Hyper-reflexia without spasticity after unilateral infarct of the medullary pyramid

Whether or not a lesion confined to the pyramidal tract produces spasticity in humans remains an unresolved controversy. We have studied a patient wit h an ischemic lesion of the right medullary pyramid, using objective measur es of hyper-reflexia, spasticity, and weakness. Electromyographic activity (EMG) of the biceps muscles was recorded under the following conditions: (1 ) in response to a tendon tap with an instrumental reflex hammer, (2) in re sponse to imposed quick stretch with motion analysis, and (3) during an iso metric holding task. Hyper-reflexia of the involved arm in response to tend on tap was shown to be due primarily to an increase in the gain of the refl ex are. No velocity-dependent increase in the response to quick stretch of the involved arm was present. This was consistent with the absence of detec table spasticity on the clinical exam. These findings suggest that a lesion confined to the medullary pyramid can give rise to weakness and hyper-refl exia without causing spasticity. Moreover, these findings suggest that diff erent anatomical substrates may underlie the clinical phenomena of hyper-re flexia and spasticity. (C) 2000 Elsevier Science BN. All rights reserved.