Sensory Over-Responsiveness among Healthy Subjects is Associated with a Pronociceptive State.

Abstract

Chronic pain patients show hypersensitivity to sensory nonpainful stimuli. Sensory over-responsiveness (SOR) to innocuous daily stimuli, experienced as painful, is prevalent in 10% of the healthy population. This altered sensory processing may be an expression of overfacilitation, or a less efficient pain-inhibitory process in the pain pathways. We therefore aimed to investigate specifically the pain-inhibitory system of subjects with SOR who are otherwise healthy, not studied as of yet. Thirty healthy subjects, divided into an SOR group (n=14) and a non-SOR group (n=16) based on responses to the Sensory Responsiveness Questionnaire, were psychophysically tested in order to evaluate (1) hyperalgesic responses; (2) adaptation/sensitization to 14 phasic heat stimuli; (3) habituation; (4) 6-minute after-sensations; and (5) conditioned pain modulation (CPM) (ie, phasic heat stimuli applied with and without hand immersion in a hot water bath). The SOR group differed from the non-SOR group in (1) a steeper escalation in NPS ratings to temperature increase (P=0.003), indicating hyperalgesia; (2) increased sensitization (P<0.001); (3) habituation responses (P<0.001); (4) enhanced pain ratings during the after-sensation (P=0.006); and (5) no group difference was found in CPM. SOR is associated with a pronociceptive state, expressed by amplification of experimental pain, yet with sufficient inhibitory processes. Our results support previous findings of enhanced facilitation of pain-transmitting pathways but also reveal preserved inhibitory mechanisms, although they were slower to react.