Position-cortical coherence as a marker for somatosensory integrity early post-stroke, a prospective cohort study

Introduction: Neurophysiological assessments in addition to clinical scales can potentially elucidate the role of somatosensory function in post-stroke motor recovery. Main objective:To investigate the longitudinal construct validity of positioncortical coherence (PCC), the agreement between evoked wrist perturbations and EEG, as a measure of afferent integrity, with respect to longitudinal recovery of sensorimotor function. Methods: PCC was measured serially in 48 patients after a fi rst-ever ischemic stroke, in addition to Fugl-Meyer motor assessment of the upper extremity (FM-UE) and Erasmus modifi cation of the Nottingham Sensory Assessment (EmNSA), within 3, 5, 12 and 26 weeks post-stroke. Change in PCC over time represented by: percentage presence of PCC (%PCC), mean amplitude of PCC over the affected hemisphere (Amp-A) were addressed as well as their association with FM-UE and EmNSA. Patients were classifi ed into: expectedfi tters (FM-UE-baseline=18 points), unexpected-fi tters (FM-UE-baseline<18 points) and non-fi tters (FM-UE-baseline<18 points), to the proportional recovery model. Results and discussion: %PCC increased from baseline to 12 weeks post-stroke (ß:1.6%, CI:0.32-2.86%, P=0.01), which was no longer signifi cant after adjusting for EmNSA and FM-UE. A signifi cant positive association was found between %PCC, Amp-A and EmNSA. Unexpected fi tters (N=8) showed longitudinally signifi cantly higher %PCC than those expected to fi t the proportional recovery model (N=23). Conclusion: We demonstrated the longitudinal construct validity of %PCC and Amp-A as a measure of afferent pathway integrity. A high %PCC in unexpected fi tters suggests that this marker contains information above afferent integrity, i.e. cortical excitability. More work is needed to improve clinical prediction models for functional outcome post-stroke.