Concussions and traumatic brain injuries (TBI) have been considered a potential cause of ALS, also known as Lou Gehrig’s disease.

But a new study argues the association might be the other way around, with concussions providing an early warning sign among folks already in the early stages of ALS (amyotrophic lateral sclerosis).

The loss of muscle control that comes with early ALS might increase people’s risk for a concussion-causing fall or accident, researchers write in JAMA Network Open.

If that’s so, then “TBI in some individuals perhaps (reflects) a consequence of early, subclinical ALS,” concluded the research team led by Dr. William Stewart, a neuropathologist at Queen Elizabeth University Hospital in Glasgow, U.K.

For the study, researchers compared around 85,700 patients who’d had a traumatic brain injury with more than 257,000 matched people with no history of TBI.

During nearly six years of follow up, 150 cases of ALS occurred among all the study’s participants.

Traumatic brain injures were associated with a more than doubled risk of ALS, results showed.

However, that higher risk only lasts for two years following the concussion, researchers found.

In addition, there was no difference in age at diagnosis or death for ALS patients who’d sustained a concussion, compared to those who hadn’t.

“In this context, it seems plausible that the high ALS risk we observe in the years immediately following TBI might represent reverse causality,” researchers wrote.

“In other words, rather than TBI precipitating a neurodegenerative process culminating in ALS, TBI might represent an early complication of disease in individuals with preclinical ALS at risk of falls or other events culminating in TBI,” the team added.

A New York doctor who reviewed the findings said they indicate that doctors need to pay close attention to signs of degenerative brain disease among people who suffer a traumatic brain injury.

Doctors need to “follow them through their recovery from this injury and identify neurologically how they're doing,” Dr. Rosanna Sabini, medical director of the concussion program at Northwell Health, said in a news release. “The earlier you intervene, the more likely you have a chance to improve outcomes and life expectancy depending on the trajectory course.”

Sabini noted that ALS is a neurological disorder that happens as someone ages, attacking various particular parts of the brain and spinal cord. A motor neuron disease, it can affect any muscle in the body, she added.

“When you have that, potentially, you have progressive weakness of your muscles where you may not start be able to walk as well,” Sabini said. “Unfortunately, due to this aggressive loss of weakness, loss of strength, you end up having also difficulty breathing, and many will require a ventilator."