Triple stimulation technique in patients with spinocerebellar ataxia type 6.
OBJECTIVE
To establish further evidence that SCA6 may not be a pure cerebellar syndrome.


METHODS
Seven patients with genetically confirmed SCA6 and 9 age-matched normal controls were studied. Recordings of the CMAP were obtained from the right first dorsal interosseus muscle. Transcranial magnetic stimulation of the left motor cortex was applied to the contralateral scalp with a plane figure-of-8 coil. Conventional transcranial magnetic stimulation (TMS), central motor conduction time (CMCT) by F-wave method and the triple stimulation technique (TST) amplitude ratio (TST test/TST control) were investigated.


RESULTS
The mean resting motor threshold and mean CMCT did not show significant differences between normal controls and patients, but the mean TST amplitude ratio was significantly smaller in patients than in controls.


CONCLUSIONS
An abnormal TST represents upper motor neuron loss, central axon lesions or conduction blocks, or inexcitability in response to TMS. The lack of pathological changes in the corticospinal tract of patients with SCA6 indicates that this abnormality may be caused by crossed cerebellar diaschisis, or a functional disorder in the brain resulting from CACNA1A mutations.


CONCLUSIONS
TST is a useful method for quantifying corticospinal tract dysfunction.
Sakuma
Kenji
K
Department of Biological Regulation, Section of Environment and Health Science, School of Health Sciences, Faculty of Medicine, Tottori University, Yonago, Japan. ksakuma@grape.med.tottori-u.ac.jp
Adachi
Yoshiki
Y
Fukuda
Hiroki
H
Kai
Tohru
T
Nakashima
Kenji
K
D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D004056:Differential Threshold; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology; D009431:Neural Conduction; D011930:Reaction Time; D020754:Spinocerebellar Ataxias / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*