The results of nerve conduction velocity test were normal. myopathic motor unit action potentials in the right deltoid, biceps, and iliopsoas, in addition to fibrillation and slight myopathic motor unit action potentials in the right rectus femoris muscle mass. Magnetic resonance imaging exposed diffusely increased Bmp2 transmission intensities in the myofascial planes of the bilateral iliopsoas, gluteus, obturator, pectineus, and hamstring muscle tissue. Anti-nuclear antibody, anti-RNP, and rheumatoid element IgG tests were positive, and inflammatory myopathy autoantibodies exposed anti-OJ antibody positivity, which strongly indicated autoimmune myositis. High-resolution computed tomography of the lung exposed slight 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 having a delayed, slowly reduced CPK level after the above treatment and she was discharged after the 18th day time of hospitalization. == Summary == Overlap syndrome with inflammatory myositis can occur years later on in pediatric SLE instances. We should become alert when individuals with SLE develop a fresh 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 definitely individualized, and the program differs between pediatric and adult individuals. Keywords:Overlap Syndrome, Systemic Lupus Erythematosus, Polymyositis, Anti-OJ antibody == Background == Connective cells diseases (CTDs) are inflammatory conditions with characteristic signs and symptoms that define specific disorders. However, some children simultaneously manifest ATP (Adenosine-Triphosphate) signs and symptoms characteristic of two or more major rheumatic disorders, such as juvenile idiopathic arthritis, SLE, juvenile dermatomyositis, cutaneous systemic scleroderma, and vasculopathy. Children with these disorders are often hard to categorize according to the existing classification criteria and are referred to as overlap syndromes. Children with overlap syndrome may or may not have specific antibodies, and cannot ATP (Adenosine-Triphosphate) be assigned to a single disease entity. Sometimes, the demonstration is so peculiar that a exact analysis is definitely clinically very difficult, and specific treatment is not initially possible. Additionally, fatal outcomes may occur before a diagnosis. Here, we report a case of SLE diagnosed at the age of 7 years, with fever and skin rash as the initial presentation. Raynaud’s phenomenon and joint pain developed during four years of treatment. At the age ATP (Adenosine-Triphosphate) of 12 years, she presented with fever, malar rash, periungual erythema, multiple joint pain, ATP (Adenosine-Triphosphate) and muscle weakness, which eventually led to the diagnosis of overlap syndrome of SLE and JPM with positive anti-OJ antibodies. This case report was approved by the institutional review board of Changhua Christian ATP (Adenosine-Triphosphate) Hospital (IRB number 220113). == Case report == A 12-year-old lady was admitted to Changhua Christian Childrens Hospital in May 2021, complaining of intermittent low-grade fever for one week and SLE flare-up. This lady was diagnosed with SLE in 2017 and presented with low-grade fever, malar-distributed facial rash, oral ulcers, and enlarged lymph nodes. The examination revealed a hemoglobin level of 10.4 g/dL and a platelet count of 2.88 105mm3. Urinalysis revealed proteinuria but no hematuria. The liver function test showed an ALT level of 22 U/L; however, the renal function test results were normal. There were strong positive antinuclear antibodies (ANA) (1:1280 pattern), anti-dsDNA (684 IU/mL), positive anti-sm, positive anti-SSA, and anti-RNP(2.0 AI); C3 and C4 levels were 31.6 & below 6.7 (mg/dL, respectively). She was initially administered pulse corticosteroid therapy and then treated with mycophenolate mofetil, azathioprine, and hydroxychloroquine. During the four years of treatment, she had an uneven clinical course and persistently low complement levels. Two years after being diagnosed with SLE, Raynaud’s phenomenon affecting the fingers was observed, along with new-onset wrist and knee joint pain; therefore, she received additional methotrexate. One week before hospitalization, she developed fever and was treated with Baktar in the oral form (sulfamethoxazole 400 mg + trimethoprim 80 mg) for a suspected urinary tract infection. However, the fever persisted and was accompanied by an obvious malar rash, periungual erythema, generalized weakness, and multiple joint pains (wrist, knee, and fingers without swelling or limited range of motion). The patient was then admitted for further evaluation and treatment. Physical examination revealed ulcers around the bilateral buccal surfaces; rash on the face (malar distribution, presented with erythema over cheeks; nasal bridge but with spared nasolabial folds); enlarged right cervical lymph node with tenderness; right flank knocking pain; and localized heat on the right knee..