An Electrophysiological Study of Visual Processing in Spinocerebellar Ataxia Type 2 (SCA2)

Abstract

Reports of visual functional impairment in spinocerebellar ataxia type 2 (SCA2) have been studied previously using pattern reversal visually evoked potentials (VEPs) with contradictory results. To provide additional evidence to this area, visual functions were studied using VEPs and event-related potentials (ERPs) in a group of ten patients with genetically verified SCA2. The electrophysiological examination included pattern reversal and motion-onset VEPs as well as visually driven oddball ERPs with an evaluation of a target and a pre-attentive response. In six patients, we found abnormal visual/cognitive processing that differed from normal values in latency, but not in the amplitude of the dominant VEP/ERP peaks. Among the VEPs/ERPs used, the motion-onset VEPs exhibited the highest sensitivity and showed a strong Spearman correlation to SCA2 duration (from r = 0.82 to r = 0.90, p < 0.001) and clinical state assessed by Brief Ataxia Rating Scale (from r = 0.71 (p = 0.022) to r = 0.80 (p < 0.001)). None of the VEP/ERP latencies showed a correlation to the triplet repeats of the SCA2 gene. In three patients, we did not find any visual/cognitive pathology, and one subject showed only a single subtle prolongation of the VEP peak. The observed visual/cognitive deficit was related to the subjects' clinical state and the illness duration, but no relationship to the genetic marker of SCA2 was found. From the VEP/ERP types used, the motion-onset VEPs seems to be the most promising candidate for clinical state monitoring rather than a tool for early diagnostic use.

Visual mismatch negativity (vMMN): A review and meta-analysis of studies in psychiatric and neurological disorders

“…Out of 33 reviewed studies 16 evaluated obligatory sensory components beside the vMMN. The sensory processing was disturbed in 13 of them (Bottari et al, 2014;Cleary, Donkers, Evans, & Belger, 2013;Clery et al, 2012;Clery, Roux, et al, 2013;Fisher et al, 2010;Iijima et al, 1996;Kremlacek et al, 2011;Lorenzo-Lopez et al, 2004;Maekawa et al, 2013Maekawa et al, , 2011Stothart et al, 2014Stothart et al, , 2013, whereas deficits only in components related to processing of deviants was observed in two studies only (Tales & Butler, 2006;Urban et al, 2008). The almost ubiquitous impairment of sensory stimulus processing in reviewed studies suggests that vMMN impairment is not necessarily the only candidate marker for impairments of perceptual processes.…”

“…Using a motion-related vMMN paradigm (in which the vMMN was calculated as an integral of the difference between the deviant minus the standard ERP within an interval 100e200 msec after stimulus onset), Kremlacek et al (2011) found generally preserved vMMN in SCA2, but also a positive correlation between the vMMN and age and age at SCA onset and a negative correlation between the vMMN and pathological load (CAG repeats e cytosineeadenineeguanine triplet coding protein ataxin-2). As highlighted by Kremlacek et al (2011), and similarly to studies of vMMN in AD, patient numbers were relatively small; a reflection of how difficult recruitment can be in such populations when rigorous inclusion and exclusion criteria are observed. However, despite these limitations, such studies show proof of concept in that such patients can be tested successfully using typical vMMN paradigms and that there is some evidence of potential abnormality in the vMMN in neurodegenerative disorders.…”

“…This autosomal dominant neurodegenerative disorder is characterized by progressive movement abnormalities and cerebellar atrophy, with the common SCA genotype 2 (SCA2) typically associated with saccadic slowing, tremor and deterioration in attention, short-term memory and executive dysfunction (Kremlacek et al, 2011). SCArelated abnormalities in visual processing lead to the prediction that an abnormal vMMN will also be evident in this disorder.…”

“…Because of missing parameters for the eCd calculation, 6 studies were not included in the meta-analysis (Clery, Andersson, et al, 2013;Iijima et al, 1995;Kremlacek et al, 2011;Maekawa et al, 2011;Tales et al, 2008), therefore we evaluated 27 studies. Considering that 25 studies in Fig.…”

A Comprehensive Review of Spinocerebellar Ataxia Type 2 in Cuba

“…Additionally, these subjects show prolongation of P100 latency of visual evoked potentials [74]. Event-related evoked potentials revealed the prolongation of P300 latencies in 40% of cases with a significant correlation of this variable with the disease duration and clinical affectation [76].…”