RELATIONSHIP BETWEEN CUTANEOUS PRESSURE THRESHOLD AND 2-POINT DISCRIMINATION

The amount of pressure that should be applied when doing the two-point discrimination test has always been a matter of controversy. The Pres sure-specified Sensory Device(TM) permits recording the pressure at wh ich two-point discrimination (2 PD) occurs. The purpose of this study was to investigate the relationship between the cutaneous pressure thr eshold and 2PD in people with normal and abnormal peripheral nerve fun ctions. The Pressure-specified Sensory Device(TM) was used to quantify the cutaneous pressure threshold in the index-finger pulp in each ind ividual, between the range of 2 mm and 8 mm of static 2 PD, using l-mm intervals. Twenty normal controls were examined; ten patients were le ss than 45 years of age; and ten patients were greater than 45 years o f age. This relationship of pressure to 2PD was also tested in eight p atients with abnormal peripheral nerve function (four patients with ca rpal tunnel syndrome, and four patients with diabetic neuropathy). A c urvilinear relationship was identified in which, for the same skin sur face in the same individual, regardless of age or presence of nerve co mpression or neuropathy, the cutaneous pressure threshold was inversel y related to static 2PD. This curve shifted upward and to the right wi th the increasing age of the normal population and with neurologic imp airment. The awareness of this neurophysiologic relationship between 2 PD and pressure threshold permits the design of strategies for sensibi lity testing and provides a basis for the interpretation of sensory te st results.