Quantitative Sensory Testing (QST) - Does assessing ... - TI Pharma

4. QST and neuropathic pain mechanisms
Table 4-1: Overview of pain ratings for Mechanical Pain Sensitivity (MPS) in healthy subjects
Mechanical Pain Sensitivity (MPS) stimulus-response functions for healthy controls (n=185).
Controls are divided in two age groups (45: age range 45-74 years).
MPS assessment took place at dorsal hand (hand) and dorsal foot (foot). Stimulus-response
functions were assessed by seven pinpricks exerting forces of 8mN, 16mN, 32mN, 64mN, 128mN,
256mN and 512mN. Each subject rated the painfulness of each stimulus by Numerical Pain Rating
(NRS) (0 no pain – 100 most imaginable pain). Geometric means of each value of five stimulations
for each pinprick force were pooled and 95% CI are presented.
3.2. Z-score transformation for MPS in patients
From the 127 chronic pain patients investigated, 87 (68.5%) patients did not exceed the
CI 95% of the z-score transformation and were regarded as normal responders to the
test of MPS. 40 patients (31.5%) exceeded the CI 95% of the z-score transformation.
None of the patient’s z-score was greater than -1.96 indicating the presence of only
sensory gain for MPS.
3.3. Differences in pattern of stimulus-response function
Investigating the stimulus response function of patients with MPS abnormalities revealed
two distinctive groups of responders to pinprick stimulations. 40% of patients with
abnormal z-score showed a stimulus-response function for MPS (Fig. 4-1). Generally, in
these patients an increase in the pinprick force resulted in an increase in pain response
(NRS). In contrast, such stimulus dependent response in pain ratings was absent in
60% of patients with MPS abnormalities (Fig. 4-2). Instead, patients consistently rated
each individual pinprick force equally painful indicating an “all or none” phenomenon.
Both patterns of pinprick responses in patients indicate a left-ward shift in painfulness
compared to healthy controls and can be regarded as pinprick hyperalgesia.