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 Devices 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 Devices 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 1-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.
"The two points discrimination test (2PD) (Figure 2) evaluates the density of reinnervation of large myelinated fibers of the skin receptors, through a pressure-specific sensory device (Aszmann & Dellon, 1998). This test correlates with nerve conduction velocity, although this depends on several factors such as age (Kaneko et al., 2005) and should be accompanied by a description of how the test was performed to quantify the tactile discrimination, in association of others tests (Jerosch-Herold, 2000; Jerosch-Herold, 2003; Lundborg & Rosén, 2004). "
"Four subjects (2 male, 2 female) were tested on a second occasion 7—10 days later. TPDA was measured according to the conventional protocol used by neurologists (see Dellon et al. 1987; Aszmann & Dellon, 1998). Two points of a pair of callipers were applied to the skin and the subject was asked to report whether they sensed one or two points. "
[Show abstract][Hide abstract] ABSTRACT: Neurological testing tools for measuring and monitoring somatosensory function lack resolution and are often dependent on the clinician testing. In this study we have measured perceptual threshold (PT) to electrical stimulation of the skin and compared it with two-point discriminative ability (TPDA) in 12 control subjects. Tests were made on both sides of the body at American Spinal Injury Association (ASIA) key points on seven spinal dermatomes (C3 (neck), C4 (shoulder), C5 (upper arm), C6 (thumb), T8 (abdomen), L3 (knee), L5 (foot)) and in the mandibular (chin) and maxillary (cheek) fields of the trigeminal (V) nerve. Electrical stimulation (0.5 ms pulse width; 3 Hz) was applied via a self-adhesive cathode and an anode strapped to the wrist or ankle. The stimulus intensity was adjusted and PT was recorded as the lowest current at which the subject reported sensation. Sites were tested in random order. Indices for both TPDA and PT differed according to the dermatome tested but there was no correlation between TPDA and PT for any dermatome. There was good correlation between results from equivalent dermatomes on left and right sides for both PT and TPDA. Women frequently had lower mean (± s.e.) PTs and better TPDA than men; differences were significant (P < 0.05) for PT on the knee (women, 1.31 ± 0.15 mA; men, 2.05 ± 0.26 mA) and the foot (women, 2.90 ± 0.19 mA; men, 4.13 ± 0.28 mA) and for TPDA on the thumb (women, 3.8 ± 0.2 mm; men, 7.8 ± 1.3 mm) and the knee (women, 17.8 ± 1.6 mm; men, 27.1 ± 4.0 mm). Four subjects repeated the experiment on another day and the results correlated well with the first test for PT (r2, 0.62) and TPDA (r2, 0.48). PT differs between dermatomes in a predictable way but does not relate to TPDA. PT is easy to measure and may be a useful assessment tool with which to monitor recovery or deterioration in neuropathies, neurotrauma or after surgery.
[Show abstract][Hide abstract] ABSTRACT: Static two-point discrimination (2PD) has been relied upon clinically to gauge the extent of median neuropathy in patients with carpal tunnel syndrome (CTS). Correlation with median nerve sensory conduction findings has not been well-established. We determined the median sensory nerve action potential parameters from the first and third digits of 83 hands referred primarily for suspected CTS. These results were compared to 2PD carried out in a standardized fashion by a group of hand surgeons. A lack of correlation was found in most electrodiagnostic parameters, with the exception of peak and onset latencies to the thumb; on further analysis, 2PD to the thumb was found to be useful if abnormal, but contributed nothing if negative. We conclude that static 2PD results may correlate with latency, but do not overall adequately predict the findings on sensory nerve conduction examination of the median nerve.
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