A 9 year old male child presented with history of spiking fevers from last 2 months, which have been as high as 104degF. On examination, he has spindle-shaped swelling of multiple finger joints and complains of upper sternal pain. When he had fever, his mother noticed salmon-colored rash that resolves with the resolution of the fever. He had no conjunctivitis or any oral ulcers, but his hea sounds are muffled and he has pulsus paradoxus. Which of the following is the most likely diagnosis?

Juvenile idiopathic ahritis (Still's disease) It causes spindle-shaped swelling of finger joints and can involve joints such as the sternoclavicular joint. Presentation of JIA occurs as either polyahritis (five or more joints, systemic symptoms not so severe or persistent), oligoaicular (four or fewer joints, lower-extremity joints, extra-aicular disease unusual), or systemic disease (severe constitutional disease, systemic symptoms prior to ahritis, rheumatoid rash, high spiking fevers, variable joint involvement). The clinical features should be present for at least 6 weeks to make a diagnosis of JIA. This disorder can be associated with spiking high fevers and diffuse rash, which are not a feature of rheumatic fever, toxic synovitis, or osteoahritis.