Over 2.3 million people around the world have multiple sclerosis, yet there is no cure for the chronic, debilitating disease. In fact, the disease is still a huge mystery to scientists, and its cause is still questionable too. Though it may take some time for them to determine the cause, scientists can scratch one possible cause off their list. A new study has found that an abnormality in blood drainage from the brain, known as chronic cerebrospinal venous insufficiency (CCSVI), is not associated with multiple sclerosis (MS).

CCSVI has been a suspected cause of MS since 2009, when Dr. Paolo Samboni, from the University of Ferrar in Italy, first suggested that abnormalities in the way blood is drained from the brain and spinal cord may cause damage to the nervous system characterized by MS. Zamboni’s theory was based on venous narrowing, which could potentially cause iron in the blood to back up in the brain, The New York Times reports. In turn, nerves would get damaged, and MS would develop. During his study, he supposedly found that 100 percent of the MS patients had CCSVI, and subsequently developed a procedure to restore normal blood flow.

Ever since, Zamboni’s theory has been considered controversial, with scientists trying to prove and disprove it worldwide. One study from October found, through venous imaging technology and ultrasounds, that venous narrowing is actually pretty prevalent in the general population, and that it doesn’t prove causality for MS. Meanwhile, another study found that a treatment for CCSVI, called a liberation procedure, in which the veins are widened, did nothing to relieve symptoms of MS.

The current study also used a form of venous imaging called gadolinium-enhanced magnetic resonance venography, along with extracranial Doppler ultrasound, to compare blood flow out of the brain between 120 MS patients and 60 healthy controls. Both patients had one or more “proposed ultrasound criteria for diagnosis of CCSVI” in order to blind the testing radiologists to the patients’ actual clinical status. The researchers found that there were no differences between the two groups when it came to CCSVI.

“We detected no link between chronic cerebrospinal venous insufficiency and multiple sclerosis,” said Dr. Fiona Costello, of the department of Clinical Neurosciences and Surgery at the University of Calgary in Alberta, Canada, in a press release.

Costello and her team also questioned whether CCSVI diagnoses were really doing a service to patients. “We also identified several methodological concerns that challenge the validity of criteria used to define chronic cerebrospinal venous insufficiency, and in turn, we dispute the authenticity of this diagnosis,” she said. As the October study found, with CCSVI’s prevalence in the general population, people may be getting diagnosed for no reason. If that’s the case, then speaking with a health care provider may be a patient’s best bet.

Source: Costello F, Modi J, Lautner D, et al. Validity of the diagnostic criteria for chronic cerebrospinal venous insufficiency and association with multiple sclerosis. CMAJ. 2014.