Wallerian degeneration of the corticofugal tracts in chronic stroke: a pilot study relating diffusion tensor imaging, transcranial magnetic stimulation, and hand function.

OBJECTIVE: This study tested the hypothesis that degeneration of the corticofugal tracts (CFTs) is related to poor functional outcome in the upper limb after stroke.
METHODS: . The authors used diffusion tensor imaging to determine the degree of white matter integrity of the CFT (FA(AH/UH)) in chronic stroke patients and controls. The functional integrity of the corticospinal pathway was examined using transcranial magnetic stimulation. Recruitment curves and silent period duration were measured. The relationship between FA(AH/UH) and functional outcome of the upper limb was also assessed using a battery of upper limb function tests.
RESULTS: In patients, FA( AH/UH) correlated positively with the slope of recruitment curves (RC(AH/UH)) and grip strength. FA(AH/UH) also correlated negatively with the silent period duration (SP(AH/UH)). According to the FA(AH/UH), patients were also classified into groups with minimal or extensive Wallerian degeneration (WD). Patients with more extensive WD had poorer grip strength, dexterity, and range of movement.
CONCLUSIONS: The authors' results suggest that structural and functional integrity of the CFT is essential to maintain function of the upper limb after stroke.