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

6. General discussion and Summary
pain were found in our study population, aspects of the pattern of sensory signs did
differ between the highest and lowest level of certainty, i.e., between ‘definite’ and
‘probable’ neuropathic pain and ‘unlikely’ neuropathic pain. Previously, it was reported
that profiles of sensory signs differ even in the different clinical entities of neuropathic
pain (Maier et al 2010). Unfortunately, the 1236 neuropathic pain patients included
in that study were not analysed with respect to their neuropathic pain grades (Maier
et al 2010). Studies in large populations of patients with different clinical entities of
neuropathic pain and recognized neuropathic pain grades could evaluate the presence
of specific profiles of somatosensory signs. The identification of differences in patterns
of sensory abnormality in neuropathic pain patients could lead to a mechanistic
understanding of somatosensory abnormalities in neuropathic pain.
We reported earlier that in patients with unilateral neuropathic pain the presence
of contralateral sensory changes was correlated with the intensity of ongoing pain
(chapter 2). This was confirmed in a second study describing a larger and more diverse
neuropathic patient sample (chapter 3). When we categorized the patients with respect
to their certainty of neuropathic pain we found that this overall effect was driven
only by the group of patients graded as ‘definite’ neuropathic pain (r=0.642; p=0.01)
(unpublished data). This finding indicates that the greater the pain intensity the more
contralateral abnormalities occur, but only for the group of patients graded as ‘definite’
neuropathic pain.
In the same study we have also identified a mismatch between clinical diagnosis of
neuropathic pain and neuropathic pain grading. Only 60% of patients with clinically
diagnosed neuropathy were categorized as ‘definite’ and ‘probable’ neuropathic pain.
This is an interesting finding in the context of the recently revised neuropathic pain
definition. Accordingly, neuropathic pain is a direct consequence of a lesion or disease
affecting the somatosensory system (Treede et al 2008). The grading system complements
this definition and consequently 60% of our patients diagnosed as neuropathic pain
were also graded as neuropathic pain. To what extent abnormal function of the
somatosensory system oblige to this definition is in the context of our findings unclear.
Similar, it remains unclear if the neuropathic pain grading could improve the efficacy
in the treatment of neuropathic pain. However, this grading system certainly allows
a precise selection of patients for clinical research and is therefore an interesting tool
to translate findings into clinical practice and potentially increase patient’s treatment
satisfaction.
Implications of QST for clinical neuropathic pain research
The third study was designed to determine if QST would be a valid instrument to
identify somatosensory homogenous groups of patients with neuropathic pain (chapter
4). We found that a single QST parameter, i.e. mechanical pain sensitivity (MPS), can
be used to identify distinct subgroups of neuropathic pain patients. A part of the patients