Immunopathological features of myopathy associated with small-to-medium-sized vessel vasculitis and differences from...

Patients with systemic vasculitis may develop myalgia as an initial symptom. However, the immunopathology of vasculitic myopathy remains unclear. We investigated the immunopathological features of skeletal muscle in small-to-medium-sized vessel vasculitis.

We analysed muscle tissue biopsies from 15 patients with vasculitis, including antineutrophil cytoplasmic antibodyassociated vasculitis and polyarteritis nodosa, and 15 patients with autoimmune myositis (AIM), including polymyositis and immune-mediated necrotising myopathy, as comparison disease controls. Immunohistochemical staining for CD56/neural cell adhesion molecule (NCAM), major histocompatibility complex class I, C5b-9/membrane attack complex (MAC), and CD31 was performed. The vascularity score was defined as the total number of CD31-expressing blood vessels. The association between CD56/NCAM-expressing myofibers and clinical findings was evaluated in patients with vasculitis.

Patients with vasculitis had a significantly lower frequency of CD56/NCAM-expressing myofibers than those with AIM and a positive correlation between the frequency of CD56/NCAM-expressing myofibers and serum aldolase levels. Patients with vasculitis had significantly fewer major histocompatibility complex class I-expressing myofibers and C5b-9/MAC deposits on the sarcolemma than those with AIM. C5b-9/MAC deposits in blood vessels were observed in >70% of patients with vasculitis. Patients with vasculitis had significantly higher vascularity scores in the endomysium than those with AIM.

Patients with vasculitis demonstrated mild myofiber damage based on the lower involvement of CD56/NCAM-expressing myofibers compared to those with AIM. Complement component deposits on the vessel walls and hypervascularity in the endomysium areas may be immunopathological features of vasculitic myopathy.