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

6. General discussion and Summary
sensory function and its clinical manifestation can differ when either the contralateral
side or the healthy volunteer data is used. To avoid potential misjudgement of the quality
of sensory abnormalities we suggest that only QST reference values obtained from
healthy controls are used.
In this context it is unknown to which extent the potential misinterpretation of sensory
signs in neuropathic pain patients might have contributed to the lack of efficacy observed
in the treatment of neuropathic pain. Based on our data, a direct comparison between
the effects of treatment on sensory signs established with either bedside tests or the use
of reference data would be useful.
Assessing patients using the elaborate QST protocol can be very time-consuming and
demanding for both patient and physician. For the assessments, patients need to be
repositioned frequently to allow a correct application of stimuli. Thus, commonly a
complete evaluation of the affected site of neuropathic pain patients takes more than 45
minutes. Such time- and labour intensive evaluation of somatosensory abnormalities
limits QST for regular usage in the clinic. Indeed, the QST protocol needs to be
simplified to become a regular screening tool in a clinical setting. In this context, it is
of interest to identify the most sensitive QST parameters to determine somatosensory
specifics for each neuropathic pain entity.
To facilitate the diagnosis neuropathic pain, recently, a grading system was introduced
by which the patient’s pain can be categorized as definite, probable, possible or unlikely
neuropathic pain (Treede et al 2008). This grading system is aimed to determine with a
greater level of certainty whether a pain condition is neuropathic.
We applied this grading system in a group of neuropathic pain patients and compared
the results with those of the standardized QST protocol (chapter 3). Our findings show
that the number of sensory abnormalities do not correspond with a greater level of
certainty whether a pain condition is neuropathic, i.e., the number of somatosensory
abnormalities were not different between the various grades of neuropathic pain.
This result is striking since the presence of somatosensory abnormalities is a major
aspect of neuropathic pain, which would predict that the more certain the diagnosis of
neuropathic pain the greater the number of abnormalities. However, our results indicate
that irrespective of the degree of neuropathic pain the somatosensory response e.g.
numbers of abnormalities is similar for all diagnosis levels of certainty. In this context
it would be interesting to investigate somatosensory abnormalities in non-neuropathic
chronic pain diseases such as fibromyalgia and complex regional pain (CRPS-1) in
greater detail. Similarities in the frequency of QST abnormalities to those observed
in neuropathic pain patients might point towards a “common final path” for the
somatosensory system in chronic pain diseases.
Whereas similar numbers of sensory abnormalities for the different grades of neuropathic