Short-latency afferent inhibition and its relationship to covert sensory and motor hand impairment in multiple sclerosis

Abstract

Objective: To investigate sensorimotor integration by quantifying short-latency afferent inhibition (SAI) in people with MS who experience manual dexterity problems compared to controls.

Methods: 22 people with MS with self-reported manual dexterity problems and 10 sex and age-matched controls were assessed using various upper extremity clinical tests. SAI was assessed by a transcranial magnetic stimulation pulse over the primary motor cortex preceded by peripheral nerve stimulation to the median nerve at 6 interstimulus intervals 2 - 8 ms longer than individualized N20 latencies.

Results: Although within normal limits, persons with MS exhibited significantly slower Nine Hole Peg Test performance and pinch strength in the dominant hand. They also exhibited greater sensory impairment (monofilament test) in the dominant hand. Persons with MS showed significantly greater disinhibition of SAI in the dominant hand compared to controls, which was significantly correlated with weaker pinch strength.

Conclusion: Reduced SAI in people with MS, particularly in the dominant hand, signifies disruptions in cortical cholinergic inhibitory activity and is associated with lower pinch strength.

Significance: Evaluating changes in SAI may offer insight into the disrupted cortical cholinergic inhibitory activity that contributes to sensorimotor disintegration, potentially advancing disease management in persons with MS.

Keywords: Dexterity; Multiple Sclerosis; Sensorimotor integration; Short-latency afferent inhibition; TMS; Upper extremity.