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

1. General introduction
Table 1-2: Simplified overview of nerve fibres sub-modalities tested by QST
QST
parameter
C-fibre
Aδ-fibre
Aβ-fibre
CPT HPT WDT WUR CPT TSL PHS MPT MPS MDT DMA VDT PPT
X X X X
X
X X X X X
X
X X X
Potential overlapping modalities for each nerve fibre type are not shown. QST parameters are:
Cold Pain Threshold (CPT), Heat Pain Threshold (HPT), Warm Detection Threshold (WDT), Wind
Up Ratio (WUR), Cold Detection Threshold (CDT), Thermal Sensory Limen (TSL), Paradoxical
Heat Sensation (PHS), Mechanical Pain Threshold (MPT), Mechanical Pain Sensitivity (MPS),
Mechanical Detection Threshold (MDT), Dynamic Mechanical Allodynia (DMA), Vibration
Disappearance Threshold (VDT) and Pressure Pain Threshold (PPT). All nerve fibre functionality
tests are applied to the skin with exception of PPT (deep tissue C-fibre/Aδ-fibre test).
1.2.1. QST and homogenous groups of somatosensory abnormalities
QST might offer a tool to identify homogenous groups of somatosensory abnormalities
in patients with neuropathic pain for the evaluation of novel pain compounds. The
approach currently used in clinical trials is the assessment of general pain relief values
for specific aetiologies, which might partially explain the failure to obtain complete
pain relief in neuropathic pain conditions (Baron 2006). This is in line with the Food
and Drug Administration (FDA) that requests the inclusion of patient populations for
clinical trial based on disease endpoints for the registration of pain medication. More
pragmatic in the current environment is to use a disease endpoint recognised by the
FDA but to reduce heterogeneity in the patient group in order to reduce variability in
the trial and increase the power. A classification based on sensory abnormalities rather
than based merely on aetiology could contribute to minimising pathophysiological
heterogeneity within study groups (Attal et al 2008). Such an approach would recognise
not only pain as an outcome measure but also addresses troublesome features such
as hyperalgesia and allodynia frequently reported by patients with neuropathic pain.
There is a need for a different method of evaluating pain medications to increase
positive treatment responses e.g. increase assay sensitivity. QST-based identification
of homogenous patient populations could help to clarify the relationships between
the aetiology and somatosensory abnormalities in neuropathic pain patients. This is a
particularly interesting approach when such groups of somatosensory-wise homogenous
pain patients are investigated further with e.g. neuroimaging techniques to reveal
potential group-specific changes in the brain.
Human brain imaging studies show that structural changes and brain function changes
in different neural regions including the thalamus, nucleus accumbens, basal ganglia,