Alterations in cortical excitability and central motor conduction time in spinocerebellar ataxias 1, 2 and 3: a comparative study.

INTRODUCTION

Spinocerebellar ataxias 1, 2 and 3 (SCA1, SCA2 and SCA3) are CAG repeat disorders. The prevalence of changes in the cortical excitability and central motor conduction time (CMCT) in these disorders is largely unknown, and there are few studies which have compared these findings in the subtypes of SCA. The objectives of this study were to measure the cortical resting motor threshold (RMT) and CMCT using transcranial magnetic stimulation in patients with SCA1, SCA2, and SCA3.

METHODS

The subjects of this study were 32 genetically confirmed patients with SCA (SCA1 = 15, SCA2 = 11, SCA3 = 6). Transcranial magnetic stimulation (TMS) was performed using a figure-of-eight coil attached to Magstim 200 stimulator. Motor evoked potentials were recorded from first dorsal interosseous at rest. RMT was determined using standard techniques and the CMCT by 'F' wave method. Comparison was made with data from 32 healthy controls.

RESULTS

Compared to controls, the patients with SCA had significantly higher mean RMT as well as CMCT (RMT: 49.9 ± 9.1 vs. 41.5 ± 6.6, p < 0.0001; CMCT: 7.7 ± 2.3 ms vs. 4.8 ± 0.6 ms; p < 0.0001). When compared separately with the controls, while all the three subtypes of SCAs had significantly prolonged CMCT, only SCA1 and SCA3, but not SCA2 had significantly greater RMT. RMT and CMCT between patients with SCA2 and SCA3, and between SCA1 and SCA3 did not differ significantly, while SCA1 had significantly higher RMT and CMCT than SCA2.

CONCLUSIONS

Patients with SCA have reduced cortical excitability and prolonged central motor conduction time, which was most evident in SCA1 and least in SCA2.