Magnetic resonance images of myalgia with different etiologies in a patient with systemic lupus erythematosus

A Japanese female in her thirties with Sjögren's syndrome (SS) showed myalgia in her lower legs and extremities.One year and 5 months after classification of SS, systemic lupus erythematosus (SLE) [1] was classified based on anti-nuclear antibody with homogeneous and speckled pattern (1:320), bicytopenia, hypocomplementemia, elevated anti-double-stranded (ds) DNA, and anti-Sm antibodies.Elevated lactate dehydrogenase (LDH) (579 U/L, normal 124~322 U/L), creatine phosphokinase (CK) (513 U/L, normal 41~153 U/L), aldolase (16.9 U/L, normal 2.1~6.1 U/L), and C-reactive protein with myalgia that lasted for 3 months were observed.A manual muscle test of the biceps brachii and quadriceps femoris decreased to 4+/5, indicating muscle weakness.A positive electromyogram and muscle biopsy with high intensity on magnetic resonance imaging (MRI) [2] in her thighs and lower legs indicated myositis (Figure 1A and 1B) in SLE or SS, although myositis-related autoantibodies including anti-aminoacyl tRNA synthetase antibody; anti-melanoma differentiation-associated gene 5 antibody; anti-transcriptional intermediary factor 1-γ antibody; anti-Mi-2 antibody; antimitochondrial M2 antibody that were measured by enzyme immunoassay methods were negative.Pathologically, inflammatory cell infiltration around muscle fibers was observed in