P3-2-05. Transcranial magnetic stimulation over the cerebellum facilitates excitability of spinal reflex in spinocerebellar ataxia

We reported that cerebellar transcranial magnetic stimulation (TMS) facilitates spinal reflex in healthy humans. The aim of this study was to investigate whether the “cerebellar” spinal facilitation (CSpF) appears in patients with spinocerebellar ataxia (SCA) with atrophy in the cerebellar cortex and dentate nucleus (DN). Two patients with SCA (one was SCA6 and the other was SCA31), participated in this study. Cerebellar inhibition (CBI) was tested using paired-TMS-paradigm with interstimulus intervals (ISI) of 1–8 ms in the right first dorsal interosseous muscle. To measure CSpF, we delivered TMS over the right cerebellum 100–130 ms before right tibial nerve stimulation, and CSpF was calculated with obtained conditioned/unconditioned H-reflex amplitude in the right soleus muscle. Voxel-based morphometry was used to verify the atrophy in cerebellar cortex and the DN. The results showed absence of CBI, but there was a significant facilitation of the H-reflex which occurred in the 120 ms ISI in both patients. These findings indicate that the pathways associated with the induction of CSpF and CBI are different, and that the cerebellar cortex and the DN are not required for inducing CSpF. Possible generator of CSpF could be other deep cerebellar nuclei or the brain stem.