Imaging biomarkers for early multiple system atrophy

Neuroradiological findings in GAA- FGF14 ataxia (SCA27B): more than cerebellar atrophy

Background

GAA- FGF14 ataxia (SCA27B) is a recently reported late-onset ataxia caused by a GAA repeat expansion in intron 1 of the FGF14 gene. Initial studies revealed cerebellar atrophy in 74-97% of patients. A more detailed brain imaging characterization of GAA- FGF14 ataxia is now needed to provide supportive diagnostic features and earlier disease recognition.

Methods

We performed a retrospective review of the brain MRIs of 35 patients (median age at MRI 63 years; range 28-88 years) from Quebec (n=27), Nancy (n=3), Perth (n=3) and Bengaluru (n=2) to assess the presence of atrophy in vermis, cerebellar hemispheres, brainstem, cerebral hemispheres, and corpus callosum, as well as white matter involvement. Following the identification of the superior cerebellar peduncles (SCPs) involvement, we verified its presence in 54 GAA- FGF14 ataxia patients from four independent cohorts (Tübingen n=29; Donostia n=12; Innsbruck n=7; Cantabria n=6). To assess lobular atrophy, we performed quantitative cerebellar segmentation in 5 affected subjects with available 3D T1-weighted images and matched controls.

Results

Cerebellar atrophy was documented in 33 subjects (94.3%). We observed SCP involvement in 22 subjects (62.8%) and confirmed this finding in 30/54 (55.6%) subjects from the validation cohorts. Cerebellar segmentation showed reduced mean volumes of lobules X and IV in the 5 affected individuals.

Conclusions

Cerebellar atrophy is a key feature of GAA- FGF14 ataxia. The frequent SCP involvement observed in different cohorts may facilitate the diagnosis. The predominant involvement of lobule X correlates with the frequently observed downbeat nystagmus.

Quantitative cellular changes in multiple system atrophy brains

Multiple system atrophy (MSA) is a neurodegenerative disorder characterised by a combined symptomatology of parkinsonism, cerebellar ataxia, autonomic failure and corticospinal dysfunction. In brains of MSA patients, the hallmark lesion is the aggregation of misfolded alpha-synuclein in oligodendrocytes. Even though the underlying pathological mechanisms remain poorly understood, the evidence suggests that alpha-synuclein aggregation in oligodendrocytes may contribute to the neurodegeneration seen in MSA. The primary aim of this review is to summarise the published stereological data on the total number of neurons and glial cell subtypes (oligodendrocytes, astrocytes and microglia) and volumes in brains from MSA patients. Thus, we include in this review exclusively the reports of unbiased quantitative data from brain regions including the neocortex, nuclei of the cerebrum, the brainstem and the cerebellum. Furthermore, we compare and discuss the stereological results in the context of imaging findings and MSA symptomatology. In general, the stereological results agree with the common neuropathological findings of neurodegeneration and gliosis in brains from MSA patients and support a major loss of nigrostriatal neurons in MSA patients with predominant parkinsonism (MSA-P), as well as olivopontocerebellar atrophy in MSA patients with predominant cerebellar ataxia (MSA-C). Surprisingly, the reports indicate only a minor loss of oligodendrocytes in sub-cortical regions of the cerebrum (glial cells not studied in the cerebellum) and negligible changes in brain volumes. In the past decades, the use of stereological methods has provided a vast amount of accurate information on cell numbers and volumes in the brains of MSA patients. Combining different techniques such as stereology and diagnostic imaging (e.g. MRI, PET and SPECT) with clinical data allows for a more detailed interdisciplinary understanding of the disease and illuminates the relationship between neuropathological changes and MSA symptomatology.

Combined regional T1w/T2w ratio and voxel-based morphometry in multiple system atrophy: A follow-up study

Several MRI techniques have become available to support the early diagnosis of multiple system atrophy (MSA), but few longitudinal studies on both MSA variants have been performed, and there are no established MRI markers of disease progression. We aimed to characterize longitudinal brain changes in 26 patients with MSA (14 MSA-P and 12 MSA-C) over a 1-year follow-up period in terms of local tissue density and T1w/T2w ratio in a-priori regions, namely, bilateral putamen, cerebellar gray matter (GM), white matter (WM), and substantia nigra (SN). A significant GM density decrease was found in cerebellum and left putamen in the entire group (10.7 and 33.1% variation, respectively) and both MSA subtypes (MSA-C: 15.4 and 33.0% variation; MSA-P: 7.7 and 33.2%) and in right putamen in the entire group (19.8% variation) and patients with MSA-C (20.9% variation). A WM density decrease was found in the entire group (9.3% variation) and both subtypes in cerebellum-brainstem (MSA-C: 18.0% variation; MSA-P: 5% variation). The T1w/T2w ratio increase was found in the cerebellar and left putamen GM (6.6 and 24.9% variation), while a significant T1w/T2w ratio decrease was detected in SN in the entire MSA group (31% variation). We found a more progressive atrophy of the cerebellum in MSA-C with a similar progression of putaminal atrophy in the two variants. T1w/T2w ratio can be further studied as a potential marker of disease progression, possibly reflecting decreased neuronal density or iron accumulation.