LAUSR

A 9-year-old Chinese boy was admitted to the Department of Paediatrics, Dongfang Hospital for painful swollen joints, rash and proteinuria. He had no fever, sore throat, cough, abdominal pain, melena, hair loss, light allergy, etc. His medical history of nasal and oral mucosal ulcers was remarkable. His family medical history was unremarkable. Physical examination revealed palpable purpura on buttocks and both lower limbs, no facial erythema, normal nasal and oral mucosae, no rales in both lungs, no pleural frictional sounds, normal heart rate, no arrhythmia, no pathological murmur in each valve, no pericardial frictional sounds, soft abdomen, no abdominal tenderness, subcostal 2 cm of the liver, untouched spleen under the rib, negative shifting dullness test, normal bowel sounds, mild swelling of the knee joints of both lower limbs with normal skin temperature, free movement of the knee joint and normal cranial nerve examinations. Additional studies were carried out with the following test results. Blood routine revealed haemoglobin 127 g/L, white blood cell count 7.28 × 10/L, platelet count 255 × 10/L. Urine dipstick was positive for blood (2+) and protein (3+). Red blood cells in urinary sediment were 20–24 every high power field, and the dysmorphic urinary red blood cells rate was 76%. Urinary protein quantification was 2.32 g/24 h. Urinary alpha1-microglobulin was 8.96 mg/L, and urinary β2-microglobulin was 0.22 mg/L. Faecal occult blood was negative. Blood biochemistry revealed plasma creatinine 50 μmol/L, urea 6.3 mmol/L, albumin 37.6 g/L, cholesterol 5.09 mmol/L, alanine aminotransferase 32.3 U/L, aspartate aminotransferase 23.6 U/L, total bilirubin 5.8 μmol/L, conjugated bilirubin 0.3 μmol/L, lactate dehydrogenase 231.0 U/L and creatine phosphokinase 37.0 U/L. Endogenous creatinine clearance was 3.63 ml/1.73m/s. Serum complement levels were normal with C3 1.09 g/L (range 0.9–1.8) and low with C4 < 0.075 g/L (range 0.1–0.4). Anti-nuclear antibody and anti-double-stranded DNA antibody titre was positive. AntiSmith antibody, anti-cardiolipin antibody, p-anti-neutrophil cytoplasmic antibody and c-anti-neutrophil cytoplasmic antibody titre was negative. Antistreptolysin O antibody level was 129.0 IU/ml. Anti-mycoplasma pneumoniae antibody titre was negative. The serum hepatitis B virus viral load was 1. 6 × 10 DNA copies/mL, and hepatitis B surface antigen (HBsAg), hepatitis B e-antigen and hepatitis B core antibody were positive, and hepatitis B surface antibody and hepatitis B e antibody were negative, but other viral markers including hepatitis C virus, human immunodeficiency virus, EpsteinBarr virus and cytomegalovirus were negative. D-dimer was 0.51 mg/L. The results of chest x-ray, electrocardiogram, heart, and kidney ultrasound examinations were unremarkable. Abdominal CTshowed hepatosplenomegaly. A diagnostic percutaneous renal biopsy was performed under the same local anaesthetic (Fig. 1) (Table 1). Chengdong Kang and Juan Huang contributed equally to this work.