The exact reason for transverse myelitis is not known. Sometimes there is no known cause.

Viral, bacterial and fungal infections affecting the spinal cord may cause transverse myelitis. In most cases, the inflammatory disorder appears after recovery from the infection.

Viruses associated with transverse myelitis are:

Herpes viruses, including the one that causes shingles and chickenpox (zoster) Cytomegalovirus Epstein-Barr HIV Enteroviruses such as poliovirus and coxsackievirus West Nile Echovirus Zika Influenza Hepatitis B Mumps, measles and rubella Other viruses may trigger an autoimmune reaction without directly infecting the spinal cord.

Bacterial infections that are associated with transverse myelitis include:

Lyme disease Syphilis Tuberculosis Actinomyces Pertussis Tetanus Diphtheria Bacterial skin infections, gastroenteritis and certain types of bacterial pneumonia also may cause transverse myelitis.

Rarely, parasites and fungal infections may infect the spinal cord.

There are a number of inflammatory conditions that appear to cause the disorder:

Multiple sclerosis is a disorder in which the immune system destroys myelin surrounding nerves in your spinal cord and brain. Transverse myelitis can be the first sign of multiple sclerosis or represent a relapse. Transverse myelitis as a sign of multiple sclerosis usually causes symptoms on only one side of your body. Neuromyelitis optica (Devic's disease) is a condition that causes inflammation and myelin loss around the spinal cord and the nerve in your eye that transmits information to your brain. Transverse myelitis associated with neuromyelitis optica usually affects both sides of your body.

In addition to transverse myelitis, you may experience symptoms of damage to myelin of the optic nerve, including pain in the eye with movement and temporary vision loss. This can happen with or separately from transverse myelitis symptoms. However, some people with neuromyelitis optica don't experience eye-related problems and might have only recurrent episodes of transverse myelitis.

Autoimmune disorders probably contribute to transverse myelitis in some people. These disorders include lupus, which can affect multiple body systems, and Sjogren's syndrome, which causes severe dryness of the mouth and eyes.

Transverse myelitis associated with an autoimmune disorder may be a warning sign of neuromyelitis optica. Neuromyelitis optica occurs more frequently in people with other autoimmune diseases.

Vaccinations for infectious diseases have occasionally been associated as a possible trigger. However, at this time the association is not strong enough to warrant limiting any vaccine. Sarcoidosis is a condition that leads to inflammation in many areas of the body, including the spinal cord and optic nerve. It may mimic neuromyelitis optica, but typically sarcoidosis symptoms develop more slowly. The cause of sarcoidosis isn't understood.

This is all from Mayo Clinic.