EULAR/ACR 2017 Classification Criteria for Idiopathic Inflammatory Myopathies

Lundberg IE, Tjärnlund A, Bottai M, et al. — Ann Rheum Dis / Arthritis Rheumatol, 2017 (International Myositis Classification Criteria Project)

Purpose
Probability-based classification of adult and juvenile IIM (including dermatomyositis and amyopathic DM) for research and trials, with a tree for subgroup assignment.
Population
Patients in whom IIM is suspected and no better explanation exists. The score can be used without muscle biopsy when a pathognomonic DM rash is present; without rash, a muscle biopsy is required.
Formula
Score = sum of item weights. Probability of IIM = 1 / [1 + exp(5.33 − score)] without biopsy, or 1 / [1 + exp(6.49 − score)] with biopsy.
Cut-offs
Not IIM < 50 % (score < 5.3 / < 6.5 with biopsy) · Possible 50–< 55 % · Probable ≥ 55 % (≥ 5.5 / ≥ 6.7) · Definite ≥ 90 % (≥ 7.5 / ≥ 8.7). Sensitivity 87 % / specificity 82 % without biopsy; 93 % / 88 % with biopsy, at the 55 % cut-off.
⚙️ Data set and age at onset
Points: < 18 y = 0 · 18–< 40 y = 1.3 (1.5 with biopsy) · ≥ 40 y = 2.1 (2.2 with biopsy)
📝 Classification criteria items

Select every item present. Weights are shown for the selected data set (without / with biopsy).

Aggregate score 0.0
Probability of IIM —
🌳 Subclassification tree — additional item

Used only to assign the subgroup once IIM is classified (probability ≥ 55 %). The skin items and muscle weakness items above also feed the tree.

📚 References
  1. Lundberg IE, Tjärnlund A, Bottai M, et al. 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups. Ann Rheum Dis. 2017;76(12):1955–64 / Arthritis Rheumatol. 2017;69(12):2271–82.
  2. Bottai M, Tjärnlund A, Santoni G, et al. EULAR/ACR classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups: a methodology report. RMD Open. 2017;3(2):e000507.
  3. Lundberg IE, Tjärnlund A, Bottai M, et al. Response to: '2017 EULAR/ACR classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups: little emphasis on autoantibodies, why?' Ann Rheum Dis. 2018;77(9):e64.
  4. Schlecht N, Sunderkötter C, Niehaus S, Nashan D. Update on dermatomyositis in adults. J Dtsch Dermatol Ges. 2020;18(9):995–1013.
Clinical decision support only. This tool is intended to assist clinical assessment and does not replace professional judgment. Always interpret results in the context of the individual patient.