Window 8: Motor Sensory Exam Of Brain Function

Written By: David Burns

motorA motor and sensory exam is a standard part of any neurological exam. At Brain Centers NW the difference is not what tests are being performed. The difference is that while the black and white standard which is good enough for a pathological / ablative diagnosis (e.g. root compression) it is not enough when considering general function and the existence of patterns that may reflect a bigger picture of brain / nervous system integrity.

Let’s start with strength. There is a standard grading system that is applied to muscle testing. This grading system is helpful when we are talking about pathology or ablative lesions. It is not as helpful when we are talking about strength as a reflection of a “physiological lesion”.

When looking at things from a functional standpoint a physician considers the general pattern and relative weakness of various muscles, as they are compared from left to right, upper vs lower extremity and front vs back (e.g. bicep vs tricep). If a muscle is relatively weak on its own, than that means something different than if it falls within a certain pattern. That is to say, if we are going to say that a muscle is weak as a consequence of the areas that “feed it” like brainstem (e.g. rubrospinal vs reticulospinal), cerebellum or brain, than there should be a pattern of weakness that relates to the supposed deficit, because these areas don’t just fire that one muscle.

Now this certainly is more subjective than other tests and the skill in this type of assessment varies, and is dependent on the physician own brain integrity, which is partly the reason why the findings are considered in concert with the other findings. That is, does what I’m finding make sense when considering the other findings? Lastly, if a lesion is physiological in nature than one would expect that the patterns of weakness would recover and recover faster than they might with an ablative lesion or “hard” lesion.

Reflexes like muscle strength testing are considered not in isolation but rather within the context of all the findings including each reflex tested. Like all the tests performed in a functional neurological exam, it is not just the strength of the response that is evaluated but how quick a response is and is it a sustained response. When you are looking at reflexes from a pathological standpoint you are looking at a diminished response for peripheral lesion (i.e. motor neuron and out to muscle) or an increased response with a central lesion (i.e. cord, brainstem, brain), that is upper vs lower motor neuron lesion.

From a functional standpoint you obviously including a pathological perspective but you are also considering patterns in a similar manner to what is done when looking at strength. This is why you may see me repeatedly check reflexes pre and post applications. I’m not simply looking for if there is or is not a reflex at this point but rather what is the quality of reflex and did it change post application.

Pathological reflexes are tests that look for a response that should not normally be present. That is, the reflex is one that may have been origionally normal to see as a baby (e.g. toes up going when stroke the bottom of foot) but is not normal once the system is matured. A mature system attenuates or inhibits these responses and when present in a mature system suggests that an area is weak. Some of the pathological reflexes are seen in both physiological “lesions” and pathological. If something suggesting a hard vs. soft lesion is noted it will be communicate to the patient. Pathological findings are investigated first and hard lesions ruled out prior to considering the softer physiological lesion.

Sensory findings, like all other findings, could be a reflection of where the information comes in (e.g. skin poked with pin), the track up through the spinal cord, the brainstem or the area of brain that integrates sensory input. Different sensations are tested because they take different paths up through the spinal cord to brain. A picture is built based off of what sensation is lost, where it is lost and how it compares to left vs right or upper body vs lower body.

When it comes to brain and sensory integration we will look at things like awareness of individual fingers with eyes closed, ability to perceive what letter is written on hand, being able to different what object is heavier. Sometimes, when doing a functional exam a sensory pathway may be used to note what difference it makes to another system or function (e.g. vibration on balance). Change noted would give us insight into the areas being challenged.

This blog and the other blog “windows” into brain function are not intended for anybody to make any diagnosis or determine treatment for anybody. It is simply intended to help patients understand what a functional approach to neurology, brain function, concussion management, sports performance evaluation may entail. But most importantly, to help the patient or client communicate with the provider so that they or their children can achieve the best brain health possible. Achieving optimal brain health is an interdependent process, an active process that starts with communication.

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