Criteria
The European League Against Rheumatism and American College of Rheumatology (EULAR/ACR) classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIMs)[123]
Partially validated criteria for diagnosis of 'definite', 'probable', and 'possible' IIM; and the major subgroups of IIM, including DM, amyopathic DM, and juvenile DM.
Points are allocated as follows for different variables, with or without muscle biopsy.
An online scoring calculator is available: Classification criteria for IIMs Opens in new window
Age of onset
Age of onset of first symptom assumed to be related to the disease ≥18 years and <40 years
With muscle biopsy: 1.3
Without muscle biopsy: 1.5
Age of onset of first symptoms assumed to be related to the disease ≥40 years
With muscle biopsy: 2.1
Without muscle biopsy: 2.2
Muscle weakness
Objective symmetric weakness, usually progressive, of the proximal upper extremities
With muscle biopsy: 0.7
Without muscle biopsy: 0.7
Objective symmetric weakness, usually progressive, of the proximal lower extremities
With muscle biopsy: 0.8
Without muscle biopsy: 0.5
Neck flexors are relatively weaker than neck extensors
With muscle biopsy: 1.9
Without muscle biopsy: 1.6
In the legs, proximal muscles are relatively weaker than distal muscles
With muscle biopsy: 0.9
Without muscle biopsy: 1.2
Skin manifestations
Heliotrope rash
With muscle biopsy: 3.1
Without muscle biopsy: 3.2
Gottron's papules
With muscle biopsy: 2.1
Without muscle biopsy: 2.7
Gottron's sign
With muscle biopsy: 3.3
Without muscle biopsy: 3.7
Other clinical manifestations
Dysphagia or oesophageal dysmotility
With muscle biopsy: 0.7
Without muscle biopsy: 0.6
Laboratory measures
Anti-histidyl-tRNA synthetase (anti-Jo-1) autoantibody present
With muscle biopsy: 3.9
Without muscle biopsy: 3.8
Elevated serum levels of creatine kinase or lactate dehydrogenase or aspartate aminotransferase or alanine aminotransferase
With muscle biopsy: 1.3
Without muscle biopsy: 1.4
Additional points are allocated as follows if muscle biopsy features the presence of:
Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibres: 1.7
Perimysial and/or perivascular infiltration of mononuclear cells: 1.2
Perifascicular atrophy: 1.9
Rimmed vacuoles: 3.1.
Scoring
Probability of IIM including muscle biopsy = 1/[1+exponential (5.33–score)] or
Probability of IIM without muscle biopsy = 1/[1+exponential (6.49–score)]
≥50% and <55% = possible IIM
≥55% and <90% = probable IIM
≥90% = definite IIM.
Patients classified with IIM by the EULAR/ACR classification criteria can be further subclassified using a classification tree that includes:
Amyopathic DM
DM
Inclusion body myositis
Immune-mediated necrotising myopathy
Juvenile DM
Polymyositis.
Commonly used severity criteria for idiopathic inflammatory myopathies
Severe disease: includes those with severe muscle weakness (e.g., quadriplegia), interstitial lung disease, myocarditis, respiratory failure, severe dysphagia, or other life-threatening complications.
Non-severe disease: includes those with muscle strength of ≥4/5 and none of the life-threatening complications of severe disease.
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