Transverse myelitis is an acute spinal cord inflammation involving both sides of the spinal cord. TM symptoms develop rapidly over several hours to several weeks. Approximately 45% of patients worsen maximally within 24 hours. Most patients achieve partial or complete recovery within 1 to 3 months, after which time significant recovery is unlikely. TM is generally a monophasic illness (one-time occurrence); however, a small percentage of patients may suffer a recurrence, especially if there is a predisposing underlying illness.
Transverse myelitis is uncommon but not rare, affecting both adults and children. Conservative estimates of incidence per year vary from 1 to 5 per million population.