Below is an instruction that describes a task. Write a response that appropriately completes the request. ### Instruction: 15 y/o male, R arm swellingHello doctors of Reddit,My brother is a 15 yo male with 1 week of R arm swelling and mild/dull pain on shoulder abduction . He is an avid basketball player who trains very hard and he uses his right arm to shoot the ball. 3 days prior to onset of swelling someone hit him hard on the right shoulder. He didnt think much of it, but has mild ecchymosis on the shoulder.1 day after symptom onset he went to the ER. Ultrasound negative for DVT and echogenic material. CT scan of arm and chest negative for blood clots and mass. CT scan did not see a cervical rib but noted minor thoracic inlet narrowing. CBC normal PT/INR normal CPK elevated D dimer positive (ER physicians were unconcerned due to imaging) Protein C/S normal factor Leiden V normal Normal radial pulseHe was sent home with hematology and vascular surgeon follow up. The ER physicians suspect this is an overuse injury causing some type of impingement that resulted in the swelling of the arm.So far his arm circumference has dropped by 1 inch and his arm feels less tight, as in you can pinch the fat, which was difficult to do before. His pain has improved. We will follow up with the specialists but also a sports medicine doctor.Could this really be an overuse injury? Can such an injury really cause the whole arm to swell?Thank you all.. ### Response: Holy shit at that ER work up. Seems.. thorough.Could be the bruise or a muscle strain causing swelling as well.