Objectives: Impaired left/right judgment of the affected body part is regarded as a disruption of the body's representation in cortical and subcortical somatosensory and motor areas and has previously been demonstrated in patients with severe neuropathic pain states. It remains unknown whether persistent but less severe pain states are sufficient to induce a similar impairment.
Methods: Twenty-seven patients with unilateral carpal tunnel syndrome (CTS) and 27 healthy matched subjects performed 4 visual left/right judgment tasks. Series of pictures of hands, feet, and necks from 4 different views were presented at 6 rotation angles. Participants had to decide as accurately and quickly as possible whether a right or left body part was presented (for hands and feet) or whether the pictured neck was rotated toward the right or left. To control for a generalized impairment in mental rotation, a recognition task for Shepard-Metzler figures was included.
Results: Recognition time for all tasks was comparable between participants with CTS and healthy participants (P>0.47). However, participants with CTS were ∼10% less accurate in recognizing their affected hand (P=0.008). Recognition accuracy was also reduced for necks (P=0.019) but not for feet or Shepard-Metzler figures (P>0.69).
Discussion: This study demonstrates that individuals with CTS present with a selective impairment in left/right judgment that is restricted to the affected quadrant. This indicates that left/right judgment is impaired in much less severe pain states than previously demonstrated. The findings are in line with previous reports, which suggested the presence of central mechanisms in patients with CTS.