Researchers are uncertain of the exact causes of transverse myelitis. The inflammation that causes such extensive damage to nerve fibers of the spinal cord may result from viral infections, abnormal immune reactions, or insufficient blood flow through the blood vessels located in the spinal cord. Transverse myelitis also may occur as a complication of syphilis, measles, Lyme disease, and some vaccinations, including those for chickenpox and rabies. Cases in which a cause cannot be identified are called idiopathic.
Transverse myelitis often develops following viral infections. Infectious agents suspected of causing transverse myelitis include varicella zoster (the virus that causes chickenpox and shingles), herpes simplex, cytomegalovirus, Epstein-Barr, influenza, echovirus, human immunodeficiency virus (HIV), hepatitis A, and rubella. Bacterial skin infections, middle-ear infections (otitis media), and Mycoplasma pneumoniae (bacterial pneumonia) have also been associated with the condition.
In post-infectious cases of transverse myelitis, immune system mechanisms, rather than active viral or bacterial infections, appear to play an important role in causing damage to spinal nerves. Although researchers have not yet identified the precise mechanisms of spinal cord injury in these cases, stimulation of the immune system in response to infection indicates that an autoimmune reaction may be responsible. In autoimmune diseases, the immune system, which normally protects the body from foreign organisms, mistakenly attacks the body’s own tissue, causing inflammation and, in some cases, damage to myelin within the spinal cord.
Because some affected individuals also have autoimmune diseases such as systemic lupus erythematosus, Sjogren’s syndrome, and sarcoidosis, some scientists suggest that transverse myelitis may also be an autoimmune disorder. In addition, some cancers may trigger an abnormal immune response that may lead to transverse myelitis.
An acute, rapidly progressing form of transverse myelitis sometimes signals the first attack of multiple sclerosis (MS), however, studies indicate that most people who develop transverse myelitis do not go on to develop MS. Patients with transverse myelitis should nonetheless be screened for MS because patients with this diagnosis will require different treatments.
Some cases of transverse myelitis result from spinal arteriovenous malformations (abnormalities that alter normal patterns of blood flow) or vascular diseases such as atherosclerosis that cause ischemia, a reduction in normal levels of oxygen in spinal cord tissues. Ischemia can result from bleeding (hemorrhage) within the spinal cord, blood vessel blockage or narrowing, or other less common factors. Blood vessels bring oxygen and nutrients to spinal cord tissues and remove metabolic waste products. When these vessels become narrowed or blocked, they cannot deliver sufficient amounts of oxygen-laden blood to spinal cord tissues. When a specific region of the spinal cord becomes starved of oxygen, or ischemic, nerve cells and fibers may begin to deteriorate relatively quickly. This damage may cause widespread inflammation, sometimes leading to transverse myelitis. Most people who develop the condition as a result of vascular disease are past the age of 50, have cardiac disease, or have recently undergone a chest or abdominal operation.