups tested bilaterally + 2 axial muscle groups, 0–80 for MMT8	Excellent internal consistency, test-retest reliability, very good intra- rater reliability. Reliability of scores much better than of individual muscle groups	Good content validity for MMT8. Good construct validity	Excellent responsiveness. ≥ 15% improvement in MMT score in adult DM/PM and ≥ 18% improvement for juvenile IIM is consensus for clinically important improvement	Measures concept central to the assessment of myositis patients. Sound psychometric properties. Appropriate for clinical and research use. Validated in adult and juvenile DM/PM. Does not require special equipment	Requires training in administration of the test. Widely used but not validated in IBM. Total MMT is lengthy for clinical setting. Does not distinguish activity from damage. Patients with muscle atrophy may not be sensitive to change
Health Assessment Questionnaire (HAQ)/Childhood Health Assessment Questionnaire (CHAQ)	Assess physical function in 9 (HAQ) or 8 (CHAQ) domains of daily activities	Self-or proxy- administered	Minimal	Minimal	Range 0–3 0=no or mild physical dysfunction, <0.125–0.25= mild physical dysfunction, >1.0= moderate to severe disability	Test-retest reliability excellent in children. Internal consistency acceptable for juvenile myositis. Intra-rater reliability not available in myositis	Construct validity excellent in children. Some evidence supportive in adult DM/PM. No assessment of content validity in myositis. Limited criterion validity in adult DM/PM	Responsiveness good to excellent in children with recognized change. Data not available for adults	Brief and easy to use. Takes little time. Good psychometrics in children with myositis	Significant floor effect. Limited validity in adult DM/PM, no validity in IBM
Childhood Myositis Assessment Scale(CMAS)	Assess muscle strength, physical function, and endurance	Observational, performance based, administered by clinician or therapist	15–20 minutes. May be demanding for weak child or younger children with limited ability to cooperate	15–20 minutes to administer, <1 minute to score	Range 0–52. Higher scores indicate greater strength or physical function. <15=severe weakness (consensus) >48=normal >45=mild impairment >39=mild to moderate >30= moderate impairment (based on comparison with CHAQ)	Test-retest and Inter- rater reliability very good to excellent. Internal consistency not available	Strong evidence for construct validity. Content validity not assessed	Responsiveness strong in children with recognized change.	Comprehensive assessment which specifically addresses endurance. Reduction in bias and non- completion due to observational nature. Good psychometric properties in juvenile IIM.	Requires training to administer. Time needed to administer may limit usefulness clinically. Significant ceiling effect. Currently validated only for juvenile IIM and not studied yet in adult myositis subgroups.
Myositis Disease Activity Assessment Tool (MDAAT)	Assess 6 extra- muscular organs, to produce a global extra- muscular score, and the muscle score, which gives a total disease activity index score	Clinician completed	Not applicable	Time to complete a history and physical examination (likely 15–30 minutes). Hand or computer scored	For MYOACT organ system score, scored on 10-cm VAS, 0 = inactive disease, 10 = extremely severe disease activity. For MYOACT each item is answered 0 = not present; 1= improving; 2 = the same; 3 = worse; 4 = new, and converted to organ system scores of A-E, based on the intention to treat. Scores range from 0–60 for the extramuscular MYOACT score and 0–70 for the total MYOACT score, and they range from 0–54 for the extra- muscular MITAX score and 0–63 for the total MITAX score	Excellent internal consistency, good inter- rater reliability	Excellent content validity, good construct validity	Excellent responsiveness. ≥ 20% improvement in the extra- muscular score is consensus of clinically meaningful change	Measures important concept, good psychometric properties, appropriate for clinical and research use, most validated in adult and juvenile DM	Somewhat cumbersome to use/score (needs training). MYOACT scores are somewhat subjective and based on the experience of the rater. For MYOACT scores, reliability of serial ratings dependent on examining previous scores. Not validated for IBM
Disease Activity Scale (DAS)	Evaluate muscle and skin involvement	Clinician completed	5 minutes	Hand calculated	Total score: 0–20, with higher score meaning higher disease activity. Skin subscale 0–9. Weakness sub scale 0–11	Good internal consistency, moderate to poor inter- rater reliability.	Good construct validity	Excellent responsivenss	Simplicity and good psychometric properties. Validation studies in juvenile DM.	Performance in clinical trials still to be evaluated. Not evaluated in other myositis subgroups.
Short Form 36 (SF-36)	Assessment of the global health- related quality of life, functional health and well-being	Self- administered	Minimal	Minimal. Scoring is by computer	The instrument consists of 36 items answered by marking from 2–6 options. Scoring ranges from 0–100, with 0 indicating maximum disability	Test-retest reliability and intra-rater reliability are not available in myositis	Good construct and criterion validity in DM and PM, with limited data in IBM. Content validity is unavailable in myositis	Statistics on responsiveness are not available in myositis	Widely used in other diseases, easily administered, available in multiple languages, with extensive normative data	Limited experience and validation in adult myositis. Costly license
Child Health Questionnaire (CHQ)	Evaluate physical and psychosocial well being	Parent or child administered	10–15 minutes	Computer score with proprietary algorithm	Summary score standard	No information available in juvenile DM	Good content validity, limited but good construct validity	Physical score moderately responsive	Measures important concept, psychometric properties sound, appropriate mainly for research use	Respondent burden. Complicated computer scoring system. Limited studies in juvenile DM.
Physician Global Damage	Overall rating of myositis disease damage based on all clinical and laboratory measures available at the time of assessment	Clinician completed	Not applicable	< 1 minute, but time to assess the patient. Hand scored	On 10-cm VAS, 0 = no damage, 10 = extremely severe damage. On a Likert scale, 0 = no damage, 1 = mild damage, 2 = moderate damage, 3 = severe damage, 4 = extremely severe damage	Excellent internal consistency and good inter-rater reliability	Good content and moderate to excellent construct validity	As expected, little responsiveness in < 1 year	Measures important concept, good psychometric properties, appropriate for clinical and research use, most validated in juvenile DM/PM with limited validity in adult DM/PM	Somewhat subjective and based on the experience of the rater. Reliability of serial ratings dependent on examining previous scores. Not validated for IBM, and needs additional validation for adult DM/PM
Myositis Damage Index (MDI)	Assessment of damage (persistent or permanent changes) using both VAS and present- absent scoring to assess 9 organ systems	Clinician completed	Not applicable	Time to complete a history and physical examination (likely 15–30 minutes). Hand or computer scored	For Severity of Damage, scores range 0–110. For each organ system score, scored on 10- cm VAS, 0 = inactive disease, 10 = extremely severe disease activity. For the Extent of Damage, items are scored present or absent. Total score is 0–35 in children, 0–37 in adolescents, and 0–38 in adults. A higher score indicates more damage	Good inter- rater reliability. Severity and extent of damage highly correlate	Good construct and criterion validity	Severity of Damage score increases slowly in adult DM/PM patients, as expected. Extent of Damage score shows detectable mild increase.	Measures important concept, sound psychometric properties, appropriate for research use in adult and juvenile DM/PM	Severity of Damage scores are somewhat subjective and based on the experience of the rater. For Severity of Damage scores, reliability of serial ratings dependent on examining previous scores. Not validated for IBM.
Quantitative Muscle Testing (QMT)	Measure amount of maximum isometric force using specialized equipment	Requires trained health care provider to conduct test	1 hour	1 hour	Values for each muscle group dependent on devices used, in kgs. Typically measure 8 or 12 muscle groups; total individual score for megascore	Good reliability in ALS trials and DMD; limited but good reliability in adult DM/PM.	Good but very limited construct validity in IBM	Can detect changes in strength, correlated with MMT and IBMFRS.SRM not available.	Quantitative measure – might be sensitive to small changes in strength or in measuring mild weakness	Requires specialized training, special hardware and software, costly. Patients must have at least anti- gravity strength to perform. Very limited validation in IBM and adult DM/PM
Myositis Functional Index 2 (FI-2)	Assess dynamic muscle endurance in 7 muscle groups	Observation of functional test	Not applicable	Takes maximum of 33 minutes to assess both right/left sides. Requires maximum of 21 minutes to assess dominant side. Takes 5 minutes to score by hand	Each muscle group is scored as the number of correctly performed repetitions, varying from 0–60 or 0 –120. No total score	Inter-and intra-rater reliability good to excellent	Good content validity. Ensured by moderate construct validity	Variable, limited data from one therapeutic trial.	Myositis- specific objective functional index which measures muscle endurance and repetition. Limited validation studies in adult DM and PM. Patients involved in the content validity process. Measures an important concept, muscle endurance	FI-2 is a new instrument requiring a long time to perform. Further validation needed for sensitivity to change and in other myositis subgroups. A training session is needed to ensure reliability. Administrative burden might limit feasibility for use in clinical practice and research.
Myositis Activities Profile (MAP)	Assess activity limitation, Activities of daily life. Contains 31 items divided into subscales	Self-reported questionnaire	5–10 minutes	5 minutes to score by hand	Subscales are scored as the median value of item responses within the subscale varying from 1 (no difficulty) to 7 (impossible). Single items are scored as the actual item response, 1–7.	Moderate test-retest reliability. Moderate to strong internal consistency	Good content validity. Moderate construct validity.	Variable, limited data from one therapeutic trial.	Myositis- specific measure of activities of daily living and functional disability. Limited validation studies in adult DM/PM. Patients involved in content validity process. Measures an important concept as to both difficulty and importance of activities. Low administrative and patient burden support use in clinical practice and research	New measure not yet published in languages other than Swedish. Further validation needed, including sensitivity to change, construct validity, consistency of items, and performance of the tool in other myositis subgroups
Inclusion Body Myositis Functional Rating Scale (IBMFRS)	10-point disease- specific functional rating scale	Interviewer patient; no special training required	15 minutes	15 minutes	10 items, each 0–4 grade; add individual items for total score. 0 = several functional disabilities, 40 = no functional disability or normal function	Not available in myositis	Moderate construct validity	Very responsive in a single therapeutic trial	Measures important elements of daily life functions that are often affected by the disease. Quick, inexpensive and easy to administer. IBM-specific measure	Responses based on function prior to start of disease; subjective measurements. Further validation needed.
Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI)	Measure several key features of skin activity and damage in DM	Clinician completed	None	Mean 4.8 minutes for experienced dermatologists, less than 1 minute to hand score.	Scores are divided into activity and damage, with scores ranging from 0–100 for activity and 0–32 for damage. The level of disease activity can be interpreted as low, moderate, or high. The mean CDASI activity for mild disease was 11.4 ± 7.0, moderate was 25.6 5± 8.9, and severe was > 39.4.	Good to excellent inter-and intra-rater reliability	Content validity adequate by participating dermatologists. Moderate to excellent construct validity	Responsiveness is strong in a group of patients with recognized change	Measures important components of skin activity and damage. Psychometric properties sound. Appropriate for clinical and research use. Partially validated in adult DM, including amyopathic DM.	Need appropriate training. Does not measure every aspect of DM disease, but focuses on elements in the skin likely to be responsive in the context of therapeutic interventions. Not validated in other myositis subgroups.
Cutaneous Assessment Tool (CAT)	Assess skin disease in both activity and damage domains	Examination- based tool, administered by clinician	May take up to 15 minutes, depending on patient complexity and assessor’s experience with DM skin disease. Abbreviated tool may be faster to complete	May take up to 15 minutes, but scoring takes <1 minute	Activity Score: range 0–96 ≤ 1=no activity 7=mild 13=moderate 18=severe 31=very severe. Damage Score: range 0–20 0=no damage 1=mild 2=moderate 5=severe or very severe	Total activity score has good internal consistency, test-retest and inter-rater reliability. Total damage score has fair- to-good internal consistency, test-retest and inter-rater reliability. Reliability of individual activity and damage items are more variable	Strong evidence for construct validity in juvenile IIM and more limited in adult DM. Content validity not assessed.	Responsiveness moderate to strong in children with juvenile DM with recognized change	Comprehensive assessment of relevant cutaneous lesions, including both activity and damage. Partially validated in juvenile IIM and adult DM	Requires training to administer. Some concerns about reliability of some items. Not validated in other myositis subgroups.
DM Skin Severity Index(DSSI)	Measure several key features of skin activity in DM	Clinician completed	None	2–3 minutes to use by experienced dermatologists, <1 minute to score	The total DSSI score can range from 0 to 72. Compared to the global physician score on a 0–10 VAS, the DSSI was 1.28 ±1.5 for mild global activity, 5.4±4.0 for moderate global activity, and 14.9 ± 14.1 for severe global activity	Good intra- rater reliability. Moderate to good inter- rater reliability. Good to excellent test- retest stability	Content validity was evaluated by a panel of experts. Moderate, but limited construct validity	SRM not available	Evaluates elements of skin disease activity of DM. Adapted from the PASI for psoriasis. Ease of use. Evaluated in adult DM and amyopathic DM	Body surface area may not be reliable or responsive to change. Does not assess skin damage. Not validated in other myositis subgroups.
Skindex-29 and Skindex-16	Measure of skin-specific QoL	Patient self- report. 3 subscales: emotions, symptoms, function	5 minutes	Scoring involves conversion to linear scale of 100, and then taking the mean of the patient’s responses in a given scale. Computer scoring	Norms, as well as correlation with QoL burden in a number of different skin diseases is available. Norms for disease severity are available	Excellent internal consistency and test-retest reliability in other skin diseases and adult DM	Moderate construct validity in DM and amyopathic DM. Content and criterion validity for other skin diseases, but not available for myositis	Not available for myositis	Widely used for autoimmune, inflammatory and non- inflammatory skin diseases. Skindex correlates more highly than the SF-36 scores with the patients’ reports of the condition of their skin. Captures emotional component of QoL well. Limited validity for adult DM and amyopathic DM.	Longer than some other skin-specific QoL measures. No validation in other myositis subgroups.
Dermatology Life Quality Index (DQLI)	Measure of skin-specific QoL	Patient self- report	2 minutes	Scoring takes less than 1 minute	Score range 0–30. Interpretation can be done by cut points: 0 (score of 0–1), no effect;1 (score of 2–5), small effect; 2 (score of 6–10), moderate effect;3 (score 11–20), very large effect;4 (score 21–30), extremely large effect	Not assessed in myositis	Moderate to low construct validity in DM and amyopathic DM. Content and criterion validity not established in myositis	Not established for myositis	Widely used for autoimmune, inflammatory and non- inflammatory skin diseases, short. Limited data in adult DM and amyopathic DM,	Focus on disability, response distribution has ceiling effects, and dimensionality and item bias are problems. Not yet studied in other myositis subgroups

Abbreviations: VAS = visual analog scale, DM = dermatomyositis, PM = polymyositis, IBM = inclusion body myositis, MRC = Medical Research Council, MMT = manual muscle testing, HAQ = Health Assessment Questionnaire, CHAQ = Childhood Health Assessment Questionnaire, IIM = idiopathic inflammatory myopathy, MYOACT = Myositis Disease Activity Assessment Visual Analog Scale, MITAX = Myositis Intention to Treat Activities Index, ALS = amytrophic lateral sclerosis, DMD = Duchenne muscular dystrophy, IBMFRS = Inclusion Body Myositis Functional Rating Scale, SRM = standardized response mean, PASI = Psoriasis Area and Severity Index, QoL = quality of life, SF-36 = Short Form 36