The Neurological Exam: Evaluating the Master OrganWritten by Gary Cordingley
How does a mind contemplate itself? That's a philosophical question I'll leave to minds smarter than mine, but what I can tell you is how to examine brain and other parts of nervous system.Most people are familiar with how doctors examine a heart or set of lungs. The physical exam of these organs consists mainly of using a stethoscope to listen to them in action. But when it comes to examining components of nervous system—consisting of brain, spinal cord, peripheral nerves and muscles—a stethoscope is pretty useless. The nervous system doesn't make sounds that doctor can listen to (though arteries in neck that deliver blood to brain can be usefully listened to). But because people can have medical disorders that damage nervous system, it is every bit as important to have a method for evaluating this organ as for any other. The method is called neurological exam. Because different parts of nervous system do different things, basic idea of neurological exam is to put patient through a number of mini-exams, each evaluating function of a different component. And what a variety of functions there are! In fact, apart from exposure to an inspiring teacher, this is what drew me into study of neurology in first place—the sheer diversity of neurological exam. This is an organ responsible for jobs as diverse as thinking, remembering, smelling, tasting, seeing, hearing, speaking, moving, walking, balancing, feeling and, yes, even contemplating itself—though I confess that my neurological exam doesn't include an assessment of self-contemplation. Moreover, nervous system handles many infrastructure tasks like controlling body-temperature, pulse, blood-pressure, breathing and enabling a person to urinate at a time and place of their choosing. What's not to admire about an organ system that can do so many things! The many mini-tests of neurological exam are bundled together in following sub-groupings: mental status exam, cranial nerve exam, motor exam, sensory exam and evaluation of stance and walking. I'll provide a brief overview of each. The mental status exam focuses on cerebrum which has a wrinkly, gray, outer surface usually shown in pictures of brain. The cerebrum is divided into eight lobes which includes pairs of frontal lobes, parietal lobes, temporal lobes and—bringing up rear—the occipital lobes. Each handles different mental tasks. In fact, even within a lobe, many different jobs are handled. So usual mental status exam consists of observing patient's behavior in exam room and using a variety of standard tests to check patient's orientation to time and place, attention, memory, speech, comprehension of language, memory, calculation and ability to track relative positions of objects in space. The next grouping of mini-tests, cranial nerve exam, also assesses functioning of parts of cerebrum, but additionally focuses on brainstem. The brainstem is located at base of brain and connects cerebrum above to spinal cord below. The cranial nerve exam includes tests of smelling, vision, constriction of pupils, eye-movement, facial sensation, facial movement, hearing, and action of certain muscles in throat, tongue, neck and shoulders.
| | Medical Tests: What Does a "Normal Range" Mean?Written by Gary Cordingley
We have a marvelous array of medical tests available to us. Many of them—typically blood-tests—even come with results expressed in numbers signifying exact quantity of something that was measured. On laboratory reports these measured quantities are often accompanied by a "normal range" for what laboratory apparently thinks value should have been, showing a lower number and a higher number. So if you had a laboratory test, what does it mean when your measurement falls inside or outside this range?It all depends on particulars. First of all, it matters what is being measured and why it was measured in first place. In theory, a laboratory test is ordered when doctor poses a question for which laboratory test is supposed to provide an answer. (If there was no question, how could lab-test be an answer?) For example, suppose a doctor is wondering if your hand tremors are due to too much thyroid-hormone in your bloodstream. So doctor's question is: Does this person have too much thyroid-hormone in bloodstream? A test measuring thyroid-hormone would provide a clean answer if it was either too high (yes) or within normal range (no). Because thyroid-hormone levels that are too low do not produce tremors, a measurement that was too low would be irrelevant to question posed. It might still warrant consideration in its own right as an "incidental finding," but is no different than a within-range outcome in answering original question. How about same blood-test, but with a different question? Suppose doctor is trying to figure out why you gained weight. The doctor knows that some people gain weight when their thyroid glands produce too little thyroid-hormone. So doctor's question is: Does this person have too little thyroid-hormone in bloodstream? This time, measuring thyroid-hormone would provide a clean answer to question if it was lower than normal range (yes) or within normal range (no). Because elevated thyroid-hormone levels do not usually cause weight-gain, a number higher than normal range would produce an answer to original question no different than one that was within-range. (But even if this outcome was unexpected, it might still be followed up.) For some blood-tests only meaningful result is in one direction. For example, a blood urea nitrogen (BUN) measurement assesses kidney function. If BUN measurement is too high, it could signify that kidney is impaired. But what does it mean if your BUN measurement is lower than normal range? It means absolutely nothing. It's a non-event. So then it's curious that a normal range for BUN even includes a lower number. How did it get there? These examples lead up to question of how normal ranges are created in first place. They are produced by statistics generated by measurements obtained in healthy volunteers. In case of BUN measurement, for example, this substance might get measured in blood of, say, 100 people without kidney disease. An average number would be calculated by adding numbers produced by all 100 people, and then dividing by 100. This average would be center of normal range. But upper and lower numbers are produced by another method looking at how widely spread apart BUN measurements are in these 100 people. After all, it would be highly unlikely that all 100 people would produce exact same number-value. So how far from average is still okay? The 100 measurements are plugged into a mathematical formula to compute a "standard deviation," a widely-used statistic related to how widely numbers are spread apart. Numbers that are farther apart produce a larger standard deviation, while numbers that are closer together produce a smaller standard deviation.
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