Second impact syndrome (SIS) is a devastating condition that occurs when an individual who suffers from initial concussive symptoms due to a head injury sustains a second impact upon their head before fully recovering from the first blow. The brain is in a vulnerable state in the aftermath of a concussion, and even a slight blow can cause a sudden chain of reactions in the body that leads to dangerous brain swelling. Given the severity of second impact syndrome, it should be actively discussed between doctors and patients during post-concussive care and considered as a variable in Return-To-Play protocol for concussed athletes. There have been very few cases of the condition, but the cases that have taken place are so severe that it’s necessary and worthwhile to take steps towards SIS prevention in all concussion care.
What is Second Impact Syndrome (SIS)?
Second impact syndrome was first described in 1973 by R.C. Schneider, after he witnessed two cases of athletes experiencing initial concussion syndromes and then dying after only minor second injuries. The term itself was later coined by Schneider in 1984. The condition is considered rare, but exact numbers are relatively unknown due to the frequent underdiagnosis of initial injuries and the similarities shared between SIS and other traumatic brain injuries. SIS can be hard to conclusively diagnose because it requires establishing a causal relationship between the initial and secondary head injuries. While missed diagnosis of SIS has made it difficult to know how many cases there are annually, a 2016 study published by researchers from Indiana University School of Medicine in Pediatric Neurology found that only 17 cases have been fully documented over the past few decades in medical literature.
Despite the rarity of second impact syndrome, it is increasingly important that both doctors and patients are aware of its possibility and take steps to prevent its onset, given its deadliness.
When a concussion occurs and its diagnosis is missed or symptoms are covered up or ignored, then there is the opportunity for SIS. “Even though the exact frequency of second impact syndrome is not well established because it is so hard to identify, diagnose and treat, it can be avoided if each and every suspected concussion is thoroughly evaluated using objective measures like VOMS, infrared eye tracking and neuro-cognitive testing,” says Dr. Schaller. “Since it is often fatal or can result in severe physical and mental impairments, missing any concussion and properly treating that concussion for safe return to play, can be met with a severe or even deadly outcome. Therefore, identifying and diagnosing all concussions is very important.”
Why is a Second Impact so Dangerous for People Recovering From a Concussion?
When an individual experiences a concussion, the body undergoes a number of neuronal, metabolic and ionic changes in response. One such change is seen in axonal shearing – the tearing of the brain’s long connecting nerve fibers as the brain rapidly shifts inside the skull when an injury occurs. Axonal shearing leads to a number of neural responses, dysregulating and decreasing cerebral blood flow to a point in which edema – swelling due to excess fluid – takes place. It takes time and energy for the brain’s neurotransmitters to return to their normal physiology after a concussion — generally, the return to normalcy is thought to take seven to 10 days, but it often takes longer in young people. Thus, during such a time period, the post-concussive brain is particularly vulnerable to further injury.
“Trying to cover up a concussive event by an athlete or even a parent can lead commonly to long term issues with balance, cognition, migraine headaches, visual tracking and anxiety and/or depression—which studies have found affect 37% of young athletes with concussions),” says Dr. Schaller. Returning to play before an athlete is fully recovered and then sustaining another concussion before the prior concussion is fully recovered not only raises the rare possibility of SIS, says Dr. Schaller, but it snowballs the effect of these same very issues of balance, cognition, migraine headaches, anxiety, depression and visual tracking.
SIS Presents Itself Rapidly and in Various Ways
“After the second impact, SIS may present itself in different ways,” says Dr. Schaller. “For example, a person may initially appear to be stunned, with dilated pupils, but still be conscious enough to continue moving. Then, within minutes, they can lose consciousness and collapse into a frightening semi-comatose state.”
This was seen in the case of Zackery Lystedt. Lystedt was a high school football player in the state of Washington in 2006 when he was injured during a game. He returned to the field after only a brief moment on the bench and subsequently suffered another blow. Within seconds of this additional blow, he collapsed to the ground, losing consciousness and suffering a hemorrhage in his brain. Lystedt was lucky to survive, but his survival came at a cost: part of his skull was removed to relieve pressure, he spent seven days on life support, and he’s since spent years relearning basic cognitive and motor skills. Lystedt’s case led to the signing of the Lystedt Law in Washington State in May 2009, considered one of the toughest Return-to-Play laws in the country. This law prohibits any athlete suspected of sustaining a concussion from returning to play without the explicit approval of a healthcare provider.
Physiopedia summarizes SIS as we might witness in athletes as a situation where the individual may actually be able to get up and stay on his or her feet long enough to walk off the field, but within a few minutes time (or less), they may collapse and show signs of respiratory failure — something that might be mistaken for a cardiovascular emergency. Other potential symptoms experienced during this initial moments after the second impact period include seizures, headaches and vomiting.
After being rushed to the hospital, SIS can be diagnosed with a computed tomography (CT) scan to see if the patient has cerebral swelling, midline brain herniation and acute subdural hematoma. If this occurs, the situation is life-threatening and neurosurgical team will removal of half of the skull, leaving just the scalp and relieving pressure in the brain to avoid herniation.
How Can Second Impact Syndrome Be Prevented?
According to National Center for Biotechnology Information (NCBI) resources, prevention should be the priority in addressing second impact syndrome because the condition is very difficult to treat upon onset. Education on the syndrome among both patients and medical professionals is one of the best ways to prevent SIS — because the syndrome is so rare, it is often left out of post-concussive care. The group most at risk for SIS is young males between the ages of 13 and 24 — particularly athletes in high contact sports such as American football, hockey and boxing.
Being aware of what the condition is prior to a first concussion is one of the best ways to prevent SIS, because it allows patients and their care teams to make informed decisions about how to protect themselves and their brain after an initial TBI. Time and rest are the best solutions. Concussed individuals should rest both cognitively and physically for an extended time period after their concussion.
“The key is not total rest, but modified rest,” says Dr. Schaller. “For example, they need to avoid noisy and crowded places, avoid reading and screen time, avoid travel over 30 minutes a day, avoid cardiovascular efforts like jogging and heavy weight lifting, avoid sweating and heat exposure, etc. But concussion patients are encouraged to walk, gather with a small group of friends and extend their cardiovascular and lifting exercises in a graduated supervised fashion with a trained medical professional.” He notes that after they graduate a five-stage vestibular rehabilitation program, patients can they safely return to sports. However, athletes should not be allowed to return to play if they continue to exhibit any concussion symptoms, which include:
- Fatigue
- Headache
- Disorientation
- Nausea
- Feeling “in a fog”
Return to Play After Initial Concussions Impacts SIS Risk
Even when these symptoms are no longer present, it is always better to err on the side of caution and not rush the return to play or work regardless of circumstance. Any athlete who has returned to play after a concussion should be watched carefully, even if they have had an appropriate recovery period and completed a return to play protocol. Doctors, athletic trainers, medical providers, patients and their family should work together to determine the best protocol for their individual case. When an athlete does return to play, they should be watched carefully.
“Remember, return-to-play protocols does not mean concussion recovery is one-size-fits-all,” says Dr. Schaller. “Every patient’s journey back to from a brain injury is going to be different, which is why they need to be monitored and follow their doctor’s orders.”
The Best Way to Avoid Second Impact Syndrome is Still to Prevent the First Impact
In the end, the ultimate way to prevent second impact syndrome is to prevent any concussions from happening in the first place. In high-risk activities such as impact sports or wheeled activities (such as cycling or skateboarding) you should #RockYourHelmet and wear a well-fitting helmet that is appropriate for the activity you’re partaking in. For sports such as football and rugby, practice safe and proper techniques for tackling and other forms of direct contact. When riding in a motor vehicle, it is important to always wear your seatbelt and utilize age- and size-appropriate car and booster seats for children.
Furthermore, if you sustain a head injury and suspect you might have a concussion, you should immediately take steps to rest and recover and prevent further concussions. Athletes should be removed from play after a suspected head injury, even when exhibiting only mild concussion symptoms, and they should not return to play until they have been evaluated by a medical professional. Taking preventative steps in both protecting your head and recognizing initial injury are the ultimate ways to continue enjoyment of activities and sports while also preventing second impact syndrome.
MAC Alliance and Second Impact Syndrome Prevention
Mid-Atlantic Concussion (MAC) Alliance is a network of certified medical professionals and athletic trainer affiliates located throughout Delaware, Maryland, New Jersey, New York, Pennsylvania and Virginia. We work with a wide array of traumatic brain injury cases, including post-SIS patients. It is our mission to raise SIS awareness and help reduce risks for the syndrome — starting with better diagnosis and care for initial concussions. We use a number of state-of-the-art brain monitoring tools for concussion diagnosis and treatment to mitigate the effects of brain trauma, including ImPACT, CBS Health, EyeGuide, RightEye and BrainScope assessment tools. We are committed to the welfare of our patients through the diagnosis, treatment and long-term care management of concussions and traumatic brain injuries. For more information, click here to find the nearest MAC Alliance partner to you or call us at (303) 235-8808.
—Reporting by Rebecca Rainey
[UPDATED: 8/30/23]
[ORIGINAL POST: 8/18/21]
