Samar Hatem

Value of quantitative sensory testing in neurological and pain disorders: NeuPSIG consensus

Summary Standards for conducting quantitative sensory testing (QST), which is a psychophysical method used to quantify somatosensory function in response to controlled stimuli in healthy subjects and patients, is discussed, and recommendations on the basis of current status of QST are presented. ABSTRACT Quantitative sensory testing (QST) is a psychophysical method used to quantify somatosensory function in response to controlled stimuli in healthy subjects and patients. Although QST shares similarities with the quantitative assessment of hearing or vision, which is extensively used in clinical practice and research, it has not gained a large acceptance among clinicians for many reasons, and in significant part because of the lack of information about standards for performing QST, its potential utility, and interpretation of results. A consensus meeting was convened by the Neuropathic Pain Special Interest Group of the International Association for the Study of Pain (NeuPSIG) to formulate recommendations for conducting QST in clinical practice and research. Research studies have confirmed the utility of QST for the assessment and monitoring of somatosensory deficits, particularly in diabetic and small fiber neuropathies; the assessment of evoked pains (mechanical and thermal allodynia or hyperalgesia); and the diagnosis of sensory neuropathies. Promising applications include the assessment of evoked pains in large‐scale clinical trials and the study of conditioned pain modulation. In clinical practice, we recommend the use QST for screening for small and large fiber neuropathies; monitoring of somatosensory deficits; and monitoring of evoked pains, allodynia, and hyperalgesia. QST is not recommended as a stand‐alone test for the diagnosis of neuropathic pain. For the conduct of QST in healthy subjects and in patients, we recommend use of predefined standardized stimuli and instructions, validated algorithms of testing, and reference values corrected for anatomical site, age, and gender. Interpretation of results should always take into account the clinical context, and patients with language and cognitive difficulties, anxiety, or litigation should not be considered eligible for QST. When appropriate standards, as discussed here, are applied, QST can provide important and unique information about the functional status of somatosensory system, which would be complementary to already existing clinical methods.

Abnormal Pressure Pain, Touch Sensitivity, Proprioception, and Manual Dexterity in Children with Autism Spectrum Disorders.

Children with autism spectrum disorders (ASD) often display an abnormal reactivity to tactile stimuli, altered pain perception, and lower motor skills than healthy children. Nevertheless, these motor and sensory deficits have been mostly assessed by using clinical observation and self-report questionnaires. The present study aims to explore somatosensory and motor function in children with ASD by using standardized and objective testing procedures. Methods. Tactile and pressure pain thresholds in hands and lips, stereognosis, proprioception, and fine motor performance of the upper limbs were assessed in high-functioning children with ASD (n = 27) and compared with typically developing peers (n = 30).  Results. Children with ASD showed increased pain sensitivity, increased touch sensitivity in C-tactile afferents innervated areas, and diminished fine motor performance and proprioception compared to healthy children. No group differences were observed for stereognosis. Conclusion. Increased pain sensitivity and increased touch sensitivity in areas classically related to affective touch (C-tactile afferents innervated areas) may explain typical avoiding behaviors associated with hypersensitivity. Both sensory and motor impairments should be assessed and treated in children with ASD.

Assessment of spinal somatosensory systems with diffusion tensor imaging in syringomyelia

Objective: The use of diffusion tensor imaging with three-dimensional fibre tracking (DTI-FT) was tested for the assessment of spinal sensory tract lesions. The relationships between tract lesions quantified with DTI-FT were systematically examined, and somatosensory dysfunction was assessed with quantitative sensory testing (QST) and laser-evoked potentials (LEP), in patients with syringomyelia. Methods: 28 patients with cervical syringomyelia and thermosensory impairment of the hands, and 19 healthy volunteers, were studied. A DTI-FT of the spinal cord was performed, focusing on the upper segment (C3–C4) of the syrinx. Three-dimensional DTI-FT parameters (fractional anisotropy (FA) and apparent diffusion coefficient (ADC)) of the full, anterior and posterior spinal cord were individually compared with QST (thermal detection thresholds) and LEP (amplitude, latency and spinothalamic tract (STT) conduction time) of the hands. Results: Patients had a significantly lower FA, but not ADC, than healthy subjects. The mean FA of the full section of the spinal cord was correlated both to sensory deficits (ie, increase in warm (rho = −0.63, p<0.010) and cold thresholds (rho = −0.72; p<0.001 of the hands)) and to changes in LEP parameters, in particular STT conduction time (rho = −0.75; p<0.010). Correlations between FA and the clinical and electrophysiological measures were higher in the anterior area (where the spinothalamic tracts are located) than in the posterior area of the spinal cord. Conclusions: The data indicate that diffusion tensor imaging with 3D-fibre tracking is a new imaging method suitable for the objective and quantitative anatomical assessment of spinal somatosensory system dysfunction.

Pain sensitivity and tactile spatial acuity are altered in healthy musicians as in chronic pain patients

Extensive training of repetitive and highly skilled movements, as it occurs in professional classical musicians, may lead to changes in tactile sensitivity and corresponding cortical reorganization of somatosensory cortices. It is also known that professional musicians frequently experience musculoskeletal pain and pain-related symptoms during their careers. The present study aimed at understanding the complex interaction between chronic pain and music training with respect to somatosensory processing. For this purpose, tactile thresholds (mechanical detection, grating orientation, two-point discrimination) and subjective ratings to thermal and pressure pain stimuli were assessed in 17 professional musicians with chronic pain, 30 pain-free musicians, 20 non-musicians with chronic pain, and 18 pain-free non-musicians. We found that pain-free musicians displayed greater touch sensitivity (i.e., lower mechanical detection thresholds), lower tactile spatial acuity (i.e., higher grating orientation thresholds) and increased pain sensitivity to pressure and heat compared to pain-free non-musicians. Moreover, we also found that musicians and non-musicians with chronic pain presented lower tactile spatial acuity and increased pain sensitivity to pressure and heat compared to pain-free non-musicians. The significant increment of pain sensitivity together with decreased spatial discrimination in pain-free musicians and the similarity of results found in chronic pain patients, suggests that the extensive training of repetitive and highly skilled movements in classical musicians could be considered as a risk factor for developing chronic pain, probably due to use-dependent plastic changes elicited in somatosensory pathways.

Automated single-trial assessment of laser-evoked potentials as an objective functional diagnostic tool for the nociceptive system

OBJECTIVE To assess the clinical usefulness of an automated analysis of event-related potentials (ERPs). METHODS Nociceptive laser-evoked potentials (LEPs) and non-nociceptive somatosensory electrically-evoked potentials (SEPs) were recorded in 37 patients with syringomyelia and 21 controls. LEP and SEP peak amplitudes and latencies were estimated using a single-trial automated approach based on time-frequency wavelet filtering and multiple linear regression, as well as a conventional approach based on visual inspection. RESULTS The amplitudes and latencies of normal and abnormal LEP and SEP peaks were identified reliably using both approaches, with similar sensitivity and specificity. Because the automated approach provided an unbiased solution to account for average waveforms where no ERP could be identified visually, it revealed significant differences between patients and controls that were not revealed using the visual approach. CONCLUSION The automated analysis of ERPs characterized reliably and objectively LEP and SEP waveforms in patients. SIGNIFICANCE The automated single-trial analysis can be used to characterize normal and abnormal ERPs with a similar sensitivity and specificity as visual inspection. While this does not justify its use in a routine clinical setting, the technique could be useful to avoid observer-dependent biases in clinical research.

Human primary somatosensory cortex is differentially involved in vibrotaction and nociception

The role of the primary somatosensory cortex (S1) in vibrotaction is well established. In contrast, its involvement in nociception is still debated. Here we test whether S1 is similarly involved in the processing of nonnociceptive and nociceptive somatosensory input in humans by comparing the aftereffects of high-definition transcranial direct current stimulation (HD-tDCS) of S1 on the event-related potentials (ERPs) elicited by nonnociceptive and nociceptive somatosensory stimuli delivered to the ipsilateral and contralateral hands. Cathodal HD-tDCS significantly affected the responses to nonnociceptive somatosensory stimuli delivered to the contralateral hand: both early-latency ERPs from within S1 (N20 wave elicited by transcutaneous electrical stimulation of median nerve) and late-latency ERPs elicited outside S1 (N120 wave elicited by short-lasting mechanical vibrations delivered to index fingertip, thought to originate from bilateral operculo-insular and cingulate cortices). These results support the notion that S1 constitutes an obligatory relay for the cortical processing of nonnociceptive tactile input originating from the contralateral hemibody. Contrasting with this asymmetric effect of HD-tDCS on the responses to nonnociceptive somatosensory input, HD-tDCS over the sensorimotor cortex led to a bilateral and symmetric reduction of the magnitude of the N240 wave of nociceptive laser-evoked potentials elicited by stimulation of the hand dorsum. Taken together, our results demonstrate in humans a differential involvement of S1 in vibrotaction and nociception.NEW & NOTEWORTHY Whereas the role of the primary somatosensory cortex (S1) in vibrotaction is well established, its involvement in nociception remains strongly debated. By assessing, in healthy volunteers, the effect of high-definition transcranial direct current stimulation over S1, we demonstrate a differential involvement of S1 in vibrotaction and nociception.

Reduction of Pain Sensitivity after Somatosensory Therapy in Children with Autism Spectrum Disorders

Children with autism spectrum disorders (ASD) often present with somatosensory dysfunction including an abnormal reactivity to tactile stimuli and altered pain perception. A therapy based on somatosensory stimuli has shown effectiveness in reducing pain sensitivity among adults with cerebral palsy. The present study aims at exploring the influence of somatosensory therapy on somatosensory parameters in children with ASD. Children with high-functioning ASD were randomly assigned to either the intervention (n = 29) or the control group (n = 30). The intervention group received a somatosensory therapy consisting of four types of exercises (touch, proprioception, vibration, stereognosis). Somatosensory function (pressure pain thresholds, tactile thresholds, stereognosis, proprioception) was assessed before and immediately after the therapy. Children in the intervention group showed a significant reduction of pain sensitivity and increase of tactile sensitivity after treatment, whereas children in the control group displayed increased pain sensitivity in the absence of changes of tactile sensitivity. No changes were observed for proprioception or stereognosis. The repetitive somatosensory stimulation therapy led to a decrease of pain sensitivity and an increase of tactile sensitivity. These findings may have important research and clinical implications, as promoting early tactile interventions in children with ASD may lead to a more adequate development of somatosensory processing and less somatosensory abnormalities upon adult life.

Use of prism adaptation in children with unilateral brain lesion: Is it feasible?

INTRODUCTION Unilateral visuospatial deficits have been observed in children with brain damage. While the effectiveness of prism adaptation for treating unilateral neglect in adult stroke patients has been demonstrated previously, the usefulness of prism adaptation in a pediatric population is still unknown. The present study aims at evaluating the feasibility of prism adaptation in children with unilateral brain lesion and comparing the validity of a game procedure designed for child-friendly paediatric intervention, with the ecological task used for prism adaptation in adult patients. METHODS Twenty-one children with unilateral brain lesion randomly were assigned to a prism group wearing prismatic glasses, or a control group wearing neutral glasses during a bimanual task intervention. All children performed two different bimanual tasks on randomly assigned consecutive days: ecological tasks or game tasks. The efficacy of prism adaptation was measured by assessing its after-effects with visual open loop pointing (visuoproprioceptive test) and subjective straight-ahead pointing (proprioceptive test). RESULTS Game tasks and ecological tasks produced similar after-effects. Prismatic glasses elicited a significant shift of visuospatial coordinates which was not observed in the control group. CONCLUSION Prism adaptation performed with game tasks seems an effective procedure to obtain after-effects in children with unilateral brain lesion. The usefulness of repetitive prism adaptation sessions as a therapeutic intervention in children with visuospatial deficits and/or neglect, should be investigated in future studies.

The Two-Arm Coordination Test: Maturation of Bimanual Coordination in Typically Developing Children and Deficits in Children with Unilateral Cerebral Palsy

ABSTRACT Background: Tools to assess bimanual coordination are scant. We aimed to: 1) provide normative data of maturation of bimanual coordination in tipically developing (TD) children measured by the Two Arm Coordination Test (TACT), and 2) validate the TACT as an instrument to specifically discriminate impairment of bimanual coordination in children with unilateral cerebral palsy (UCP). Procedure: Cross-sectional observational study. 252 TD children and 26 children with UCP performed 8 trials of TACT (following a star pattern with a pointer steered by coordinated movements of both arms). Number of errors and time were combined in a performance index of motor learning.Results: In TD children, bimanual coordination improved with age (F(7,244)=36.888, p<.001). Children with UCP had a poorer bimanual coordination than TD children (all t>24.25, all p<.01). TACT scores were correlated moderately to manual dexterity and manual ability (all r>-.452, all p<.039), showing the capacity of the TACT to provide information on different aspects of hand function. Conclusion: TACT is a valid instrument to assess bimanual coordination.

Development of Visuospatial Attention in Typically Developing Children

The aim of the present study is to investigate the development of visuospatial attention in typically developing children and to propose reference values for children for the following six visuospatial attention tests: star cancellation, Ogden figure, reading test, line bisection, proprioceptive pointing and visuo-proprioceptive pointing. Data of 159 children attending primary or secondary school in the Fédération Wallonie Bruxelles (Belgium) were analyzed. Results showed that the childrens performance on star cancellation, Ogden figure and reading test improved until the age of 13 years, whereas their performance on proprioceptive pointing, visuo-proprioceptive pointing and line bisection was stable with increasing age. These results suggest that the execution of different types of visuospatial attention tasks are not following the same developmental trajectories. This dissociation is strengthened by the lack of correlation observed between tests assessing egocentric and allocentric visuospatial attention, except for the star cancellation test (egocentric) and the Ogden figure copy (ego- and allocentric). Reference values are proposed that may be useful to examine children with clinical disorders of visuospatial attention.