Occurrence of focal myositis during Behçet's disease: The identification of a specific vasculitis-associated focal myopathy.

Abstract

This study aimed to report the association of focal myositis (FM) and Behçet's disease (BD) and to analyse the main characteristics of such an association. This is a retrospective multicentre study of patients with BD and FM (BD + FM+ group) and those without FM (BD - FM+ group). Clinical, laboratory, radiological, pathological, treatment and outcome data were analysed. The BD + FM+ group included 10 patients; the median [interquartile range] age at BD diagnosis was 25 [16-35] years, and at FM diagnosis, it was 30 [26-42] years. The diagnosis of BD preceded FM in the majority of cases (n = 8/10). FM occurrence was associated with BD flare-ups in three cases. The creatine kinase levels remained normal or slightly increased. Histological analyses identified relatively preserved muscle tissue, associated with vasculitis (n = 5/6). All patients required treatment; most patients relapsed (n = 9/10). The BD - FM+ group included 35 patients. A comparison of the groups identified a trend towards a younger median age at diagnosis of FM among those with BD (p = 0.063) and more frequent focal muscle swelling in the BD + FM+ group (p = 0.029). The pathological analysis identified significantly less frequent muscle alterations in the BD + FM+ group (muscle fibre size heterogeneity, p = 0.021; necrosis, p = 0.007; and fibrosis, p = 0.027). BD + FM+ patients had a higher frequency of relapse (p = 0.003) and systematic treatment (p = 0.042). FM occurring during BD appears to be part of the systemic vasculitis process and presents as a vasculitis-associated focal myopathy with a specific clinico-histological pattern. Patients with this association require long-term follow-up and adapted management. This case series also highlights the need for research on BD diagnostic criteria in cases of FM.