Buffalo physicians announced Wednesday that they have started a large study that could overturn thinking about the generally accepted cause for multiple sclerosis.

MS is believed to stem from an abnormal response of the body’s immune system directed against the fatty sheath that surrounds nerve fibers in the brain and spinal cord.

But no one knows for sure, and recent research suggests an altogether different explanation for the disabling disease — narrowing of the primary veins outside the skull, a condition called chronic cerebrospinal venous insufficiency, or CCSVI.

The narrowing restricts the normal outflow of blood from the brain, causing alterations in the blood flow patterns within the brain that eventually cause injury to brain tissue and degeneration of neurons, the researchers said.

“If we can prove our hypothesis — that cerebrospinal venous insufficiency is the underlying cause of MS — it is going to change the face of how we understand MS,” said Dr. Robert Zivadinov, director of the Buffalo Neuroimaging Analysis Center at Kaleida Health’s Buffalo General Hospital.

Zivadinov, principal investigator in the study, is also a University at Buffalo associate professor of neurology.

Such a finding may allow doctors to identify individuals born with the abnormalities before they develop MS symptoms, treat the problem and perhaps even prevent it.

About 400,000 Americans suffer from MS, and because no cure exists, there is intense interest in new insights and potential treatments. Zivadinov urged caution, saying the work remains very preliminary.

A 2009 study by an Italian researcher, Dr. Paolo Zamboni, of 65 people with MS and 235 people with no or other neurological disorders found a strong relationship between MS and signs of abnormal blood drainage in veins. Zivadinov took part in small follow-up studies.

The researchers here now plan a larger, more rigorously designed trial that will involve 1,600 adults and 100 children and include a look at other factors involved in the disease.

It could be that CCSVI interacts with environmental, genetic or infectious triggers to initiate an abnormal immune response and the degeneration of nerve tissue, Zivadinov said.

The National Multiple Sclerosis Society, in a recent statement, offered a cautious response to the new study, saying that many questions remain about how and when the obstruction of veins might play a role in damage to the nervous system seen in MS.

“At the present time,” the organization said, “there is insufficient evidence to suggest that this phenomenon is the cause of MS.”