77. Tactile Extinction

What is Being Tested? 

Somatosensory deficits can be caused by lesions in peripheral nerves, nerve roots, the posterior columns or anterolateral sensory systems in the spinal cord or brainstem, the thalamus, or sensory cortex. Recall that position and vibration sense ascend in the posterior column pathway and cross over in the medulla, while pain and temperature sense cross over shortly after entering the spinal cord and then ascend in the anterolateral pathway (see Figures 2.13, 2.18 and 2.19 in Neuroanatomy through Clinical Cases 3e). Intact primary sensation with deficits in cortical sensation such as agraphesthesia or astereognosis suggests a lesion in the contralateral sensory cortex. Note, however, that severe cortical lesions can cause deficits in primary sensation as well. Extinction with intact primary sensation is a form of hemineglect that is most commonly associated with lesions of the right parietal lobe. Like other forms of neglect, extinction can also occasionally be seen in right frontal or subcortical lesions, or in left hemisphere lesions causing mild right hemineglect.

The pattern of sensory loss can provide important information that helps localize lesions to particular nerves, nerve roots, and regions of the spinal cord, brainstem, thalamus, or cortex (see KCC 7.3 and Chapters 8 and 9 in Neuroanatomy through Clinical Cases 3e).