New System Classifies Idiopathic Inflammatory Myopathies

By Will Boggs MD

September 14, 2018

NEW YORK (Reuters Health) - A new classification system would separate idiopathic inflammatory myopathies (IIM) into four clusters based on clinical features and myositis-specific autoantibodies.

Historically separated into dermatomyositis (DM) and polymyositis (PM), IIM now also includes inclusion body myositis (IBM) and immune-mediated necrotizing myopathy (IMNM). Increasing evidence supports a link between myositis-specific autoantibodies (MSA) and different types of IIM.

Dr. Kuberaka Mariampillai from APHP Paris, Groupe Hospitalier Pitie-Salpetriere, in Paris, France, and colleagues used 47 selected variables from 260 patients in the French myositis registry to construct a new classification system for IIM.

Unsupervised multiple correspondence analysis and hierarchical clustering analysis aggregated patients into four subgroups that differed in clinical features and MSA, the team explains in JAMA Neurology, online September 10.

Cluster 1 included patients who were male, white and older than 60 years and who had finger flexor and quadriceps weakness, along with findings of vacuolated fibers and mitochondrial abnormalities. This group corresponded to the diagnosis of IBM.

Cluster 2, which corresponded to IMNM, included patients who were women and who had high creatine phosphokinase levels, necrosis without inflammation and anti-SRP (signal recognition particle) or anti-HMGCR (3-hydroxy-3-methylglutaryl-coenzyme A reductase) antibodies.

Patients with dermatomyositis fell into Cluster 3, which included patients with dermatomyositis rash and anti-Mi2 (complex nucleosome remodeling histone deacetylase) or anti-TIF1y (transcription intermediary factor-1y) antibodies.

Finally, Cluster 4, corresponding to antisynthetase syndrome (ASA), was defined by the presence of anti-Jo1 (histidyl-ARN-t-synthetase) or anti-PL7 (threonine-ARN-t-synthetase) antibodies.

"The decisional algorithm showed that MSA played a key role in estimating the connection to a cluster, whereas the pathologic data were dispensable," the researchers conclude. "These findings suggest the association of this new classification with prognosis, and new therapeutic approaches in IIM warrants further study."

Dr. Mazen M. Dimachkie from the University of Kansas Medical Center, in Kansas City, who recently reviewed the pathogenesis and treatment of inclusion body myositis, told Reuters Health by email, "This is an interesting and important retrospective study in a large number of French myositis cases, with heterogeneity as to the extent of antibody testing."

"Before adoption in clinical care, it is important to validate this classification prospectively in a multicenter, international cohort with more comprehensive and more methodologically robust antibody testing," said Dr. Dimachkie. "However, my sense is that antibody testing provides added value in the diagnosis and management of myositis that complements other established diagnostic testing, particularly in DM, IMNM and ASA cases."

Dr. Mariampillai did not respond to a request for comments.


JAMA Neurol 2018.