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Examination of Cortical Sensation

by Stephen Holt, MD, MS

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    00:00 Alright, so we've covered all of the motor stuff, it's time to move on to the next tier of sensory processing. We've talked before about assessing for vibration sense and proprioception, etc., the cortex needs to take all that information that's coming in and integrate it and make sense of it. And so, this next set of tests are designed to assess cortical sensation, so called cortical sensation as opposed to the peripheral vascular system with proprioception, etc. So what we're going to have our patient do is do 3 quick tests to make sure that specifically the parietal lobes are integrating all that information that's coming up from the spinal cord. First one we'll do is called stereognosia. Alright, so for stereognosia I'm going to basically have you close your eyes and put out your left hand.

    00:50 "And I just want you to try and identify what that is in your hand." "It's a house key?" "Perfect, that is a key. And now give me your right hand. And see if you can identify what that is." "A quarter?" "Perfect. Now you got exactly not that it's just a coin but actually that is a quarter, so that's perfect." So, the ability to take all the information and sensory information and process it is the work of the parietal lobe and that tells me that that is functioning well. And now they're great, that's called stereognosia, the next one is called graphesthesia. "Can I have your left hand again? And I'm going to draw a letter or a number and I want you to see if you can identify what it is." "Number 3." "Perfect. Your right hand." "Is that a plus sign?" "Perfect." So, that's graphesthesia. And the last one we'll do to assess for parietal lobe function is called extinction and what I'm simply doing is oftentimes if there are descent inputs to both hemispheres but one is deceased in some way you may be able to process sensory information if there are no distractions but if you sample both sides at the same time the dominant parietal lobe will detect a sensation whereas the other lobe may may not be able to detect it. "So, can you feel this?" "Eyes closed?" "Eyes closed, sorry." "Can you feel this on the left?" "Yes." "Can you feel this on the right?" "Yes." "Can you feel it on both sides?" "Yes." So, a patient who is having a subtle stroke or subtle problem with the parietal lobe or even the sensorimotor strip on either side may have extinction, that is sensory extinction. When you apply stimulus to both sides, they are no longer able to feel it on the affected side. With that, we can move on to higher cortical processing having just done cortical sensation. We're going to just touch on higher cortical functioning, executive functioning in so far as we're talking about tests for dementia and for delirium. Now for dementia, there is a variety of well-validated, widely disseminated instruments that you can find online in our all part of downloadable material such as the Folstein's Mini-Mental Status Exam, the Mini-Cog, the Montreal Cognitive Assessment, and even just the clock drawing test. I'm not going to go into these or demonstrate these because they are essentially a script that you walk through, anybody could walk through them, it's very straightforward.

    03:10 They're also available in almost every language on the planet and so I just invite you to familiarize yourself with those particular instruments because they are very useful validated tools to assess for early or advanced dementia and staging dementia over time. For delirium, there is also a variety of tools that are out there. It is a clinical bedside diagnosis and the tool that I often use is the confusion assessment method, the CAM. And it has only 4 components and the patient has to have 3 out of those 4 components to meet the criteria for delirium. The first 2 are required components. And that is the patient's mental status should be acutely changed and fluctuating. So this is not something where the person has had a slowly indolent progression of memory loss or what have you over the span of weeks or months. Delirium is, by its nature, a fluctuating mental status. Secondly, the patient should have problem with attention. So if I said to you "I want you to close your left eye and wiggle your right finger while tapping your left toe." That's a very complicated, coordinated task.

    04:16 He requires some degree of attention to be able to do that. A patient with delirium is not going to be able to attend to things in that way so you have to have both of those criteria, the fluctuating acute mental status change and a problem with attention and then either of the next 2 findings. So, one would be disorganized thinking and that's simply if I ask him to tell me why he is in the hospital or tell me some other piece of information if he's tangential, not making sense, can't follow his own line of thinking, that would be evidence of disorganized thinking. And then the last thing would be altered level of consciousness. So if the patient is having trouble staying awake if I have to do a sternal rub or what have you to wake him up again, either of those 2 things would be that 3rd criteria and it's necessary for the confusion assessment method. And that's the full assessment of delirium.


    About the Lecture

    The lecture Examination of Cortical Sensation by Stephen Holt, MD, MS is from the course Examination of the Cranial Nerves.


    Included Quiz Questions

    1. Fluctuating mental status
    2. Stereognosis
    3. Meningitis
    4. Tactile extinction
    5. Graphesthesia
    1. Ask the patient to identify an object in their hand with their eyes closed.
    2. Write a number on the patient’s hand and ask them to identify it.
    3. Ask the patient to outstretch their arms in front of them and then put one finger on their nose.
    4. Ask the patient to stand with both feet together and eyes closed.
    5. Apply a tactile stimulus to both hands and ask the patient which side they feel it on.

    Author of lecture Examination of Cortical Sensation

     Stephen Holt, MD, MS

    Stephen Holt, MD, MS


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