Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose:
In patients with idiopathic inflammatory myopathies (IIM) persisting muscle impairment after treatment underscores the need for improved management. Inadequate classification criteria for IIM are a fundamental limitation in clinical studies of myositis. An international, multidisciplinary collaboration, the International Myositis Classification Criteria Project (IMCCP), with support from ACR and EULAR, seeks to develop and validate new classification criteria for adult and juvenile IIM and its major subgroups.
Methods:
Identification and definition of potential criterion
Candidate variables to be included in classification criteria were assembled from published criteria and inclusion criteria in controlled trials of myositis and refined using Nominal Group Technique. Effort was made to assure content validity. Comparator groups confused with IIM were defined.
Data collection
Within this retrospective case control study, clinical and laboratory data from IIM and comparator patients were collected from 47 rheumatology, dermatology, neurology and pediatrics clinics worldwide from 2008-2011.
Analysis
Crude pair-wise associations among all variables measured and between each variable and clinician’s diagnosis were assessed. Three approaches for derivation of classification criteria were explored:
1. Traditional: case defined by specified number of items from a set
2. Risk score: patient assigned a probability risk score by summing score-points associated with the variables (Model 1)
3. Classification tree: case defined by a decision tree (Model 2)
A random forest algorithm explored the most important variables. Results obtained with each approach were utilized to improve others iteratively.
Validation
Internal validation using bootstrap methods was performed.
Results:
Data from 973 IIM (74% adults; 26% children) patients and 629 comparators (81% adults; 19% children) were obtained, representing subgroups of IIM (245 polymyositis, 239 dermatomyositis, 176 inclusion body myositis and 246 juvenile dermatomyositis cases). The comparators include other myopathies and systemic rheumatic diseases.
Two models were developed (Table). Model 1 performs better than Model 2 although both models perform equally to, or better, than current published criteria.
Conclusion:
New classification criteria for IIM with easy-to-access measurements and symptoms have been developed that generally have superior performance compared to existing criteria. External validation is in progress.
Table. New models for classification criteria for IIM and performance of criteria
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MODEL 1. RISK SCORE
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Variable |
Score points |
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18 ≤ Age of onset of first symptom < 40 |
1.6 |
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Age of onset of first symptom ≥ 40 |
2.3 |
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Clinical Muscle Variables |
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Objective symmetric weakness, usually progressive, of the proximal upper extremities |
0.7 |
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Objective symmetric weakness, usually progressive, of the proximal lower extremities |
0.6 |
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Neck flexors are relatively weaker than neck extensors |
1.6 |
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In the legs proximal muscles are relatively weaker than distal muscles |
1.5 |
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Skin Variables |
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Heliotrope rash |
3.3 |
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Gottronxs papules |
2.3 |
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Gottron’s sign |
3.4 |
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Other Clinical Variables |
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Dysphagia or esophageal dysmotility |
0.7 |
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Laboratory Variables |
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Serum creatine kinase (CK) activity |
1.2 |
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Anti-Jo-1 (anti-His) antibodies |
4.2 |
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Score-sum from above items* |
0.9 |
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Muscle Biopsy Variables |
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Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibers |
1.6 |
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Perimysial and/or perivascular infiltration of mononuclear cells |
1.1 |
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Perifascicular atrophy |
1.7 |
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* When muscle biopsies are available, multiply the score-sum of all other variables by 0.9 and then add the scores of the positive biopsies. |
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MODEL 2. CLASSIFICATION TREE
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(a) Heliotrope rash: If yes then IIM; if no go to step (b) (b) Objective symmetric weakness, usually progressive, of the proximal lower extremities: If yes then go to step (c); if no go to step (h) (c) Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibers: If yes then IIM; if no go to step (d) (d) Perimysial and/or perivascual infiltration of mononuclear cells: If yes then IIM; if no go to step (e) (e) Serum alanine aminotransferase activity: If yes then IIM; if no go to step (f) (f) Interstitial lung disease: If yes then IIM; if no go to step (g) (g) Dysphagia or esophageal dysmotility: If yes then IIM; if no then not IIM (h) Mechanic’s hands: If yes then IIM; if no go to step (i) (i) Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibers: If yes then IIM; if no then not IIM
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PERFORMANCE OF NEW AND EXISITING CLASSIFICATION / DIAGNOSTIC CRITERIA FOR IIM
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Performance (%) |
Model 1 Risk Score a |
Model 2 Tree |
Peter & Bohan [1]b |
Tanimoto et al. [2] |
Targoff et al. [3]b |
Dalakas & Hohlfeld [4]b |
Hoogendijk et al. [5]b |
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Without muscle biopsy data |
With muscle biopsy data |
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Sensitivity Specificity Positive predictive value Negative predictive value Correctly classified
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91 82 90 84 88 |
94 85 93 87 91 |
93 74 91 80 88 |
98 55 85 90 86 |
96 31 80 72 79 |
93 88 95 84 91 |
6 99 92 43 45 |
51 96 96 57 70 |
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a Cut point for probability: 50% b Definite and probable polymyositis and dermatomyositis |
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REFERENCES |
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1. Bohan A, Peter JB. Polymyositis and dermatomyositis: parts 1 and 2. N Engl J Med 1975, 292:344-347, 403-407. 2. Tanimoto K, Nakano K, Kano S, Mori S, Ueki H, Nishitani H, Sato T, Kiuchi T, Ohashi Y. Classification criteria for polymyositis and dermatomyositis. J Rheumatol 1995, 22:668-674. 3. Targoff IN, Miller FW, Medsger TA, Oddis CV. Classification criteria for the idiopathic inflammatory myopathies. Curr Opin Rheumatol 1997, 9:527-535. 4. Dalakas M, Hohlfeld R. Polymyositis and dermatomyositis. Lancet 2003, 362:971-982. 5. Hoogendijk JE, Amato AA, Lecky BR, Choy EH, Lundberg IE, Rose MR, Vencovsky J, de Visser M, Hughes RA. 119th ENMC international workshop: trial design in adult idiopathic inflammatory myopathies, with the exception of inclusion body myositis, 10-12 October 2003, Naarden, The Netherlands. Neuromuscul Disord 2004, 14:337-345. |
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Disclosure:
A. Tjärnlund,
None;
M. Bottai,
None;
L. G. Rider,
None;
V. P. Werth,
None;
C. A. Pilkington,
None;
M. de Visser,
None;
L. Alfredsson,
None;
A. A. Amato,
None;
R. J. Barohn,
None;
M. H. Liang,
None;
J. A. Singh,
research and travel grants from Takeda, Savient, Wyeth and Amgen,
2,
J.A.S. has received speaker honoraria from Abbott,
,
; aConsultant fees from URL pharmaceuticals, Savient, Takeda, Ardea, Allergan and Novartis.,
5;
F. W. Miller,
None;
I. E. Lundberg,
None;
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