Comparison between treatment naive juvenile and adult dermatomyositis muscle biopsies: difference of inflammatory cells phenotyping

Background: Different inflammatory cells (i.e., CD4, CD8, CD20 and CD68) are involved in pathogenesis of DM muscle. In this context, the aim of this study was to assess and compare these inflammatory cell phenotyping in muscle samples of treatment naive juvenile and adult patients with dermatomyositis. Methods: This is a cross-sectional study, in which 28 untreated juvenile and 28 adult untreated dermatomyositis patients were included. Immunohistochemical analysis was performed on serial frozen muscle sections. Inflammatory cell phenotyping was analyzed quantitatively in endomysium, perimysium, and perivascular (endomysium and perimysium) area. Results: Mean age at disease onset was 73 and 42.0 years in juvenile and adult dermatomyositis, respectively. Both groups had comparable time duration from symptom's onset to biopsy performance. CD4 and CD8 positive cells distributions were similar in both groups in all analyzed area, except for more predominance of CD4 in perimysium at juvenile muscle biopsies. The CD20 and CD68 positive cells were predominantly observed in adult muscle biopsy sections, when compared to juvenile samples, except for similar distribution of CD20 in perivascular endomysium, and CD68 in perimysium. Conclusions: These data show that the differences between juvenile and adult dermatomyositis may be restricted not only to patients' age, but also to different inflammatory cell distribution, particularly, in new-onset disease. Further studies are necessary to confirm the present study data and to analyze meaning of the different inflammatory cell phenotyping distribution finding in these both diseases.