The role of corticospinal excitability and corticospinal lesion load in recovery of manual dexterity after stroke: A longitudinal pilot study

Abstract

Impaired manual dexterity is frequently reported after stroke and thought to result from corticospinal tract (CST) damage. However, how CST function contributes to functional recovery remains unclear. In this prospective longitudinal study we investigated recovery of dexterity and CST injury and excitability in six patients undergoing conventional rehabilitation. The Finger Force Manipulandum was used to measure dexterity components like force control, finger tapping and independence of finger movements. Transcranial magnetic stimulation was used to measure CST excitability, and structural MRI to calculate weighted-CST lesion load. Clinical tests showed complete recovery of gross motor hand movements in three patients by six months (maximal Fugl–Meyer Upper Extremity assessment score for hand). At six months, four patients had fully recovered in their ability to accurately control finger force. However, tapping speed and independence of finger movements remained affected in all patients at six months when compared to healthy subjects. Recovery in gross motor hand movements and finger force control occurred in those patients with smallest CST lesion load and recovery of CST excitability on TMS, although motor evoked potentials (MEPs) remained of smaller amplitude compared to those evoked from the contralesional side. The two patients with poorest recovery in manual dexterity showed persistent absence of MEPs and greatest structural injury to CST. Although in a small patient sample, the findings show persistent deficits in manual dexterity after stroke despite good recovery of gross motor hand function and partial recovery of CST excitability, suggesting that CST integrity may be necessary but not sufficient for post-stroke recovery of dexterity.