Central motor pathways in tropical spastic paraparesis: a combined transcranial magnetic stimulation and diffusion...

Previous transcranial magnetic stimulation (TMS) studies in patients with tropical spastic paraparesis (TSP) have focused on central motor conduction time measurements while other TMS parameters remained unexplored. From a neuroradiological point of view, pyramidal tract involvement with magnetic resonance imaging and diffusion tensor imaging (DTI) has been rarely reported in TSP.  Accordingly, the present study investigated the mean threshold (MT) and silent period (SP) as well as DTI measurements in TSP.

A 35-year-old female patient presented with a 15-year history of spastic paraparesis with minimal upper-limb involvement. Serum and cerebrospinal fluid samples were positive for HTLV-I. TMS was performed with a figure-of-eight coil (recording, abductor hallucis and first dorsal interosseous muscles). Thr was measured at 1 % steps. SPs were elicited at 5 % increments from 0 to 100 % maximum stimulus intensity (SI), and data were used to construct a stimulus/response (S/R) curve of SI vs SP. The resulting S/R curves were fitted to a Boltzmann equation and statistically compared to control data. Voxel-based DTI analysis was performed with SPM 99. Corticospinal tractography was based on diffusion tensor data. The TMS examination disclosed that MT was significantly increased (54.5 ± 6.36 % vs 41.08 ± 7.85 % in a group of 82 controls, p=0.019). The patient's SP S/R curve had significantly reduced Max values compared to 13 age-matched controls (160.4 ± 0.91 ms vs 228.36 ± 38.69 ms, p <0.001). Fractional anisotropy was decreased in a cluster of voxels corresponding to the area of the pyramidal tract (0.388 ± 0.015 vs 0.506 ± 0.02 in 20 age-matched controls, p <0.001).

The described results provide novel neurophysiological and imaging evidence for central motor pathways malfunctioning in TSP. HIPPOKRATIA 2017, 21(4): 191-193.