Patients diagnosed with complex regional pain syndrome type I of the upper limb

Patients diagnosed with a neuropathy of the median nerve of the upper limb.

Healthy adult persons.

For a detailed description of the methods see "outcome measures"

Thresholds on the tip of the index finger of boths hands are assessed using the method of constant stimuli. One single needle and seven pairs of needles with different spacings are tested in randomized order. After each presentation, the subject has to report the sensation of one or two needles by answering immediately "one" or "two." Each distance is presented eight times resulting in 64 single decisions. The summed responses are plotted against distance as a psychometric function for absolute threshold and get fitted by a binary logistic regression. Thresholds are taken from the fit at the distance at which 50% correct answers are given

Stimuli are taken from a set of dome-shaped plastic gratings with equal groove and ridge widths. Gratings are applied to the immobilized distal fingerpad of the index finger of boths hand with the ridges oriented either along or across the long axis of the finger in randomized sequences of the two alternatives. Subjects have to report the orientation of the gratings as "along" or "across". The largest groove widths in the set is 6mm, the minimal width is 0.5mm. Thresholds were taken from the groove width at which the performance was 75% correct. Unless the performance is exactly 75% for a particular grating, interpolation between gratings spanning the 75% correct responses ared used

Touch thresholds are taken from a set of von Frey filaments (0.25 mN - 512 mN). Touch sensitivity is investigated by using a staircase procedure during which subjects are required to close their eyes and report when they perceive an indentation of the skin on the fingerpad of the index finger. The applied forces are decreased in a stepwise manner until the subject no longer perceives the stimulus (lower boundary) and then increased until the stimulus is perceived again (upper boundary). This procedure is repeated 5 times resulting in 10 values that are averaged to provide the touch threshold.