Fasciitis as a common lesion of dermatomyositis, demonstrated early after disease onset by en bloc biopsy combined with magnetic resonance imaging.

Objective To investigate whether fasciitis is histopathologically demonstrable in patients with dermatomyositis (DM), and to analyze the process of inflammatory progression in myopathy accompanying DM. Methods STIR or fat-suppressed T2-weighted magnetic resonance imaging (MRI) and en bloc biopsy were performed in 14 patients with newly diagnosed adult-onset DM. The severity of inflammatory cell infiltration around the fascial and intramuscular small blood vessels was evaluated using the total vascular inflammation score (TVIS). Results In all patients, MRI revealed abnormal hyperintensity in the fascia and in marginal sites of the muscle, predominantly over central sites. En bloc biopsy revealed the presence of fasciitis in most of the patients, as shown by inflammatory infiltrates around the fascial small blood vessels. In those patients who underwent en bloc biopsy earlier than 2 months after the appearance of muscle symptoms, the TVIS of the fascia was significantly higher than the TVIS of the muscle. In contrast, in those patients who underwent en bloc biopsy ≥2 months after muscle symptom onset, the TVIS of the fascia did not differ significantly from the TVIS of the muscle. Conclusion Fasciitis was histopathologically demonstrated in patients with newly diagnosed adult-onset DM as early as 2 months after the onset of muscle symptoms. These results indicate that fasciitis is a common lesion of DM and suggest that the fascial microvasculature is the primary site of inflammatory cell infiltration in DM. Fasciitis may contribute to muscle symptoms in patients with DM without myositis.