Concussion researchers say they have recognised a new concussion sign that could identify up to 33% of undiagnosed concussions, particularly on the sports field, and which they believe needs further investigation.
After a blow to the head, individuals sometimes quickly shake their heads back and forth, a motion which has been frequently depicted in movies – and even cartoons – for decades, but which has never been studied or named.
Nor does it appear on any medical or sports organisation’s list of potential concussion signs.
A recent study, however, led by Concussion Legacy Foundation (CLF) CEO and co-founder Chris Nowinski, PhD, says it should.
The study, published in Diagnostics, reveals that when athletes exhibit this movement, 72% of the time they have a concussion.
Nowinski and senior author Dan Daneshvar, MD, PhD, Chief of Brain Injury Rehabilitation in the Department of Physical Medicine and Rehabilitation at Spaulding Rehabilitation and Harvard Medical School, have named the motion Spontaneous Headshake After a Kinematic Event, or SHAAKE.
Among football players, the relationship was even stronger, with 92% of SHAAKEs associated with a concussion, they found.
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 recognised SHAAKE as a concussion sign after an American rugby player’s controversial undiagnosed concussion during a game in September 2022. After the player’s head hit the ground, he rapidly shook his head from side to side twice 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 he been, however, he would probably not have been playing in a game the following Thursday, where he lost consciousness after experiencing a suspected second concussion in four days and had to be removed from the field in a stretcher.
If SHAAKE had been considered a sign of concussion, it would have provided doctors with additional evidence that his imbalance after the initial injury was caused by ataxia due to concussion.
“Sports and medical organisations should immediately add SHAAKE to their lists of potential concussion signs,” Nowinski said. “Coaches, medical professionals, and concussion spotters should be trained to recognise 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 aged 18 to 29 were surveyed. They were shown video examples of SHAAKEs and asked about their experiences with them.
A total of 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 realise 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.
Study details
Spontaneous Headshake after a Kinematic Event (SHAAKE): Evaluating the Utility of a Potential New Sign in the Diagnosis of Concussion
Christopher Nowinski, Samantha Bureau, Daniel Daneshvar et al.
Published in Diagnostics on 17 October 2024
Abstract
Background/Objectives
Diagnosing concussions is problematic, in part due to the invisible nature of concussion symptoms, in addition to personal and interpersonal factors that influence symptom reporting. As a result, observable signs of concussion can ensure concussions are identified and appropriately treated. Here, we define a potential novel sign, the spontaneous headshake after a kinematic event (SHAAKE) and evaluate its utility in the diagnosis of concussion.
Methods
A cross-sectional survey study of 347 athletes (age 27, IQR: 25–29; 47.6% female; highest level of play: college—46.1%, high school—41.2%) identified whether SHAAKE occurred, the reasons underlying SHAAKEs, and its utility for self-reported concussion. Sensitivity and positive predictive value were calculated across all sports and these parameters, as well as estimates for specificity and negative predictive value leveraging published helmet sensor data, were calculated for football players.
Results
The median number of times participants reported SHAAKE was 5 (IQR: 3–10), with 4 (IQR: 2–7) associated with a self-reported concussion. Overall, 84.9% of participants reported concussion symptoms as the most common reason for their SHAAKEs. Across all sports, SHAAKE had a sensitivity of 49.6% and positive predictive value 72.4% for diagnosing concussion. In football players, SHAAKE had a sensitivity of 52.3%, estimated specificity of 99.9%, positive predictive value of 91.9%, and estimated negative predictive value of 99.5% for diagnosing self-reported concussion.
Conclusions
These results demonstrate that nearly three-quarters of athletes reported a SHAAKE associated with a self-reported concussion, which supports the potential for SHAAKE to be used as a concussion screening tool.
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