The main cause of motor weakness is damage to the primary crossed corticospinal tract. Most patients with stroke (80%-90%) have motor symptoms or signs. Hemiparesis with uniform weakness of the arm and leg associated with hemisensory deficit and speech deficit (dysphasia or dysarthria) usually indicates a large supratentorial lesion that involves the middle cerebral artery (MCA). Such patients have more severe weakness than do those with isolated hemiparesis. Crossed brainstem syndromes, well known with eponyms, are characterized by palsy of one of the 12 cranial nerve pairs associated with a contralateral neurological deficit due to involvement of the neurological long tracts (mainly motor or sensory). The integrity of all motor tracts, with the pyramidal tract as the main descending fiber bundle, but also the corticorubrospinal and corticoreticulospinal systems, appears to account for stroke recovery in a recent in vivo diffusion tensor imaging (DTI) study in chronic stroke patients.

Hematopoietic stem cell (HSC) can be either allogeneic (from another person) or autologous (from the recipient). Autologous hematopoietic stem cell transplantation (HSCT) was first suggested by Burt as a form of intense immunesuppressive therapy. HSCT was proposed as a treatment for multiple sclerosis (MS) based on favorable results in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. The toxicity and efficacy of an autologous HSCT is entirely a consequence of the conditioning regimen. Initial HSCT protocols employed aggressive malignancy-specific myeloablative regimens in patients with progressive MS. Unlike autologous HSCT, the immune compartment arising from allogeneic stem cells have a different and presumably more disease-resistant genetic predisposition towards disease recurrence. Both autologous and allogeneic HSCT require a chemotherapy conditioning regimen to suppress or ablate the immune system. HSCT is the only therapy to consistently demonstrate improvement in neurological disability.