Acquired immune and inflammatory myopathies: pathologic classification

We discuss pathology-based characterization and classification of acquired immune and inflammatory myopathies (IIMs).

Several types of IIMs do not fit well into the typical IIM subclassifications: dermatomyositis, polymyositis and inclusion body myositis (IBM). Myopathologic features that can provide additional diagnostic clarification in IIM are types of muscle fiber pathology; immune changes (cellular and humoral); and tissues with distinctive involvement (connective tissue, vessels and muscle fibers). Pathologic classification categories include immune myopathies with perimysial pathology (IMPP), a group that can be associated with antisynthetase antibodies; myovasculopathies, including childhood dermatomyositis; immune polymyopathies, active myopathies with little inflammation such as the myopathy with signal recognition particle antibodies; immune myopathies with endomysial pathology (IM-EP), illustrated by brachio-cervical inflammatory myopathy (BCIM); histiocytic inflammatory myopathies, like sarcoid myopathy; and inflammatory myopathies with vacuoles, aggregates and mitochondrial pathology (IM-VAMP), which have inclusion body myositis as a pathologic subtype and are poorly treatable. Some myopathologic features, like B-cell foci and alkaline phosphatase staining of capillaries or perimysium, are more likely to be present in treatable categories of IIM.

Myopathology can be used to classify IIM. Identification of distinctive myopathologic changes in IIM can improve diagnostic and prognostic accuracy and focus treatment, therapeutic trials and studies of pathogenic factors.