Re: Corticospinal Tract Lesions

Posted By CCF Neurology W6 MD on November 20, 1998 at 18:13:32:

In Reply to: Corticospinal Tract Lesions posted by Jon Moore on November 20, 1998 at 17:58:05:






I am a neurology student in Sydney Australia. I do not understand why a
corticospinal tract lesion will result in decreased deep tendon reflexes
(DTR's) when it is actually an UMN lesion. I assume it has something to do
with the fact that there is no specific cortical control over the muscle,
and the background tone is increased from the extrapyramidal system, but
if it is a reflex loop, the alpha motor neurone is still in tact so surely
the DTR loop will still fire.
Jon Moore
    =
Dear Jon,
thank you for the question. I am not sure where you read that, or it may be a misprint. But UMN or lesion along the corticospinal tract causes increase or hyperactivity of the DTR along with Babinski sign (extensor plantar reflex). In practice however, I have seen DTR's that is difficult to elicit in someone who has contracture from an old  UMN lesion, i.e. with flexed elbow (contracture at the elbow) the biceps reflex may be difficult to get, or those with contracture at the knee, the knee jerk is difficult to elicit.
I hope the above information helps and good luck with your study.