Overlap syndrome in a 12-year-old girl with systemic lupus erythematosus and anti-oj antibody-positive polymyositis: a case report

BACKGROUND: The peculiar presentation of overlap syndrome in children makes precise diagnosis difficult. Children with overlap syndrome may or may not have specific antibodies. We present the case of a 12-year-old girl diagnosed with overlap syndrome of systemic lupus erythematosus (SLE) and juvenile polymyositis (JPM) who tested positive for anti-OJ antibodies. CASE PRESENTATION: We describe the case of a 12-year-old girl diagnosed with SLE at the age of 7 and presented with fever with malar rash, periungual erythema, generalized weakness, and multiple joint pain at admission. The patient had persistent joint pain and weakness after intravenous methylprednisolone administration and complained of an inability to walk with a positive test for Gower's sign one week after admission, accompanied by elevated alanine aminotransferase (ALT) and creatine-phospho-kinase (CPK) levels. The results of nerve conduction velocity test were normal. Electromyography revealed abundant spontaneous activity and myopathic motor unit action potentials in the right deltoid, biceps, and iliopsoas, in addition to fibrillation and mild myopathic motor unit action potentials in the right rectus femoris muscle. Magnetic resonance imaging revealed diffusely increased signal intensities in the myofascial planes of the bilateral iliopsoas, gluteus, obturator, pectineus, and hamstring muscles. Anti-nuclear antibody, anti-RNP, and rheumatoid factor IgG tests were positive, and inflammatory myopathy autoantibodies revealed anti-OJ antibody positivity, which strongly indicated autoimmune myositis. High-resolution computed tomography of the lung revealed mild pericardial effusion without any evidence of interstitial lung disease. We initiated intravenous pulses of methylprednisolone treatment, followed by cyclosporine, mycophenolate mofetil, and oral steroids. Clinical improvement with a delayed, slowly reduced CPK level after the above treatment and she was discharged after the 18th day of hospitalization. CONCLUSION: Overlap syndrome with inflammatory myositis can occur years later in pediatric SLE cases. We should be alert when patients with SLE develop a new presentation characterized by decreased SLE-specific autoantibody titers, positive anti-RNP antibodies, and elevated CPK. Treatment of the overlap syndrome of SLE and JPM is individualized, and the course differs between pediatric and adult patients.