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

6. General discussion and Summary
QST in clinical practice; general considerations
Studies suggest that up to 5% of individuals undergoing surgery will develop severe
persisting pain (Kehlet et al 2006; Poleshuck & Green 2008). In a number of studies,
pre-existing pain and high-intensity post-operative pain have been the predictors of
development of persisting pain after surgery (Bisgaard et al 2005; Katz et al 2005;
Pluijms et al 2006; Poleshuck et al 2006). Another patient study showed that assessing the
sensory characteristics of cancer-induced bone pain prior and after radiotherapy allows
the identification in alterations in sensory responses. Alterations in specific sensory
characteristics (e.g. abnormal warm sensation and pinprick pain) were associated with
an increased likelihood of successful analgesia from palliative radiotherapy (Scott
et al 2011). Individual differences in evoked pain sensitivity as potentially important
prospective predictors of the course of clinical pain complaints have been suggested
also in other studies. For example, pre-operative supra-threshold pain stimuli at 44 ºC
- 48 ºC responses, but not heat pain thresholds predicted post-operative pain scores in
women undergoing caesarean section (Granot et al 2003).
Sensory testing can be also used as an outcome measure to document treatment-related
changes in somatosensory function. For example, opioid-induced hyperalgesia refers to
a phenomenon whereby opioid administration results in a lowering of pain thresholds,
clinically manifest as apparent opioid tolerance and worsening pain despite accelerating
opioid doses. Recently, we proposed that sensory testing could help to identify opioidinduced
hyperalgesia and subsequently its differentiation from tolerance (Konopka
& van Wijhe 2010). This is clinically important, since tolerance can be overcome by
dose escalation, whilst opioid-induced hyperalgesia may be aggravated by the same
intervention. We have suggested that sensory testing should be performed prior to the
anaesthesia at an area distant from the surgery site and subsequently up to a few hours
post-operatively. Another aspect which has not been investigated is the situation that
disease progression induces changes of sensory thresholds. If such changes occur and
sensory abnormalities are present pre-operatively this in turn could blur post-operative
sensory outcome measures and therefore might compromise the investigation of opioidinduced
hyperalgesia. In this context, reference values from healthy subjects could be
used to establish normal sensory functioning in patients prior to anaesthesia.
In conclusion, utilizing QST as a tool to assess sensory function does make sense, not
only in patients with chronic pain but also in healthy subjects. In this thesis we have
investigated the applicability of QST in clinical practice and for research purposes. In
these studies we provide evidence that QST can lead to an improved characterisation
of sensory signs in unilateral neuropathic pain, an improved understanding of
sensory function in patients with different neuropathic pain grades and an improved
understanding of somatosensory function as a pain-contributing factor in patients
with patellar tendinopathies. QST also allows the identification of homogenous patient
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