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Modulatory influence on somatosensory perception from vibration & heterotopic noxious conditioning stimulation (HNCS) in fibromyalgia (FM) patients & healthy subjects

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In order to assess the function of endogenous mechanisms modulating
somatosensory input in fibromyalgia (FM), the effect of
vibratory stimulation (VS) and heterotopic noxious
conditioning stimulation (HNCS) on perception of various
somatosensory modalities was assessed.

Ten female FM patients and 10 healthy, age-matched, females
participated. VS (100 Hz) was applied to the left forearm for 45 min
and quantitative sensory testing (QST) was performed within the
vibrated area and in the right thigh before, during and 45 min following
vibration. Pressure pain thresholds (PPTs) were assessed by
pressure algometry. Perception thresholds to non-painful cold
(CT) and warmth (WT), heat pain thresholds (HPTs), cold pain
thresholds (CPTs) and stimulus-response curves of pain
intensity as a function of graded nociceptive heat stimulation
were assessed using a Peltier element based thermal
stimulator. The effects of HNCS were tested using the upper
extremity submaximal effort tourniquet test. Subjects rated
tourniquet induced pain intensity on a visual analogue scale
(VAS). QST was performed in the right thigh before, during and
60 min following the tourniquet.

FM patients did not differ from controls in the response to VS. There
was a local increase of PPTs during vibration (P < 0.001) and of WTs
following vibration (P < 0.001). HPTs increased in the forearm
and in the thigh (P < 0.009) during vibration. CTs and
sensitivity to suprathreshold heat pain were not influenced by
VS. The intensity of pain induced by the tourniquet did not
differ between groups. PPTs increased during the tourniquet in
controls (P < 0.001) but not in FM patients (difference
between groups P < 0.001). Decreased sensitivity to
non-painful cold (P < 0.001) and non-painful warmth (P <
0.001) was seen during and following (P < 0.001; P < 0.05,
respectively) the tourniquet in both groups alike. HPTs and
perception of suprathreshold heat pain remained unaffected in
both groups.

In conclusion, FM patients did not differ from healthy controls in their
response to vibration, but no modulation of pressure pain was induced
by HNCS, as opposed to controls, suggesting a dysfunction in systems
subserving 'diffuse noxious inhibitory controls' (DNIC).

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