Improved Sensation With Transcutaneous Spinal Cord Stimulation Following Chronic Spinal Cord Injury

Following spinal cord injury (SCI), recovery of sensation is often neglected despite its critical roles in motor task execution and injury prevention. The Up-LIFT trial recently found targeted transcutaneous spinal cord stimulation (tSCS) combined with rehabilitation significantly improved sensation in addition to upper extremity (UE) strength and function. Here, we explore the clinical and functional significance of these sensory improvements.

Sixty participants with chronic, incomplete cervical SCI completed a two-month rehabilitation run-in phase followed by two months of tSCS + rehabilitation. At baseline and following each month of therapy, sensation was assessed using the sensory components of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) exam and the Graded Redefined Assessment of Strength, Sensibility, and Prehension (GRASSP). The magnitude, distribution, and meaningfulness of changes in sensory metrics were analyzed. Stepwise linear regression models assessed the relative strengths of relationships between sensation and/or motor abilities with functional outcomes.

Following combined tSCS+rehabilitation, ISNCSCI-Upper Extremity light touch and pin prick scores significantly improved (all p $\le 0.01$ ) with more than 50% of individuals with initial sensory deficits in upper extremity dermatomes demonstrating improvements following tSCS+rehabilitation. Notably, 53% of participants gained new upper extremity sensation following tSCS intervention. In line with these findings, GRASSP palmar sensibility improved across all three fingertip locations (p = 0.006), with both ISNCSCI and GRASSP assessments revealing that the largest improvements occurred at the C8 dermatome. ISNCSCI UE sensory scores correlated moderately with functional assessments (Capabilities of Upper Extremity Test (CUE-T) $\rho =0.57$ ; GRASSP Prehension Performance $\rho =0.51$ ), with stepwise regression models revealing that the inclusion of UE sensation alongside UE motor scores provided better prediction of both functional assessment scores compared to motor scores alone. No improvements were noted following rehabilitation alone.

tSCS + rehabilitation induced widespread and clinically meaningful improvements in sensation across multiple dermatomes. These sensory improvements, together with improved strength, are important for conferring functional gains.