Relationship between cutaneous pressure threshold and two-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 Pressure-specified Sensory Device(TM) permits recording the pressure at which two-point discrimination (2 PD) occurs. The purpose of this study was to investigate the relationship between the cutaneous pressure threshold and 2PD in people with normal and abnormal peripheral nerve functions. The Pressure-specified Sensory Device(TM) was used to quantify the cutaneous pressure threshold in the index-finger pulp in each individual, 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 less than 45 years of age; and ten patients were greater than 45 years of age. This relationship of pressure to 2PD was also tested in eight patients with abnormal peripheral nerve function (four patients with carpal tunnel syndrome, and four patients with diabetic neuropathy). A curvilinear relationship was identified in which, for the same skin surface in the same individual, regardless of age or presence of nerve compression or neuropathy, the cutaneous pressure threshold was inversely related to static 2PD. This curve shifted upward and to the right with the increasing age of the normal population and with neurologic impairment. The awareness of this neurophysiologic relationship between 2PD and pressure threshold permits the design of strategies for sensibility testing and provides a basis for the interpretation of sensory test results.