Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
Syringomyelia (cystic enlargement of the central spinal cord) is a chronic progressive disorder of the spinal cord. It usually presents with painless weakness and wasting of muscles of the hands and arms and also with segmental sensory loss. The sensory loss is usually of the pain and temperature variants sparing sensation of joint position and vibration. The symptoms are classically described as being in a "cape like distribution". If the syrinx enlarges, the posterior spinal cord may be involved which will then cause changes with joint position and vibration in the feet.
The questions include 1) where is the syrinx and 2) what caused the syrinx. Many of these are incidentally found. However, some may occur as a result of trauma, CSF (fluid surrounding brain and spinal cord) obstruction (an example would be a Chiari malformation as the previously post suggests), etc.
The blood work, I am assuming, is to check your kidney function to make sure it is safe to provide the gadolinium with the MRI.
I would suggest you continue following up with your physician to determine if the syrinx is a cause of your symptoms or just an incidental finding.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
You might want to post this in the chiari forum. That page gets more activity. I am not sure what the bloodwork would show but a syrinx may be caused from trauma or another condition ... like chiari. You will find more info on syrinx in chiari pages and find others with them as well.