The patient was a 5-year-old Japanese female, with no known relevant family history, showed gradually progressive abnormal gait disturbance, regression of motor development, Raynaud’s phenomenon, and the shiny appearance of the skin of the face and extremities at the age of 2. The skin abnormality became more obvious, and a skin biopsy was performed from the left dorsal pedis at a previous institution when she was 5 years old. It revealed a fibrous thickening of the dermis, relative entrapment of an eccrine sweat glands, and thickened collagenous fiber. Based on the findings, she was referred to our hospital. She presented characteristic appearance with mask-like or mouse-facies as taut facial skin, loss of wrinkles and skin folds, puffy fingers with Raynaud’s phenomenon, and skin thickening of distal extremities beyond the elbows and knees (18/51 of the modified Rodnan total skin thickness score: mRSS) []. Grossly visible capillary hemorrhage on nail fold and severe abnormal capillaroscopy findings including bleeding, giant loop and disappearance of capillary consistent with the late phase in SSc. Contractures in the ankle and proximal interphalangeal joints resulted in gait disturbance and finger motion difficulty, respectively. There were neither abnormal neurological findings nor evidence suggesting myositis from information such as clinical muscle weakness, muscle derived enzyme, and muscle Magnetic Resonance Imaging at baseline intensive examination. Chest high-resolution computed tomography (HRCT) demonstrated patchy areas of ill-defined air-space opacity and consolidation predominantly involving the posterior basilar aspects of the lower lobes presenting with interstitial lung disease, although she had no symptoms suggesting respiratory abnormality, and no obvious finding could be detected by plain chest radiography. Serum KL-6 level was 197 U/mL and was within the normal range. No abnormal findings were detected by electrocardiography or echocardiography. She manifested neither heartburn nor dysphagia, and findings of gastroesophageal reflux disease were not identified by esophagogastroduodenoscopy. Esophageal dilatation and/or dysmotility was not indicated by the upper gastrointestinal series. Blood examination showed positive ANA (nucleolar and homogeneous nuclear staining at a serum dilution of 1:160 by indirect immunofluorescence). The commercially available SSc-related autoantibodies, including anti-topoisomerase I (Scl-70), anticentromere, and anti-U1RNP, were not detected. We then conducted an RNA immunoprecipitation assay and immunoprecipitation-immunoblot assay as previously described [, ]. The patient’s serum immunoprecipitated ribosomal RNAs and a 7 − 2 RNA that was consistent with the RNA component precipitated by a reference anti-Th/To-positive serum. In addition, the immunoprecipitation-immunoblot assay probed with anti-hPOP1 and anti-PM-Scl-100 antibodies revealed that the patient’s serum contained both anti-Th/To and anti-PM-Scl antibodies. The patient was diagnosed with diffuse cutaneous SSc, based on the Pediatric Rheumatology European Society/American College of Rheumatology/European League Against Rheumatism Provisional Classification Criteria for Juvenile Systemic Sclerosis []. She was treated with 2 courses of methylprednisolone pulse therapy (30 mg/kg/day for 3 days each course) followed by 10 mg/day of oral prednisolone (PSL). Subsequently, 6 courses of monthly intravenous cyclophosphamide (IVCY, 500 mg/m2 each course) therapy were administered. In the second course of IVCY, her skin thickening improved and the mRSS was 4/51. Just before the third course of IVCY, the interstitial lesions at the basal lung field were not identifiable on follow-up HRCT, and joint contracture also improved. After completing 6 courses of IVCY without major adverse events, she was maintained with 25 mg/day of azathioprine and PSL. Her PSL dose was reduced from 10 mg/day to 3 mg/day during 7 months of the time course.