Can ALS be caused by traumatic brain injury?

Amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease) is a neurologic disease that damages nerve cells in the spinal cord and brain, causing widespread muscle wasting and weakness. It strikes without warning, usually beginning between the ages of 55 and 75. As it worsens, ALS disables a person’s ability to move, speak, eat, or breathe. Although two FDA-approved medications can modestly slow its progress, death generally occurs within three to five years of diagnosis.

Decades of research have failed to come up with a definite cause. However, one new study supports a link between playing professional football and ALS.

Why is ALS called Lou Gehrig’s disease?

Since it was first described in the 19th century, much about ALS has remained mysterious. It’s quite rare, affecting about two in 100,000 people. It might have remained a disease you’d never heard of if not for Lou Gehrig, the Hall-of-Fame baseball player who played for the New York Yankees in the 1920s and 1930s. He developed ALS at age 36 and died of the disease two years later. Since then, ALS has often been called Lou Gehrig’s disease.

In recent years, widespread social media campaigns, such as the Ice Bucket Challenge, have raised awareness and funding for ALS research.

Searching for a cause of ALS

Some research suggests that risk factors for ALS include:

• Genetics: Genes passed down through families contribute to about one in 10 cases
• Smoking: In one study, the heaviest smokers had a 26% higher risk of developing ALS compared with those who had never smoked
• Pesticide exposure, such as pesticides used on crops
• Unusual infections with certain bacteria or viruses
• Bodily injury severe enough to impair activities of daily living
• High levels of physical exertion, as is common for elite athletes or members of the military
• Head trauma, including concussions and repeated, less severe head injuries. While chronic traumatic encephalopathy (CTE) has been closely tied to head injuries, the role these injuries play in developing ALS is less certain.

New research links playing professional football with ALS

A new study published in JAMA Network Open might help us better understand the cause of at least some cases of ALS. It strongly suggests that playing professional football may be a risk factor for the disease.

• Between 1960 and 2019, 19,423 men played in the National Football League (NFL). During that time period, 38 were diagnosed with ALS and 28 died of the disease.
• Among these current and former football players, the risk of developing ALS and dying of the disease was nearly four times higher than that of men in the general population.
• NFL players who developed ALS had a longer average football career (seven years) than those without the disease (4.5 years).
• Many NFL players were in their mid-30s at the time of their ALS diagnosis. This is quite a bit younger than is typical for ALS.

Importantly, this study did not assess why there might be a relationship between ALS and playing professional football. The study authors speculate that traumatic brain injury might be to blame.

How certain are these findings?

This was an observational study. Observational research can identify a link between a possible risk factor (in this case, playing in the NFL) and a disease (ALS). However, it cannot prove that the risk factor caused the disease.

For studies like this, it’s always possible that a confounder — a factor not studied or accounted for — might explain the connection. For example, this study did not collect information about head injuries, pesticide exposure, smoking, or family history. This means it can’t provide insight into whether these factors played a role in ALS risk.

In addition, the study identified diagnoses of ALS among NFL players only through Google News reports and obituaries. The diagnoses weren’t confirmed by a review of the players’ medical records. Therefore, cases of ALS could have been missed or misdiagnosed.

It’s also possible that the study missed cases of ALS among less famous players whose health news or deaths might be overlooked by the media. To account for this, the researchers logged indicators of NFL fame (including selection to the NFL Pro Bowl and Hall of Fame). They found no difference in ALS risk among more famous and less famous players.

The bottom line

Public health experts and researchers are trying to sort out which sports harm brain health, and to recommend ways to protect against brain injuries. Expert recommendations for contact sports have evolved to include protective equipment, changes in game rules, limiting participation by younger players, and discouraging participation after a head injury until recovery is complete.

As noted, studies have strongly linked brain injury from concussions and repetitive head injuries. This latest study suggests some cases of ALS may also be caused by brain trauma.

Lou Gehrig reportedly had multiple concussions over the course of his sports career. Regardless of whether he actually had Lou Gehrig’s disease or CTE with features of ALS, this new research raises the possibility that his demise might have been due to traumatic brain injury. And that should serve as a reminder that even as we cheer on those with inspiring athletic talent and win-at-all-costs determination, protecting the health of sports participants should be even more important.