This article is ideally going to serve as part 1 in a 3-part crash-course on concussion – no pun intended. Concussion, also interchangeably called mild traumatic brain injury (mTBI), is becoming a sort of “popular” injury.
In 2011, the generational NHL star Sidney Crosby began his long road of concussion recovery, bringing attention to the injury. In the 2015 movie Concussion, Will Smith played Dr. Bennet Omalu, the physician credited with discovering chronic traumatic encephalopathy (CTE) in American football players on autopsy. Just a week ago, on January 17, 2021, NFL quarterback Patrick Mahomes was hit and overtly showing 3 (of 6) sideline signs of concussion and was enrolled in the NFL concussion protocol in the following days.
Of those three examples, Sidney Crosby’s story is probably closest to the middle path that the research shows at this point. The evidence is far from clearcut on CTE, and on the flip side, it’s not medically prudent for Mahomes to “clear” a concussion protocol in just seven days. Ideally, this 3-part series puts to rest some overhyped and misconstrued fears and instills the confidence to sit out and seek help when it’s needed.
What is a concussion (mild traumatic brain injury)?
A concussion is a functional and transient (temporary) form of traumatic brain injury (TBI) that occurs when sufficient force is transmitted to the brain either directly or indirectly.
Let’s clear up four misconceptions right here:
- You can’t have a “mild concussion” or a “severe concussion.” There is only “concussion (mTBI).” You sustain one, or you don’t. There is no grading system for concussion severity.
- Your brain does not bruise in a concussion. Part of the diagnostic criteria in concussion (mTBI) is that there are no imaging findings on CT/MRI. A bruise to the brain (i.e., contusion) would appear on imaging and likely result from a more significant TBI. The “coup-contrecoup” injury is an outdated model of concussion.
- You do not have to “blackout” to have sustained a concussion. It turns out that less than 10% of all concussions involve a loss of consciousness. Said differently, more than 90% of concussion cases maintain consciousness and do not blackout.
- You do not have to be hit in the head to sustain a concussion. A concussion is an acceleration-deceleration injury that causes functional damage to your brain. Think about car accidents or military blast injuries. The force makes its way to the brain via “whiplash-like” movement causing acceleration-deceleration in the skull.
So, why is it called “mild” TBI? The answer to this comes back to the grading of traumatic brain injuries. We have mild, moderate, and severe TBIs. For a quick and tangible perspective shift, consider that severe traumatic brain injuries (sTBI) are associated with mortality (i.e., death) in the first year after injury. In contrast, concussion (mTBI) is associated with prolonged symptoms in the first year after injury. Below is a breakdown of TBI grading based on consciousness, memory, and imaging.
What you’ll find is that in a concussion (mTBI), you may only have a single moment of feeling woozy, followed by concussion symptoms in the coming hours to days.
What are the symptoms of concussion (mild traumatic brain injury)?
Because your nervous system is the final common pathway to nearly everything that your body performs – from contracting muscles to secreting hormones to crafting dreams as you sleep – the brain is the “master controller.” Thus, when a traumatic force functionally disrupts your brain, nearly every part of your life will be affected.
A concussion comes with physical, mental, and emotional symptoms. The Post-Concussion Symptom Scale (PCSS) is a commonly used and validated means of tracking concussion symptoms and includes the following physical, cognitive, and psychological symptoms:
Many athletes, coaches, and parents don’t know that after an impact, if you have even a single one of these symptoms, a concussion should be considered. It does not mean that a single symptom is enough for a concussion diagnosis. That’s because concussion symptoms are non-specific. Research has found that 24-33% of “healthy, non-brain injured” patients meet the ICD-10 Post-Concussion Syndrome (PCS) criteria. This underscores the need for a concussion-literate physical exam when symptoms appear after an impact.
What happens to the brain in a concussion?
Let’s save the diagnosis and treatment for Part 2, but let’s assume that it’s happened – you sustained a mild traumatic brain injury.
Research has described a “neurometabolic cascade” that occurs in your brain when your nerve cells get stretched and sheared by the impact. To summarize some fancy biochemistry and physiology:
- Functional stretching and shearing of your neurons. The acceleration and deceleration cause your nerve cells (neurons) to stretch and twist. Not enough to tear, or we’d see it on imaging, but enough to open pores and protein channels that allow molecules to cross back and forth across the cell membrane.
- Excitotoxicity and inflammation. The molecules that rush into and out of your neurons are electrolytes (e.g., sodium, potassium, chloride, magnesium, and calcium). Calcium is excitatory and causes the release of glutamate. Glutamate is a signaling molecule (neurotransmitter) in the brain that causes more excitation. So, calcium excites cells to release glutamate, which further excites cells causing “excitotoxicity” and inflammation. When this is happening, you feel disoriented, stumbly, etc…
- Energy and blood flow deficit. Your neurons have to go into overdrive to “clean up” the electrolyte mess – that takes lots of energy (ATP). Simultaneously, calcium has flooded your neurons and “clogged” your mitochondria, dramatically slowing down ATP-production. In a cruel trick of nature, concussion also involves an autonomic component where blood flow to the brain is disrupted. So, your brain needs blood, oxygen, and nutrients to clean up the mess – but it is not getting proper blood flow.
How long does a concussion last?
We’re going to look at a textbook, “if everything goes right” concussion. We’ll talk about post-concussion syndrome (PCS) in part 2.
After impact, that energy deficit grows. The calcium imbalance lingers for approximately four days, blood flow dysregulation can last 7-10days or more, and all the while, your brain has to recover from that electrolyte party. This drains your brain’s energy to its lowest at around 3-5 days after injury, and that’s typically when you’ll feel your worst, as well.
Beginning around a week (7-10 days) after injury, your symptoms may start to go away. This is why you’ll see so many athletes cleared on a Sunday-to-Sunday schedule. There’s a problem with this thinking, though, because symptom recovery does not equate to metabolic recovery.
Your brain energy levels likely don’t return to baseline normal until approximately 22-30 days after injury. Suppose an athlete sustains a second concussion too close to the first one. In that case, there’s a risk for a fatal or career-ending injury (e.g., Second Impact Syndrome), or at the very least a significantly delayed recovery (e.g., months vs. weeks).
Quick recap
A concussion is a functional and transient TBI secondary to direct or indirect head trauma. Physical, mental, and emotional symptoms tend to peak 3-5 days after injury and go away in 7-10 days. Symptom recovery does not equal metabolic recovery, as it takes approximately 3-4 weeks for brain energy levels to return to normal.
In part 2, we’ll look deeper at what a diagnostic workup looks like and the evidence-based treatment options.
