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

4. QST and neuropathic pain mechanisms
4.3. QST for mechanism-based studies in neuropathic pain patients
QST data can be regarded as a rich source of valuable information of sensory
abnormalities in chronic pain patients such as neuropathic pain. It is striking that
sensory abnormalities for certain parameter such as Pressure Pain Threshold (PPT)
or Mechanical Pain Sensitivity (MPS) of the QST battery were by far more frequently
observed than others. The prevalence of sensory gain for PPT and MPS overall in
neuropathic pain patients was reported to be 36.4% and 29.2%, respectively (Maier et
al 2010).
The identification of somatosensory phenotypes based on single QST parameter
such as MPS can contribute to the viability of mechanism-based understanding of
neuropathic pain. We showed that different “responders” to MPS exist in the population
of neuropathic pain patients. From a mechanistic point of view the identification of
phenotypical homogenous groups of different “responders” for even a single QST
parameter e.g. MPS might be useful. Future studies could evaluate if these different
responders show differences in pharmacological responsiveness using different classes
of pharmacological agents, e.g. sodium-channel blocker, antidepressants. In addition,
if differences in responders to other QST parameters could be identified, with again
distinct reactions to pharmacological interventions, a truly mechanistic picture of the
somatosensory of neuropathic pain patients could be emerging. As previous mentioned,
looking at QST profiles instead of a single parameter has shown its value to generate a
mechanistic understanding of somatosensory abnormalities in neuropathic pain (Maier
et al 2010). Our results add to that finding that one can even further subdivide the
patients based on more detailed testing as we did using our specific MPS analysis
approach.
Our results indicate that multiple mechanisms e.g. different causes of neuropathic
pain, can lead to the same sensory sign e.g. MPS abnormalities. Moreover, that distinct
different pattern of sensitisation to pinprick pain is common in different neuropathic
pain aetiologies. This observation raises the question if these mechanistic differences in
sensitisation could also explain the lack of efficacy of pharmacotherapy in neuropathic
pain patients.
In summary, a single QST parameter, i.e. MPS, can be used to identify distinct subgroups
of neuropathic pain patients, characterised by altered mechanical pain sensitivity.
Part of the patients showed a clear stimulus-response to pinprick stimuli, while in the
other part a stimulus-response to pinprick stimuli was completely absent. Both types
of responses were found within different clinical entities of neuropathic pain. Further
evaluation is necessary to identify potential differences in the mechanisms responsible
for these distinct MPS abnormalities and their subsequent mechanism-based therapy.