The FDA has issued an alert warning about risks, including death, associated with endovascular treatments for multiple sclerosis based on the controversial theory that the disease is caused or exacerbated by blocked cerebrospinal veins.

Called chronic cerebrospinal vascular insufficiency (CCSVI), the theory has polarized the MS community since an Italian researcher proposed it in 2009. Many patients and some physicians immediately embraced it, but most mainstream neurologists have been deeply skeptical.

Read the full release from the FDA.