Quantitative Sensory Testing (QST) - Does assessing ... - TI Pharma
Quantitative Sensory Testing (QST) - Does assessing ... - TI Pharma 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.
4. QST and neuropathic pain mechanisms Fig. 4-1: Mechanical Pain Sensitivity (MPS) stimulus-response functions for neuropathic pain patients (n=16). Patients with MPS z-score values outside of the 95% CI showed a stimulus-response function to pinpricks. Stimulus-response functions were assessed by seven pinpricks exerting forces of 8mN, 16mN, 32mN, 64mN, 128mN, 256mN and 512mN. Each data point represents mean value for numerical rating scale (NRS (0-100)) for the painfulness of five stimulations for each pinprick force. The two groups of patients with differences in their stimulus-response function were further evaluated. The linear fit analyses for each subject identified differences in the slope for the stimulus response function. For patients with a stimulus-response function the mean slope of the NRS for pain was 5.78 and for other patient group the NRS mean slope was 1.31 (Fig. 4-3). Significant differences between these slopes was confirmed by t-test (t=7.532, df = 39, p < 0.001). This result shows that two different types of responders to the pinprick stimulus-response function are present within the neuropathic pain patient population that show abnormal function in the MPS test.
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4. <strong>QST</strong> and neuropathic pain mechanisms<br />
Fig. 4-1: Mechanical Pain Sensitivity (MPS) stimulus-response functions for neuropathic pain<br />
patients (n=16). Patients with MPS z-score values outside of the 95% CI showed a stimulus-response<br />
function to pinpricks. Stimulus-response functions were assessed by seven pinpricks exerting<br />
forces of 8mN, 16mN, 32mN, 64mN, 128mN, 256mN and 512mN. Each data point represents mean<br />
value for numerical rating scale (NRS (0-100)) for the painfulness of five stimulations for each<br />
pinprick force.<br />
The two groups of patients with differences in their stimulus-response function were<br />
further evaluated. The linear fit analyses for each subject identified differences in<br />
the slope for the stimulus response function. For patients with a stimulus-response<br />
function the mean slope of the NRS for pain was 5.78 and for other patient group the<br />
NRS mean slope was 1.31 (Fig. 4-3). Significant differences between these slopes was<br />
confirmed by t-test (t=7.532, df = 39, p < 0.001). This result shows that two different<br />
types of responders to the pinprick stimulus-response function are present within the<br />
neuropathic pain patient population that show abnormal function in the MPS test.
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