Oct 112012
 

We all know that concussions are caused by hits to the head, but what actually IS a concussion and why is one forcing Dale Earnhardt, Jr. to step out of the car and effectively take himself out of the running for a championship?

How Do You Know You’ve Got One?

A concussion is a type of traumatic brain injury (TBI).  The Centers for Disease Control estimate that 1.7 million people suffer a traumatic brain injury every year.  A concussion is a mild type of TBI, but it is not (as we used to think) negligible.  Symptoms of concussion generally fall into four categories:  problems thinking and/or remembering and concentrating; physical signs like headaches, nausea, or balance problems; emotional distress like irritability, sadness or nervousness, and sleep changes.  Symptoms don’t always appear right away after a concussion – it may take days to notice them.  The concept of ‘concussion’ isn’t really well agreed upon by the experts. Most limit concussion to a state in which there is no physical brain damage.  There is even disagreement as to whether you have to lose consciousness to have an official concussion.

Dale Jr.’s doctor mentioned that he had a ‘special’ MRI (magnetic resonance imaging) scan.  I suspect it was a functional MRI scan – you can read more about that and its utility in sports here.

What is a Concussion?

If you were to open up a head, the first thing you would notice is the cerebrospinal fluid.  Your brain is not rigidly held in place in your head.  The cerebrospinal fluid surrounds your brain and gives it a cushion so that it doesn’t bang against the skull when you move your head suddenly.  It’s sort of like an internal helmet for your brain.  In a concussion, the motion of the head is so sharp that the cerebrospinal fluid isn’t able to provide adequate cushioning.  Interestingly, some researchers believe that it’s the rotation of the brain and not the straight-line  motion that is responsible for the damage.  In fact – Dale, Jr. noted during his press conference this morning that the Talladega crash was “only” 20 g, but he also said that he was spinning at Talladega.  Once the damage happens, it can persist for days to weeks — or longer.  We’re still figuring that out.

What we know is that a concussion changes the biochemical functioning of the cells in the brain.  A brain relies on two types of cells:  glial cells (which are like the brain’s pit crew, providing structural and metabolic support) and neurons.  The neurons (shown at right) are responsible for transmitting information.  The axon sends out information and the soma and dendrites receive information.  The information starts as an electrical pulse and then is converted into a chemical signal at the junctions between neurons.  In order for this to work, everything has to function correctly:  encoding the signal by the axon, the chemical processes that move the signal from neuron to neuron, and the decoding process by the soma and dendrites.  If any of these is impaired, the message is compromised.  You can think of a concussion as being like a cell phone in an area of poor reception.  Your cell phone, the person to whom your talking’s cell phone, and the transmission towers all have to work.  If they don’t, some things get through, but other things are jumbled and you can’t understand the message.

Your brain is one giant chemistry set.  When the electrical signals in your brain aren’t converted to chemicals appropriately, you end up with an imbalance of chemicals within the brain.  This means that your brain slows down – the cells slow down the process of dividing and become less active.  There can be a reduction in blood flow to the brain, and less energy is sent to the cells than they expect.  It’s very much like what happens when you get a cold – everything slows down in your body so that the immune system can focus on fighting off the cold.  In this case, however, it’s your brain that slows down.

The primary treatment for a concussion is rest – physical and mental.  A concussion impacts the functioning of the brain, so someone suffering a concussion needs to go easy on the thinking and external stimulus, as well as physically rest. The most important factor, thought, is that the brain is much more susceptible to long-term damage while it is recuperating.  If Dale Earnhardt, Jr. were in another crash this week, he could suffer more damage and it could be more severe.  We know that repeated concussions, like those sustained by football players or boxers, have the potential to cause long-term debilitating neurological diseases like Parkinsons or Alzheimers.  That’s why it is important for him to step out of the car this week.  I can’t imagine it was an easy decision for him to make; however, it was the right decision for him to make.

Questions

Q:  Why wasn’t Dale Earnhardt, Jr. diagnosed until now?

A:  Symptoms sometimes don’t show up for days — or weeks.  Also, many symptoms are possible to have without having a concussion – it’s the combination of symptoms that makes it a concussion.

As Dale, Jr. mentioned in his press conference, he didn’t tell anyone he had symptoms.  A more serious concussion could produce noticeable dizziness, lack of balance and coordination, vomiting or other symptoms, but the list of symptoms includes things like persistent headaches that aren’t apparent to doctors unless the patient says something.

Q:  Why sitting out two weeks?

A:  We don’t know how long it takes for the brain to heal.  It’s still healing, even after the immediate symptoms disappear.  Given the increased danger of possibly permanent damage if he were in another crash, this seems like a good decision.  Having two concussions within a few weeks of each other makes the situation worse.

Q:  If Dale, Jr. feels better in time for Kansas, could he race?

A:  Probably not.  Even when the symptoms lessen, there is still the increased risk for injury.  The patient feeling better is not a reliable indication that he is able to race.  Since they announced two weeks already, I’d be surprised if he’s at Kansas.

Q:  What is the “impact” test?

A:  ImPACT stands for Immediate Post-Concussion Assessment and Cognitive Testing.  It is a computerized test that takes about 20 minutes to complete and provides doctors with a way of assessing if there has been damage to the brain.    It’s a neurocognitive test – meaning that it tests how your brain is working.  Things like X-Rays and standard MRIs look at the physical condition of the brain – this looks at the functionality.  The test measures verbal and visual memory, how long it takes you to process information, and reaction time.  It consists of things like a series of three letters that you are asked to remember and reproduce, matching colors and shapes, etc.

Here’s the catch:  everyone is going to score differently on a test like this.  You can’t compare Dale Jr. and another driver and tell anything about Dale Jr.’s concussion.  If you don’t have a baseline measurement – a measurement prior to any concussions – you don’t have a way to tell whether there was brain damage or whether the subject just happens to have a slow reaction time.   You can re-administer the test after the brain has had time to heal and look for improvement, but you can’t compare it to the pre-concussion condition without a baseline measurement.  Seems to me that every driver ought to have a routine test done at the start of every season.  You can read more about ImPACT at their website.  They do caution that their test is ONE component in making a diagnosis and determining treatment.  NOTE:  read Dustin Long’s story on baselines and their importance.

 

 

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