Spontaneous Headshake after a Kinematic Event (SHAAKE): Evaluating the Utility of a Potential New Sign in the Diagnosis of Concussion

<b>Background/Objectives</b>: 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. <b>Methods</b>: 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. <b>Results</b>: 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. <b>Conclusions</b>: 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.