They are completely different. TM is large area of demyelination, usually in the thoracic spine. It generally shows up on an MRI and can be diagnosed. Sometimes this is the first MS episode for some people. A person could be paralyzed from the area of the lesion down. People can recover completely or partially from this with no or serious disability. It is a problem in the spinal cord which means central nervous system.
Guillian Barre is a problem in the peripheral nervous system. It usually occurs after an infection of some sort, like viral. There is paralysis starting from the feet and going up. People usually recover from this.
Both of these can cause rapid paralysis but they are completely different.
In Guillain Barre syndrome radiculopathy is the most common phenomenon but other forms of myelopathy can also be.