THU0241 Ethnic but not gender differences in disease manifestations in dermatomyositis patients
Authors: A. Tjärnlund, L. Rider, F. Miller, V.P. Werth, I.E. Lundberg
Journal: Annals of the Rheumatic Diseases (2012)

<h3>Background</h3> Dermatomyositis (DM) is a subset of idiopathic inflammatory myopathies (IIM), which are heterogeneous rheumatic disorders characterized by inflammation of skeletal muscle and progressive weakness. New and improved treatment is needed but a significant and fundamental problem for conducting clinical trials is the inadequate classification criteria for IIM. To address this, the International Myositis Classification Criteria Project (IMCCP) was established with the aim to develop and validate new classification criteria for IIM and major subgroups of IIM. Clinical and laboratory data from 1600 IIM and comparator cases have been collected. Dissimilarities in disease manifestations among different patient groups have to be considered as classification criteria must be uniformly valid. Little, however, is known about these differences in relation to clinical phenotype for IIM. <h3>Objectives</h3> The aim of this study was to investigate ethnic or gender differences in clinical manifestations in adult DM, juvenile DM (JDM) and amyopathic DM (ADM). <h3>Methods</h3> We extracted data on serology, 23 muscle variables (e.g., pattern of muscle weakness) and 14 skin manifestations from the IMCCP database and assessed their prevalence among 238 DM, 233 JDM and 45 ADM patients. Comparisons were made between genders and patients of Caucasian and Asian origin. <h3>Results</h3> Comparisons between the two ethnic groups revealed significant differences in clinical phenotypes. For adult DM cases, several muscle variables were more prevalent among Caucasians compared to Asians with neck flexor weakness (p&lt;1E-5) and muscle tenderness (p&lt;0.0001), being the most prominent. Most skin manifestations in adult DM patients were more prevalent among Caucasians, where photodistributed violaceous erythema was most pronounced (p&lt;0.0001). Fewer ethnic differences for JDM cases were found and none remained statistically significant after correction for multiple testing. As expected, the ADM patients displayed virtually no muscle manifestations and no significant differences were found. Comparison between prevalence of skin manifestations for Caucasian and Asian ADM patients showed a higher prevalence for most skin variables in Caucasians, with the difference in prevalence of periungual erythema being most striking (p&lt;0.00001). No significant difference in autoantibody profile between the two groups was found. Gender analyses for serology, muscle variables and skin manifestations revealed fewer differences compared to ethnic differences, and none remained statistically significant after correction for multiple testing. <h3>Conclusions</h3> We found significant ethnic differences in clinical phenotypes for DM patients. Comparable analyses showed no significant gender differences. Results from this study are of importance for the continued work in defining diagnostic and classification criteria as well as defining inclusion criteria in clinical trials. <h3>Disclosure of Interest</h3> A. Tjärnlund: None Declared, L. Rider: None Declared, F. Miller: None Declared, V. P. Werth: None Declared, I. E. Lundberg Shareholder of: Pfizer, Grant/Research support from: BMS