The Neuro Exam: What the heck is this doctor thinking?

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Doctors today have a lot of new imaging tools like MRIs and PET scans that they can use to “see” inside of your brain and identify many problems, but a careful examination of the patient to assess which systems are and are not working properly is still the primary tool that neurologists rely on to decide where they need to look and how to get the kinds of pictures which will give them an answer.  The first step in diagnosing a neurological condition therefore usually begins with an assessment of neurological functioning called the Neuro Exam.   If your problem is serious enough to send you to an emergency room, you may get a very short version of this exam before your treatment begins, with a more detailed assessment being performed later.  So, a Neuro Exam might last only 2 minutes in the Emergency Room or it might take 40 minutes in your doctor’s office.  It may involve primarily having your doctor stare at you, looking at your pupil sizes, facial muscles, body posture, swallowing, and spontaneous muscle movements, or you may be performing calisthenics and answering a hundred rapid fire questions.  It all depends on how obvious your symptoms are to your doctor’s trained eye and how serious your condition appears to be.   

The details of each Neuro Exam will vary depending on what symptoms you show up with, and your doctors training.   There are many different styles of testing that different doctors prefer to use, but there are several common elements.  In general, your doctor will be trying to answer four basic questions: (1) Is this really a nervous system problem, or is it some other problem which just happens to be affecting your nervous system?  (2) What is the most likely cause of your symptoms?  Are they likely due to toxins, an infection, an autoimmune or allergic reaction, an injury, blood flow disruption, a genetic disease, or some unknown cause?  (3) Is the central nervous system being affected, the peripheral nervous system, or both?  (4) What is the most likely location of the problem?   

Most medical exams, including Neuro Exams, will usually start by taking your temperature and blood pressure, and probably also drawing a sample of your blood for analysis.  Your brain has a relatively narrow range of tolerance for temperature, glucose, and oxygen levels.   So, if your blood pressure or blood sugar are low, or if you have a high fever, it may cause you to act abnormally.   A diabetic going into insulin shock can look a lot like someone who is drunk or suffering from a stroke.  Someone with a spiking fever may look like they are having an epileptic seizure.   If the problems with your nervous system are being caused by something outside of your nervous system, it will be important to treat the root cause quickly in order to avoid permanent nervous system damage.   

Narrowing down the range of possible causes is the next priority, and this determination can be a critical.   If your doctor believes that you are suffering from an autoimmune condition, but you are actually suffering from a viral or bacterial infection, then the immunosuppressants that he/she prescribes can allow the infection to spread more rapidly.  If your doctor believes that you are suffering from an infection, but you have really been exposed to a toxin, then the antiviral drugs or antibiotics could cause your liver or kidneys to fail.  If your doctor thinks that you have had a stroke from a blood clot, but you actually have a ruptured aneurism or bleeding inside of your skull from a head trauma, then the clot busting drugs (anticoagulants) will only cause even more bleeding.  It is also possible that you could have two distinct problems.  You could have a brain infection and be a heavy drinker with liver function problems.  This would require a different kind of treatment than if you had only one problem

If your condition is sudden and serious, your doctor will want to begin treating your condition as quickly as possible.  Brain cells can die very quickly, and I do not know about you, but I do not have a lot of extra brain cells to spare.  However, your doctor will also want to get the treatment right, or at least not get it horribly wrong.  This is why it is so very important that you answer all questions as truthfully as possible.  Many people are reluctant to tell their doctor the truth about their sexual histories or drug use, fearing that their doctor will be less motivated to treat them well if they disapprove of their lifestyles.  However, in this case, inaccurate information could get you killed.   If there is any possibility that you are HIV positive, have an undiagnosed STD, or took a contaminated street drug, then your doctor needs to know that before he or she gives you something that will make your condition much worse.   As a general rule, if your doctor asks you the same question three or more times, it means that if you are not telling him or her the truth, what they are about to do could kill you.  (Are you absolutely sure that you did not hit your head when you fell?   Is there any possibility that you might be HIV positive?  This is your last chance to come clean.)

The central nervous system (brain and spinal cord or CNS) and peripheral nervous system (nerves or PNS) are vulnerable to different types of diseases and chemical toxins.  Therefore, the first broad determination that your doctor will try and make is whether the problem is central or peripheral.  This is where the little rubber hammer tapping your knee or the pricking of your fingers comes into play.  If the speed or strength or these reliable peripheral reflexes is reduced, your doctor would begin thinking about a peripheral nervous system disease or some sort of systemic toxin which slows nerve conduction.  If these reflexes are OK, then your doctor will begin focusing on your central nervous system.

Your doctor faces two challenges in assessing the functioning of your central nervous system (CNS).  The first problem is that a system can fail due to faults anywhere in the system.   Knowing a single problem will not tell him/her very much.  Your doctor will need a lot of data points about what systems are and are not working properly in order to locate the problem.  The second problem is that your doctor cannot rely on what you tell him/her about your symptoms.

When your nervous system is not working properly, you become an extremely poor judge about how well it is working.  This is because the very instrument that you are using to analyze your brain’s functioning is itself out of order.  People have been known to go completely blind and yet swear that they could see just fine, making all sorts of excuses for why they kept bumping into the walls and furniture.  Since your visual cortex is the only part of your brain that really knows what vision is, the rest of your brain cannot tell when what your visual cortex is telling it about the world is only a guess.  Similarly, if your speech centers are affected, you could be speaking gibberish and not understand why no one comprehends your clear and lucid statements.  In the same way that you would have to rely on the expertise of an interpreter in a country where you did not speak the language, the rest of your brain must rely on the truthfulness and accuracy of the information that it receives from each of the other specialized regions of your brain.  If your brain is damaged, that trust can be misplaced.  Since your judgment may be impaired by your condition, it can be very useful to have a trusted friend or relative with you to help you make any treatment decisions.  Your doctor is likely to be a virtual stranger, so you are more likely to trust a friend when they tell you that you are not OK, and you really should spend the night in the hospital.   

Since your doctor can’t take your word for anything, he or she may have to ask you to do all sorts of crazy things that do not seem to have anything to do with the symptoms that brought you to the hospital, just so that he/she can find out if parts of your brain which you think are working just fine are, in fact, not working at all.   This can get annoying when your doctor is testing your pain sensitivity, short term memory, or reasoning skills.  Your doctor might even try and test your emotional responses by deliberately trying to make you angry.  So-called “flat affect”, or lack of emotional responsiveness, can be an important clinical cue.  Basically, your doctor is going over a wiring diagram of your nervous system, checking each individual circuit before going on to the next one.

After your Neuro Exam, you will typically be sent for some sort of imaging to confirm and/or refine the initial diagnosis.   In the early stages after an injury or at the onset of disease symptoms however, the results of these scans can be inconclusive.   This is why you are usually not just sent for an X-ray or MRI before seeing a neurologist and why you often have to go back for a second set of images a couple of days later.   An X-ray can only detect bleeding inside of your skull after enough iron has accumulated in one spot for the X-ray to see and it cannot detect the kinds of small bleeds that occur after a mild concussion.  An MRI cannot detect a stroke or Multiple Sclerosis attack until after a significant number of cells have died and begun to be cleared away and, even then, they cannot always show which of these diagnoses is correct.   In addition to the technological limitations of these scans, there is also the matter of cost and time.  Insurance companies will not pay for tests with a low probability of being useful and there may be several car accident victims ahead of you waiting for their scans.  Do you really want to have contrast agents injected into your blood stream and have to lie in an MRI machine for a couple of hours in order to scan your entire brain and spinal cord at the highest possible resolution, when your doctor is pretty sure that a ten-minute scan of your brain stem without contrast enhancement will give him/her all of the information that they need?  It is just not possible to run every kind of test and do every kind of scan which might possibly provide some useful information.  It is not financially responsible to do so, and it would take too long to get this information for your doctor to be able to use the information in time for you to benefit from the treatment.