Diagnostic Evaluation of Immune-Mediated Myopathies

Abstract

The inflammatory myopathies (IM) constitute a heterogeneous group of acquired myopathies that have in common the presence of endomysial inflammation and/or express markers of inflammatory myopathy. Based on steadily evolved clinical, histological, and immunopathological features and some autoantibody associations, they can be classified. Each inflammatory myopathy subset has distinct immunopathogenesis, prognosis, and response to immunotherapies, necessitating the need to correctly identify each subtype from the outset to avoid disease mimics and proceed to early therapy initiation. The diagnosis of IM is based on the combination of clinical history including the pattern of muscle involvement and tempo of disease progression (as described above), combined with the determination of serum muscle enzymes, muscle biopsy findings, and at times autoantibodies. Ancillary information is provided by electromyography, which can be useful to exclude neurogenic conditions or assess disease activity. Muscle MRI with contrast can reveal edema and inflammation in muscle and fascia and is mainly useful to define and assess the distribution of atrophic muscles.