A child, 10 years old, complaints of headache, an increase in body temperature 10 36.8 "C. hemorrhagic rashes on the shins, thighs, buttocks, swelling of the knee and ankle joints. soreness when moving. It is known from the history of the disease that 3 weeks ago he was ill with ARVI, his mother gave paracetamol to reduce the temperature. Against the background of taking medications, a fine-spotted rash appeared on the skin of the shins, swelling of the knee joints, soreness in them when moving. A pediatrician called from the polyclinic regarded the symptoms as an allergic reaction to drug therapy. The patient was advised to stop taking anti-inflammatory drugs. Antihistamines are prescribed. After 2-3 days, the rashes and swelling of the joints disappeared, arthralgia stopped. In dynamics, the condition worsened again: hemorrhagic rashes appeared on the lower extremities, thighs, buttocks, swelling and soreness in the knee and ankle joints when moving. headache and weakness increased. Objectively: the patient's condition is moderate, the body temperature is 36,8 °C. The skin is pale, dry. On the skin of the extensor surfaces of the feet, shins, thighs, hemorrhagic rashes, sometimes having a drain character. The knee and ankle joints are enlarged in volume, movements in them are painful. Acute cramping pain in the abdomen every 5-7 minutes, during which the patient rushes and moans. In the lungs, respiration is vesicular, BH-20 per minute. The boundaries of the heart are within the normal range, the tones are muted, tachycardia is 100 per minute, the rhythm is correct, blood pressure is 100/60 mm Hg. Data from laboratory research methods. Clinical blood test: Hb-90 g/l, leukocytes-12.6 x109/1, rod-shaped 12%, 3.23. ESR-34 mm/h, platelets-180x109/1. Clinical analysis of urine: relative density-1015, protein-0.33 mg/l, red blood cells-0-1 in the field of vision.