EULAR/ACR Classification in MDA5+ Myositis Patients Save
The diagnosis of idiopathic inflammatory myopathies (IIMs) can be informed by the 2017 EULAR/ACR classification criteria, but their utility in patients with clinically amyopathic dermatomyositis (CADM) and anti–melanoma differentiation–associated protein 5 (anti–MDA-5)–positive IIM is less certain. A current analysis suggests that nearly 30% of MDA5 IIM patients may be missed by the 2017 EULAR/ACR classification criteria for IIM.
A total of 120 consecutive adult patients diagnosed as having anti–MDA-5–positive IIM from 10 Hong Kong hospitals were studied. One-third (31.7%) had dermatomyositis, and two-thirds (68.3%) had CADM. An IIM diagnosis was found in 72% using EULAR/ACR criteria and 41% using Bohan and Peter criteria.
The sensitivity of the EULAR/ACR criteria could be improved to 98.3% if anti–MDA-5 antibody–positive status was considered as one of the criteria. The MSA-based criteria had 100% sensitivity. With modification of specific phenotypic-serologic criteria to capture classification of patients with anti–MDA-5 antibodies, 97.5% of patients were able to be classified as having IIM.
Studies have shown the EULAR/ACR criteria had a higher sensitivity (87.7%) compared to the Bohan and Peter (BP) criteria (80.4%) and that the EULAR/ACR criteria specificity was very high (>98%) for the major IIM subgroups polymyositis, dermatomyositis, and inclusion body myositis.
In a previous report it was shown that in myositis patients with MSAs, autoantibodies outperform the EULAR/ACR-defined myositis subgroups in predicting the clinical phenotypes of patients - suggesting that MSAs should be included in future revisions of the myositis classification scheme.
These authors suggest incorporating anti–MDA-5 antibody positivity as a criterion into existing or future criteria sets to diagnose patients with IIM.
The EULAR/ACR Classification Criteria for Adult and Juvenile Idiopathic Inflammatory Myopathies and their Major Subgroups
(suggested total aggregated score of score of ≥5.5 and ≤ 5.7 (≥6.7 and ≤ 7.6 if biopsy is available)
|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|
|Age of onset of first symptom assumed to be related to the disease ≥ 40 years||2.1||2.2|
|Objective symmetric weakness, usually progressive, of the proximal upper extremities||0.7||0.7|
|Objective symmetric weakness, usually progressive, of the proximal lower extremities||0.8||0.5|
|Neck flexors are relatively weaker than neck extensors||1.9||1.6|
|In the legs proximal muscles are relatively weaker than distal muscles||0.9||1.2|
|Other clinical manifestations|
|Dysphagia or esophageal dysmotility||0.7||0.6|
|Anti-Jo-1 (anti-histidyl-tRNA synthetase) autoantibody present||3.9||3.8|
|Elevated serum levels of creatine kinase (CK)* or lactate dehydrogenase (LDH)* or aspartate aminotransferase (ASAT/AST/SGOT)* or alanine aminotransferase (ALAT/ALT/SGPT)*||1.3||1.4|
|Muscle biopsy features- presence of:|
|Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibres||1.7|
|Perimysial and/or perivascular infiltration of mononuclear cells||1.2|