Thursday, October 28, 2010

Abnormal posturing made overly simple by request!

I forgot who asked for this, but it's a good topic for Auntie Jo's Occasional Ridiculously Oversimplified Take on Neuroscience. This time, we'll look at Abnormal Posturing and Why It's A Bad Thing.

There are a lot of different abnormal postures out there, "abnormal posture" being defined as "the way that your body is holding itself, involuntarily, that clues us in that something is not right with you." If you're sitting leaned over to one side at about 45 degrees, that's an abnormal posture. If you're standing, kind of hunched over, with your arms akimbo, that's an abnormal posture. Those aren't as bad, though, as two of the most basic postures, decorticate and decerebrate. We call them "responses" or "poses", by the way, because they show up in response to external stimuli.

Decorticate posturing, also called flexor response or mummy pose, means that you've got fairly substantial damage to a number of structures in the brain that normally keep you from getting stuck in a flexed position. (You want me to be more specific? Fine, but don't start complaining when I start using terms like rubrospinal tract and vestibulospinal extension tracts.) You're lying down with your arms bent and your hands in fists on your chest, like a mummy.

Decorticate posturing is a bad deal, because it usually means damage to the thalamus (without which you really can't get along), the midbrain, and the cerebral hemispheres, which is where all your thinking, speaking, and remembering goes on. Essentially, you could "recover" from the sorts of injuries that would lead you to show decorticate posturing, but you'd not do much more going forward than stare and twitch.

Decerebrate posturing is also called extensor posturing or decerebrate rigidity. Instead of folding your hands onto your chest as you would in decorticate posturing, your hands are straight down by your sides. Your jaws are often clenched. Sometimes this only happens on one side, or only happens in the arms.

Decerebrate posturing is considered even worse than decorticate, for a couple of reasons. First, it shows up in response to a brain stem injury. Brain stem injuries are those that are going to have negative impactfulness, as the government guys say, on your ability to breathe, regulate your own blood pressure, and continue on living. Second, decerebrate posturing that shows up after a person's been doing decorticate posturing for a while indicates that the brain has just herniated down through the brainstem and the game's over.

Now, you can go back and forth from decorticate to decerebrate, but eventually, if you're not treated promptly and things like your intracranial pressure and brain injuries aren't stabilized, you're going to go all decerebrate on your own self and things will get very bad indeed.

Interestingly, I've seen quite a few cases where the patient has gone from decorticate to decerebrate posturing in a fairly short period of time. All of those cases were back when Sunnydale had a run on people with Creutzfeld-Jakob Disease (aka "Mad Cow", but without a cow involved--the normal CJD is a genetic thing). Everybody would start out a little disengaged, a little forgetful, a teeny bit aphasic. They would then progress to decorticate posturing in reponse to stimulus, then on to a really marked decerebrate posturing with the oddest, most eerie catlike meowing noises as a response to even gentle touch.

That last sentence just led me to sit, chin in hand, thinking about that two-year stretch of lots of CJD cases. And to be very glad I'm not doing as much of that any more. And to miss Sunnydale a bit.

Anybody got any fun ideas for Auntie Jo's next Oversimplification of Neuroscience lecture? Leave 'em in the comments!

10 comments:

Anonymous said...

I'd be interested in your comments on daily life postures and the importance, or not, of flexibility--for example, sitting up straight--does posture at the computer matter?; importance/nonimportance of walking as erect as possible; stretching (does the flexibility yoga aims for have any real benefits? I'm convinced that chanting Omm doesn't); pillows and positions while sleeping (thick or thin or doubled pillows good or bad, or it doesn't really matter, sleep is what counts?) Tummy sleeping, side or back sleeping, or it doesn't matter? I've always envied people who can bend over and put their hands flat on the floor--but do they have any advantages I don't? (Or should I just put that one in the category of Neener, neener, look how I can roll my tongue, and you can't?)
Anne
P.S. (And you may not want to discuss this--but if you do, I'm wondering--okay, it's none of my business, but I'm curious--about yawning, swimming, humming, yelling, whispering, spitting, brushing teeth, coughing, coughing up phlegm, etc., after your surgery.)

Anonymous said...

I used to always have to stop,think and then ask somebody else whether is was decorticate or decerabrate until a Dr told me to remember the "cor" or center and that's when the arms are into the center of the body.Never had to think and then worry if I had just charted the opposite of what I meant.

Wayne Conrad said...

I like your writing. It's clear, doesn't talk down, and I learn things. Thanks. And, no, this is not a spam comment :)

Oh, I was looking at the picture you posted prior, and wondering "just what the heck does the uvula do, besides making me wonder 'what does it _do?' "

Andrea said...

So what about the people with encephalopathic disorders - like post-status epilepticus and kind of a generally fubar'd brain but no stroke or other ICP issues - what about these folks that posture and have positive babinski's but then wake up and are extubated two days later? WTF? This happened to one of my patients this week and I don't understand. I hope I"m not being too vague. If you need more deets, I'm happy to post all of the nitty gritty in this person's neuro assessment. It just really blew my mind that they're extubated and awake and decently oriented after all that.

Jo said...

Andrea: Most times that sort of temporarily fubar-ed-ness can be put down to crazy neurotransmitter activity. I remember years ago learning about something called "swordfighter pose" or "fencer pose" or something like that--I do remember that it had to do with blades--that you'd see after a head injury in, say, a football game. The person who'd been hit in the head would be aaaalll jacked up, complete with abnormal posturing, and then be fine once the neurotransmitters released by the injury cleared.

Celeste said...

I've always wondered about amnesia. The soaps make it look like you can't go a year without somebody on the block having it, but I've only ever heard of it on tv. I assumed it was from a head injury. Illuminate me if you can; I assume if somebody had it they'd have to go to neuro for at least an exam, but maybe I'm even wrong on that.

Bonnie said...

Thanks! On to my next question (yes, I was the one who asked about this): what IS a herniated brain?

And I was under the impression that decorticate/decerebrate postures were 'permanent', that the body didn't move once it was stuck that way. But from what you're saying about stimuli, the body can be induced to move *into* the posture, then will move back out? Am I getting that right?

And I remember hearing about the swordfighter pose too...something about it and newborns too.

Anonymous said...

I'm just glad you're back.

Katherine said...

Hi, was wondering about brain herniation... If the brain is herniating downward out of the foramen magnum, wouldn't the brain stem below the level of the red nucleus be damaged first, then followed by damage to the brain stem above (and hence decerebrate posturing before decorticate posturing)? I'm struggling to understand why it goes decorticate to decerebrate. Thanks!

Anonymous said...

I'm a nursing student who was looking at this to try to help me learn decorticate and decerebrate. I knew someone with CJD as well. She went from normal one day to really off the next day and two weeks later, she was gone. Horrible disease, but very interesting. Thank you for the post. :)