Effect of median-nerve electrical stimulation on bold activity in acute ischemic stroke patients

Introduction: The aim of the work is to investigate the blood oxygenation level dependent activation during somatosensory electrical stimulation of median nerve in acute stroke patients and to define the correlation with ischemic damage (anatomical images) and with the clinical recovery over time. Methods: Fourteen acute stroke patients underwent functional magnetic resonance imaging during contralesional median-nerve electrical stimulation with 3T Magnetic Resonance (MR) scanner (MAGNETOM Allegra, Siemens) from 12 to 48 hours after stroke. A new method to measure the haemodynamic reponse in stroke patients was studied. Diffusion tensor imaging and motor evoked potential by Transcranial magnetic stimulation were also acquired to validate the findings. Different clinical scales as National Institute of Health scale, Barthel index, European Stroke Scale, tactile-thermal scale, and Kinesthetic Sensitivity Test at the time of fMRI recording (t0), one month after stroke (t1), and four-five months after stroke (t2) were measured. Results: Four patients with no fMRI activation during somatosensory stimulation in the early days after stroke had bad clinical recovery after three months, whereas eight patients with a normal activation pattern in primary sensory motor area in acute phase had good clinical recovery. Two patients showed low correlation between bold activation and clinical recovery. TMS and DTI were partially correlated with clinical recovery and fMRI findings. Conclusions: Stimulation of peripheral nerve during the functional magnetic resonance imaging provide important clinical insights on the “functional reserve” in patients affected by stroke with an important prognostic value already in the acute period of cerebrovascular accident.