Ecological aspects of pain in sensory modulation disorder.

BACKGROUND: Sensory Modulation Disorder (SMD) interferes with the daily life participation of otherwise healthy individuals and is characterized by over-, under- or seeking responsiveness to naturally occurring sensory stimuli. Previous laboratory findings indicate pain hyper-sensitivity in SMD individuals suggesting CNS alteration in pain processing and modulation. However, laboratory studies lack ecological validity, and warrant clinical completion in order to elicit a sound understanding of the phenomenon studied. Thus, this study explored the association between sensory modulation and pain in a daily life context in a general population sample. METHODS: Daily life context of pain and sensations were measured in 250 adults (aged 23-40 years; 49.6% males) using 4 self-report questionnaires: Pain Sensitivity Questionnaire (PSQ) and Pain Catastrophizing Scale (PCS) to evaluate the sensory and cognitive aspects of pain; the Sensory Responsiveness Questionnaire (SRQ) to appraise SMD; and the Short Form - 36 Health Survey, version 2 (SF36) to assess health related Quality of Life (QoL). RESULTS: Thirty two individuals (12.8%) were found with over-responsiveness type of SMD, forming the SOR-SMD group. While no group differences (SOR-SMD vs. Non-SMD) were found, low-to-moderate total sample correlations were demonstrated between the SRQ-Aversive sub-scale and i) PSQ total (r=0.31, p<0.01) and sub-scales scores (r=0.27-0.28, p<0.01), as well as ii) PCS total and the sub-scales of Rumination and Helplessness scores (r=0.15, p<0.05). PSQ total and sub-scale scores were more highly correlated with SRQ-Aversive in the SOR-SMD group (r=0.57-0.68, p=0.03-<0.01) compared to Non-SMD group. The Physical Health - Total score (but not the Mental Health - Total) of the SF36 was lower for the SOR-SMD group (p=0.03), mainly due to the difference in the Body pain sub-scale (p=0.04). CONCLUSIONS: Results suggest that SOR-SMD is strongly associated with the sensory aspect of pain but weakly associated with the cognitive aspect. This indicates that SMD co-occurs with daily pain sensitivity, thus reducing QoL, but less with the cognitive-catastrophizing manifestation of pain perception.

Atypical central pain processing in sensory modulation disorder: absence of temporal summation and higher after-sensation.

Sensory over-responsivity (SOR), a subtype of the proposed sensory modulation disorder (SMD), is characterized by over-responsiveness to stimuli in several sensory modalities. SMD individuals demonstrate abnormal responses to naturally occurring stimuli in a manner that interferes with daily life participation. Previous psychophysical testing of the somatosensory system revealed that SOR individuals rated pain sensations higher than controls, demonstrating hyperalgesia that can be centrally mediated. Temporal summation (TS) of second pain and after-sensation are manifestations of central sensitization; therefore, this study explored these measures for better characterization of central pain processing in SOR. Twelve SOR adults and 12 healthy controls participated. TS was produced by a train of fifteen repetitive heat pulses, 0.7 s duration each, and 2 s of inter-stimulus interval, applied to the thenar-eminence, while four pain ratings were obtained. An after-sensation was then measured for 5 min, obtaining six pain ratings. No TS of pain was indicated in the SOR group (SOR: p = 0.36; control: p < 0.001). Further, while controls reported a gradual disappearance of pain after-sensation, individuals with SOR continued to report pain for the duration of the 5 min measured (p = 0.002). These results demonstrate an atypical response pattern, suggesting alteration in pain processing and/or modulation at a central level in individuals with SOR. These possible neural changes may manifest themselves as interference with daily functioning as well as shed light on some of the between-subject variability seen in psychophysical testing in non-painful subjects.