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Título

IMMUNE-MEDIATED ANTI-SRP NECROTIZING MYOPATHY - A CASE REPORT

RESUMO

Clinical case: A 51 years old female started 6 months ago with muscle weakness in the upper and lower limbs and difficulty to raise the arms. She had dysphagia, alopecia, paresthesias in hands, and lost weight in the last 3 months. Physical examination showed proximal muscle strength grade of 3 in upper and lower limbs. The laboratory tests revealed abnormal high levels of CK (4.309), LDH (948) and aldolase (13). ANA test, anti-JO1, anti-SSA, anti-SSB, anti-SM and anti-RNP were negative. The autoantibody recognizing the SRP was positive. The electromyography showed myopathic pattern and the MRI of the thighs presented signs of myopathy with mild edema of the semitendinosus, hamstring, biceps femoris, tensor muscles of the fascia lata, diffuse muscle hypotrophy. Mild peripheral uptake by contrast medium and mild edema. The muscle biopsy revealed necrotic fibers, sometimes surrounded by myophagocytes. A significant variation in the size of muscle fibers was also seen, with several regenerated fibers and capillaries with mural thickening. Necrotic fibers and a few lymphocytes dispersed throughout the endomysium, in addition to the scarce sarcolemmal expression of MHC-I. She was treated initially with prednisone 60mg/day, but after a bad response to the glucocorticoid she received immunoglobulin human (IGIV) monthly during one year and rituximab each 6 months. Discussion: This report aims to expose a rare case of inflamatory myopathy, characterized by typical laboratory and clinical features including rapidly progressive muscle weakness, elevated muscle enzymes and characteristic histopathology of muscle biopsies. The immune-mediated necrotizing myopathy (IMNM) represents 20 to 30% of cases of inflammatory myopathy and is distinguished from other subtypes by the existence of necrosis of muscle fibers and absence of inflammatory infiltrate. Final Comments: IMNM, a type of autoimmune myopathy that has three different serologically subtypes: Anti-SRP, anti-HMGCR and antibody-negative IMNM myopathy. In histology these diseases have similar characteristics: myofiber necrosis in muscle biopsy, but the different subtypes have different risk factors, cancer risks, extramuscular manifestations and prognosis. These differences indicate that those are three different diseases, such as distinct pathological mechanisms and may respond to a variety of therapeutics modalities. More data on disease pathogenesis and optimal treatment of each subtype of IMNM are needed.