Table 5.
Physiological biomarkers of SCAs
| Biomarker | SCA vs. controls | Presymptomatic SCA vs. controls | Presymptomatic SCA vs. Symptomatic SCA | Comparisons between different SCA subtypes |
|---|---|---|---|---|
| Auditory evoked potential | Reduced suppression of P50 in SCA3 [140] | |||
| BAEP | prolonged absolute III and V latencies and interpeak I–III latency in SCA2 [101] prolonged I and III latency in SCA6 [102] |
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| EEG | ↓ late bereitschaftspotential with dominant (right) hand movements in SCA3 [141] |
|||
| F wave amplitudes of ulnar nerve | ↑ in SCA1, SCA2, SCA3 [106] |
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| MEP | ↑ CMCT in SCA1 [104–106], SCA2 [104], SCA3 [104, 107] |
↓ intracortical facilitation in presymptomatic SCA3 [107] |
↑ CMCT in SCA1 vs. SCA2 [104] ↑ RMT in SCA1 vs. |
|
| ↑ RMT in SCA1 [104–106], SCA3 [104] ↑ amplitude in SCA3 [105] ↓ intracortical facilitation in SCA2 [106], SCA3 [106, 107] ↓ SICI in SCA3 [107] |
↓ SICI in presymptomatic SCA3 [107] |
SCA2 [104] Prolonged latency more commonly seen in SCA1 than SCA2 or SCA3 [103] |
||
| SSEP | Loss of cortical SEP in SCA1, SCA2, and SCA3 [103] Prolonged latency of P40 in SCA2 [101] |
Delayed P40 seen in SCA3 (69%) and SCA2 (23%) but not in SCA1 [103] |
||
| VEP | Prolonged P100 more commonly seen in SCA1 than SCA3 [103] | |||
| VOG | Gaze-evoked nystagmus and dysmetric saccade ↑ in SCA1 [99], SCA3 [99, 100], and SCA6 [99] SWJ/SWO ↑ in SCA3 [99, 100] Downward nystagmus in SCA6 [99] pHSN in SCA6 [99] ↑ VOR latency in SCA3 [98] ↓ VORr, VOR40, VOR60, and VOR80 in SCA3 [98] |
SWJ and impaired smooth pursuit ↑ in presymptomatic SCA3 [100] |
Gaze-evoked nystagmus ↑ in symptomatic SCA3 vs. presymptomatic SCA3 [100] |
BAEP: brainstem auditory evoked potentials; CMCT: central motor conduction time; EEG: electroencephalography; MEPs: motor evoked potentials; pHSN: perverted head shaking nystagmus or vertical nystagmus after horizontal head shaking; RMT: resting motor threshold; SICI: short-interval intracortical inhibition; SSEPs: somatosensory evoked potentials; VOG: video-oculography; VOR: vestibulo-ocular reflex; VOR40, VOR60, and VOR80: the median of the eye and head velocity ratio during 35–45, 55–65, and 75–85 ms after head-turning impulse starts.