The European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIMs)
| When no better explanation for the symptoms and signs exists, these classification criteria can be used | |||
| Variable | Score points | Definition | |
| Without muscle biopsy | With muscle biopsy | ||
| Age of onset | |||
| Age of onset of first symptom assumed to be related to the disease ≥18 years and <40 years | 1.3 | 1.5 | 18≤Age (years) at onset of first symptom assumed to be related to the disease <40 |
| Age of onset of first symptom assumed to be related to the disease ≥40 years | 2.1 | 2.2 | Age (years) at onset of first symptom assumed to be related to the disease ≥40 |
| Muscle weakness | |||
| Objective symmetric weakness, usually progressive, of the proximal upper extremities | 0.7 | 0.7 | Weakness of proximal upper extremities as defined by manual muscle testing or other objective strength testing, which is present on both sides and is usually progressive over time |
| Objective symmetric weakness, usually progressive, of the proximal lower extremities | 0.8 | 0.5 | Weakness of proximal lower extremities as defined by manual muscle testing or other objective strength testing, which is present on both sides and is usually progressive over time |
| Neck flexors are relatively weaker than neck extensors | 1.9 | 1.6 | Muscle grades for neck flexors are relatively lower than neck extensors as defined by manual muscle testing or other objective strength testing |
| In the legs, proximal muscles are relatively weaker than distal muscles | 0.9 | 1.2 | Muscle grades for proximal muscles in the legs are relatively lower than distal muscles in the legs as defined by manual muscle testing or other objective strength testing |
| Skin manifestations | |||
| Heliotrope rash | 3.1 | 3.2 | Purple, lilac-coloured or erythematous patches over the eyelids or in a periorbital distribution, often associated with periorbital oedema |
| Gottron’s papules | 2.1 | 2.7 | Erythematous to violaceous papules over the extensor surfaces of joints, which are sometimes scaly. May occur over the finger joints, elbows, knees, malleoli and toes |
| Gottron’s sign | 3.3 | 3.7 | Erythematous to violaceous macules over the extensor surfaces of joints, which are not palpable |
| Other clinical manifestations | |||
| Dysphagia or oesophageal dysmotility | 0.7 | 0.6 | Difficulty in swallowing or objective evidence of abnormal motility of the oesophagus |
| Laboratory measurements | |||
| Anti-Jo-1 (anti-histidyl-tRNA synthetase) autoantibody present | 3.9 | 3.8 | Autoantibody testing in serum performed with standardised and validated test, showing positive result |
| Elevated serum levels of creatine kinase (CK)* or lactate dehydrogenase (LD)* or aspartate aminotransferase (ASAT/AST/SGOT)* or alanine aminotransferase (ALAT/ALT/SGPT)* | 1.3 | 1.4 | The most abnormal test values during the disease course (highest absolute level of enzyme) above the relevant upper limit of normal |
| Muscle biopsy features—presence of: | |||
| Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibres | 1.7 | Muscle biopsy reveals endomysial mononuclear cells abutting the sarcolemma of otherwise healthy, non-necrotic muscle fibres, but there is no clear invasion of the muscle fibres | |
| Perimysial and/or perivascular infiltration of mononuclear cells | 1.2 | Mononuclear cells are located in the perimysium and/or located around blood vessels (in either perimysial or endomysial vessels) | |
| Perifascicular atrophy | 1.9 | Muscle biopsy reveals several rows of muscle fibres, which are smaller in the perifascicular region than fibres more centrally located | |
| Rimmed vacuoles | 3.1 | Rimmed vacuoles are bluish by H&E staining and reddish by modified Gomori trichrome stains | |
*Serum levels above the upper limit of normal.