Hi
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If it is the same shoulder as the arm through which dye or an intravenous injection was given, then in all probability it could be inflammation of the vein. This can cause excruciating pain at the site of inflammation which may correspond to the site of injection or a distance from it.
The pain can also be due to some shoulder injury, pinched nerve or any other cause like deep vein thrombosis.
Since it started just after MRA, please inform your doctor regarding it.
Take care!
You should immediately head for the ER where the MRA was taken. In every facility where dye contrast is administered I have never ever heard of a patient leaving without being told to return immediately if they felt any neurological symptoms or discomfort. The contrast medium used in the MRA generally is well tolerated, so I would not say that the connection is a certainty. The "missing piece" is the reason for the MRA. An MRI with dye dontrast to visualize blood vessels is called an MRA.