Reeson for the unexplained bruise and slight swelling that appeared on the upper mid chest ?

See details: It is impossible to know without being able to examine the area. However, sternomanubrial joint inflammation can occasionally be seen in ra. That could explain it. Speak with your rheumatologist.

?injury: If the area is tender to touch, i would suspect a contusion. If nontender then a spontaneous burst capillary. Certain medications like aspirin, aleve, (naproxen) steroids promote fragile capillaries. Other causes include blood deficiencies(low platelets) or clotting problems from liver disease, etc.