Relationship between Hemiparetic Upper Limb Motor Function and Median Nerve Somatosensory Evoked Potential among Chronic Stroke Survivors

The afferent input following stroke has an important role in motor relearning. The purpose of this study is to describe the relationship between upper limb clinical motor function and the status of the afferent system among chronic stroke survivors. Twenty-four chronic stroke survivors participated in the study. Clinical motor function of the paretic arm was assessed with the upper extremity portion of the Fugl-Meyer Motor Assessment (FMA). All subjects also underwent somatosensory evoked potential (SSEP) assessments of both median nerves. The FMA total scores were significantly correlated with the amplitudes of SSEPs (r = .68; p = .008). Data suggest a significant relationship between the status of the afferent system and clinical motor function among chronic stroke survivors. Introduction/Background Loss of motor function is a common and devastating outcome of stroke. The recovery from motor deficit from stroke can occur with functional reorganization of sensorimotor cortex. Motor control represents a complex interplay between afferent and efferent systems. Several studies suggest that the afferent system has an important role in both motor learning and motor recovery. The examination of the sensorimotor cortex of proficient Braille readers demonstrated expansion of the motor map of the reading hand, but also of the somatosensory map. An animal study revealed that ablation of a portion of the sensory cortex representing a given digit causes the intact adjacent sensory cortex to begin receiving input from that digit. These findings are consistent with the clinical observation that stroke survivors with only motor impairment experience significantly greater functional recovery than those who have both motor and sensory deficits. The measurement of somatosensory evoked potentials (SSEPs) is a valid and objective method of assessing the integrity of afferent pathway of central nervous system. SSEPs are good predictors of clinical motor recovery following stroke. Abnormal median nerve SSEP studies predict poor upper extremity function during stroke rehabilitation. Pavot et al also showed that SSEP results divided into four grades were significant predictors of functional outcome. Although these earlier studies suggest that SSEP results can be used as prognosticators for future motor recovery, it is unclear whether it can be used as a measure of central neuroplasticity with respect to motor recovery. Prior to utilizing SSEP as an outcome measure for motor recovery, the validity of SSEP reflecting concurrent clinical motor function must be demonstrated. Thus, the purpose of this study is to elucidate the relationship between median nerve SSEP parameters and concurrent clinical motor function of the hemiparetic upper limb among chronic stroke survivors.