Diagnosis by letter :-(((( Still, at least you’re getting to see the neuro very soon.
The letter is saying that you have a lesion in your thoracic spinal cord, in line with the vertebrae T3/4-T5/6. These are in your upper back; the second and third vertebrae after the end of your neck. The lesion is mainly in the right half of the cord.
Hopefully the neuro will explain it all on Wednesday. Make sure and take a list of questions and try to take someone with you if you can - the extra ears and eyes can come in very handy (never mind having someone handy to give you a hug if you need it).