by Boston University School of Medicine

Credit: CC0 Public Domain

Concussion researchers have recognized a new concussion sign that could identify up to 33% of undiagnosed concussions. After a hit to the head, individuals sometimes quickly shake their head back and forth. Although it has been depicted in movies, television, and even cartoons for decades, this motion has never been studied, named, and does not appear on any medical or sports organization's list of potential concussion signs.

A new study, led by Concussion Legacy Foundation (CLF) CEO and co-founder Chris Nowinski, Ph.D., says it should.

The study, published in Diagnostics, reveals that when athletes exhibit this movement, which Nowinski and senior author Dan Daneshvar, MD, Ph.D., Chief of Brain Injury Rehabilitation in the Department of Physical Medicine and Rehabilitation at Spaulding Rehabilitation and Harvard Medical School, have named a "Spontaneous Headshake After a Kinematic Event" or SHAAKE, athletes report they had a concussion 72% of the time.

Among football players, the relationship was even stronger, with 92% of SHAAKEs associated with a concussion. A SHAAKE is usually initiated within seconds or minutes of an impact, involves lateral rotation side to side at a rate of two to eight movements per second, typically lasts less than two seconds, and does not occur for another reason such as a form of communication.

Nowinski recognized SHAAKE as a concussion sign after Miami Dolphins quarterback Tua Tagovailoa's controversial undiagnosed concussion during a game on September 25, 2022.

After Tagovailoa's head hit the ground, he rapidly shook his head side to side two separate times, before stumbling and collapsing. At the time, doctors attributed the collapse to a prior back injury, so he was not diagnosed with a concussion.

Had Tagovailoa been diagnosed with a concussion, he likely would not have been playing in a game the following Thursday, where he lost consciousness after experiencing a suspected second concussion in four days and was removed from the field on a stretcher.

Had SHAAKE been considered a sign of concussion, it would have provided doctors with additional evidence that his imbalance after the initial injury on September 25 was caused by ataxia due to concussion.

"Sports and medical organizations should immediately add SHAAKE to their lists of potential concussion signs," Nowinski said. "Coaches, medical professionals, and concussion spotters should be trained to recognize when a SHAAKE happens and remove athletes for further assessment. It's an easy change, with no downside, that could prevent catastrophic outcomes and save careers."

For the study, 347 current and former athletes between the ages of 18 and 29 were surveyed. They were shown video examples of SHAAKEs and asked about their experiences with them. 69% reported exhibiting a SHAAKE, and 93% of those reported a SHAAKE in association with concussion at least once. Athletes reported exhibiting SHAAKEs a median of five times in their lives.

"In the athletes we studied, about three out of every four SHAAKEs happened because of a concussion," said Daneshvar, who also serves as Co-Chair of Sports Concussion at Mass General Brigham.

"Based on our data, SHAAKE is a reliable signal that a concussion may have occurred, like an athlete clutching their head after contact, being slow to get up, or losing their balance. Just like after these other concussion signs, if athletes exhibit a SHAAKE, they should be removed from play and evaluated for a potential concussion."

The three most common reasons athletes reported for exhibiting a SHAAKE were "disorientation or confusion" (25%), "a feeling like you needed to jumpstart your brain" (23%), and "changes to your perception of space or perception of your body in space" (14%).

Other reasons athletes reported for exhibiting a SHAAKE associated with a concussion included headache, dizziness, inability to keep their train of thought, and changes to vision, hearing, or balance. Reasons athletes exhibited a SHAAKE that are not associated with concussion include neck pain, chills, pain that was not a headache, and an emotional reaction to the preceding event.

"Studies consistently show that an unacceptably high number of their concussions are not voluntarily reported by athletes, either because they don't realize they have a concussion or because, in the heat of the moment, they don't want to be removed from the game," said Robert Cantu, MD, CLF medical director and study co-author. "It is critical we take every potential concussion sign seriously to ensure the health and well-being of athletes."

The main limitation of the study is the potential for recall bias due to survey participants self-reporting prior concussions. Most respondents were from the United States and Canada, and it is unclear if SHAAKE varies by country or culture. Future prospective studies are needed to validate these findings.

More information: Christopher J. Nowinski et al, Spontaneous Headshake after a Kinematic Event (SHAAKE): Evaluating the Utility of a Potential New Sign in the Diagnosis of Concussion, Diagnostics (2024). DOI: 10.3390/diagnostics14202314

Provided by Boston University School of Medicine