Q. 10-year-old child presented with a history of high-grade fever with convulsions with impaired liver function tests. His liver functions improved over the period of next two days. But his fever continued. After 5 days of improved liver functions, he developed arthritis of both ankles and wrist joints with a persistent high fever. His CBC shows anemia with thrombocytosis, with ESR of 110, with CRP strongly positive, with ANA, ANTI ds DNA negative, and RA factor negative. He's still running a fever and has arthritis in similar joints. What investigations should we do next? And what will be DD`s for him?