Psychophysical correlates in children with sensory modulation disorder (SMD)

Sensory modulation disorder (SMD), affecting approximately 5% of children, is characterized by sensory over or under-responsiveness to a range of stimuli in several modalities. Children with over-responsiveness (SOR) demonstrate increased aversion to certain natural stimuli that manifests as increased distress and avoidance behaviors to common stimuli, accompanied by abnormal electrodermal responses and brain evoked potentials to various stimuli. This study is the first to use quantitative sensory testing to characterize the somatosensory sub-modalities of children with SMD. Seventy eight children aged 6-10 years (44 SMD children and 34 classmate controls) were tested. A diagnosis of SMD and SMD-free using the Short Sensory Profile was ascertained by the Sensory Profile Questionnaire, both completed by participants' mothers. Sensory detection thresholds for skin warming, cooling, punctate dynamic tactile sensation, vibration and thermal pain thresholds for heat and cold were determined at several body sites. Pain and prickle intensities for pinprick and prickly stimuli and the duration and intensity of the after-sensations of prickliness and pain evoked by the prickle stimuli were assessed. Compared to the control children, SMD children showed significant cool hypoesthesia, higher pain intensity to pinprick and to prickly stimuli, and significantly more pain after-sensation to the prickly stimuli. No significant differences between groups were found in most of the sensory and pain thresholds at any tested site. These results indicate, for the first time, that children with SMD perceive more pain, and that their pain lasts longer. Our results demonstrate that SOR does not imply lowered sensory thresholds but abnormal processing suprathreshold noxious stimuli.