A Houston Methodist-led team of researchers have found COVID-19 can result in an unexpectedly frequent occurrence of acute transverse myelitis (ATM), a rare but often devastating spinal cord disorder.

The team's study of documented pandemic cases found that 43 involved ATM, an inflammation of the spinal cord that prevents sensory and motor information from flowing to the brain and the rest of the body. The cases occurred in both developed and underdeveloped countries.

"There were significantly more cases than what we would have expected," says Dr. Gustavo Roman, a Houston Methodist neurologist and the study's lead author. "In fact, the numbers make COVID-19 one of the most common causes of acute transverse myelitis."

Dr. Roman adds that the study confirms that the novel coronavirus targets the nervous system, both the brain and the spinal cord, second only behind the lungs. The virus was initially considered mostly a pulmonary disease, coming from the same family that gave the world the SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome) outbreaks.

First time COVID-19 has demonstrated a link to ATM

Previous COVID-19 cases have been linked to neurological conditions such as stroke, but the new study is the first to show an association between the virus and ATM.

The study, a collaboration between Houston Methodist and Panama researchers, was published online this spring in the journal Frontiers in Immunology. Dr. Roman is chairman of the Environmental Neurology Group of the World Federation of Neurology, the association that represents 122 neurological societies around the world.

ATM, which occurs when the immune system attacks healthy myelin covering the nerve bundles in the spinal cord, can cause weakness or paralysis of the legs and arms, loss of bladder and bowel control and significant pain. It develops as a result of trauma, tumors, stroke, infection or neurological disorders such as multiple sclerosis.

Normally, about one case occurs for every 1 million people per year.

That's why Dr. Roman believes the COVID-19-related cases merit additional investigation. After the paper's publication, two more cases were reported in Egypt, bringing the total known number of such ATM cases to 45.

A breakdown of the cases around the world

That's out of about 85 million COVID-19 cases counted globally as of January, when the study was completed. Dr. Roman says he didn't think there were additional unreported cases because ATM would not escape researchers' notice.

The study found patients had developed spinal cord lesions after contracting the virus in 21 countries. The highest incidence was in Iran, which has reported seven cases, followed by Italy and the U.S., both with six, and the United Kingdom with four.

The patients ranged from 3 to 73 years of age, and included 23 men and 20 women. Three were children.

The damage caused by the virus was severe, said Dr. Roman. Only a couple of patients recovered.

Nearly 60% of the patients suffered either total paralysis or muscle weakness of all four limbs. The rest had a loss of sensation and movement in the lower body.

What causes the ATM cases — the virus or the inflammatory response?

Dr. Roman says the cases included both those in which ATM quickly followed the COVID-19 infection and those (the majority) in which it developed some time after the virus was detected. A quick onset came in one-third of the cases, a longer onset in two-thirds.

Dr. Roman adds that the latter cases suggest the inflammatory response triggered by the patient's immune response to the virus was the primary cause of the condition. Early-onset cases suggest the damage was inflicted by the virus itself.

"This review confirms that ATM is not uncommon as a neurological complication associated with COVID-19 infection around the world, responsible perhaps for 1.2% of all neurological complications caused by this coronavirus," the paper concluded. "Research to identify the responsible antigens and immunopathogenesis of COVID-19-associated ATM must be encouraged."

Three additional cases analyzed by the team were found in research conducted on the AstraZeneca vaccine. It is unclear if those cases are directly linked to the vaccine.

Researchers from Hospital Paitilla, Interamerican University of Panama and Hospital Santo Tomas collaborated with Dr. Roman on the study.