Spinal cord involvement is usually central, uniform, and symmetric in comparison to multiple sclerosis which typically affects the cord in a patchy way and the lesions are usually peripheral. The lesions in acute TM are mostly limited to the spinal cord with no involvement of other structures in the central nervous system. Longitudinally extensive transverse myelitis A proposed special clinical presentation is the "longitudinally extensive transverse myelitis" (LETM), which is defined as a TM with a spinal cord lesion that extends over three or more vertebral segments. The causes of LETM are also heterogeneous and the presence of MOG auto-antibodies has been proposed as a diagnostic biomarker. Diagnosis Diagnostic criteria In 2002, the Transverse Myelitis Consortium Working Group proposed the following diagnostic criteria for idiopathic acute transverse myelitis: Investigations Individuals who develop TM are typically transferred to a neurologist who can urgently investigate the patient in a hospital. If breathing is affected, particularly in upper spinal cord lesions, methods of artificial ventilation must be on hand before and during the transfer procedure. The patient should also be catheterized to test for and, if necessary, drain an over-distended bladder. A lumbar puncture can be performed after the MRI or at the time of CT myelography. Corticosteroids are often given in high doses when symptoms begin with the hope that the degree of inflammation and swelling of the spinal cord will be lessened, but whether this is truly effective is still debated. Differential diagnosis The differential diagnosis of acute TM includes demyelinating disorders, such as multiple sclerosis and neuromyelitis optica, infections, such as herpes zoster and herpes simplex virus, and other types of inflammatory disorders, such as systemic lupus erythematosus and neurosarcoidosis. It is important to also rule out an acute cause of compression on the spinal cord. Treatment If treated early, some people experience complete or near complete recovery. Treatment options also vary according to the underlying cause. One treatment option includes plasmapheresis. Recovery from TM is variable between individuals and also depends on the underlying cause. Some patients begin to recover between weeks 2 and 12 following onset and may continue to improve for up to two years. Other patients may never show signs of recovery. Prognosis The prognosis for TM depends on whether there is improvement in 3 to 6 months. Complete recovery is unlikely if no improvement occurs within this time. Incomplete recovery can still occur; however, aggressive