C4d as a marker of complement activation in dermatomyositis muscle tissue

Aim: To study C4d expression as a marker of complement activation in the diagnosis of dermatomyositisMaterial and Methods: Muscle biopsies from patients diagnosed as definite dermatomyositis (10), nonspecific myositis associated with connective tissue disease (9), necrotizing autoimmune myositis (1), inclusion body myositis (1), and normal muscle (1) according to European Neuromuscular criteria 2004 were studied for C4d expression and capillary loss on CD 34 immunohistochemistry.Results: C4d was expressed in all biopsies of definite dermatomyositis in the perimysial vessels and in 3/10 endomysial capillaries corresponding to capillary loss on CD 34.C4d expression was seen in 2/3 perimysial and endomysial vessels in nonspecific myositis (2/3 overlap myositis), and 1/1 of nectrotizing autoimmune myositis.Necrotic muscle fibers in all biopsies showed positivity irrespective of the diagnosis.Conclusion: C4d can be used as a marker of complement activation for the diagnosis of dermatomyositis.