Reduced regional cerebral blood flow in SPG4-linked hereditary spastic paraplegia

Proof of principle for the clinical use of a CE-certified automatic imaging analysis tool in rare diseases studying hereditary spastic paraplegia type 4 (SPG4)

Usage of MR imaging biomarkers is limited to experts. Automatic quantitative reports provide access for clinicians to data analysis. Automated data analysis was tested for usability in a small cohort of patients with hereditary spastic paraplegia type 4 (SPG4). We analyzed 3T MRI 3D-T1 datasets of n = 25 SPG4 patients and matched healthy controls using a commercial segmentation tool (AIRAscore structure 2.0.1) and standard VBM. In SPG4 total brain volume was reduced by 27.6 percentiles (p = 0.001) caused mainly by white matter loss (- 30.8th, p < 0.001) and stable total gray matter compared to controls. Brain volume loss occurred in: midbrain (- 41.5th, p = 0.001), pons (- 36.5th, p = 0.02), hippocampus (- 20.9th, p = 0.002), and gray matter of the cingulate gyrus (- 17.0th, p = 0.02). Ventricular volumes increased as indirect measures of atrophy. Group comparisons using percentiles aligned with results from VBM analyses. Quantitative imaging reports proved to work as an easily accessible, fully automatic screening tool for clinicians, even in a small cohort of a rare genetic disorder. We could delineate the involvement of white matter and specify involved brain regions. Group comparisons using percentiles provide comparable results to VBM analysis and are, therefore, a suitable and simple screening tool for all clinicians with and without in-depth knowledge of image processing.

Neuroimaging in hereditary spastic paraplegias: from qualitative cues to precision biomarkers

INTRODUCTION

: Hereditary spastic paraplegias (HSP) include a clinically and genetically heterogeneous group of conditions. Novel imaging modalities have been increasingly applied to HSP cohorts which helps to quantitatively evaluate the integrity of specific anatomical structures and develop monitoring markers for both clinical care and future clinical trials.

AREAS COVERED

: Advances in HSP imaging are systematically reviewed with a focus on cohort sizes, imaging modalities, study design, clinical correlates, methodological approaches, and key findings.

EXPERT OPINION

: A wide range of imaging techniques have been recently applied to HSP cohorts. Common shortcomings of existing studies include the evaluation of genetically unconfirmed or admixed cohorts, limited sample sizes, unimodal imaging approaches, lack of postmortem validation, and a limited clinical battery, often exclusively focusing on motor aspects of the condition. A number of innovative methodological approaches have also be identified, such as robust longitudinal study designs, the implementation of multimodal imaging protocols, complementary cognitive assessments, and the comparison of HSP cohorts to MND cohorts. Collaborative multicentre initiatives may overcome sample limitations, and comprehensive clinical profiling with motor, extrapyramidal, cerebellar, and neuropsychological assessments would permit systematic clinico-radiological correlations. Academic achievements in HSP imaging have the potential to be developed into viable clinical applications to expedite the diagnosis and monitor disease progression.

Frontotemporal Pathology in Motor Neuron Disease Phenotypes: Insights From Neuroimaging

Frontotemporal involvement has been extensively investigated in amyotrophic lateral sclerosis (ALS) but remains relatively poorly characterized in other motor neuron disease (MND) phenotypes such as primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), spinal muscular atrophy (SMA), spinal bulbar muscular atrophy (SBMA), post poliomyelitis syndrome (PPS), and hereditary spastic paraplegia (HSP). This review focuses on insights from structural, metabolic, and functional neuroimaging studies that have advanced our understanding of extra-motor disease burden in these phenotypes. The imaging literature is limited in the majority of these conditions and frontotemporal involvement has been primarily evaluated by neuropsychology and post mortem studies. Existing imaging studies reveal that frontotemporal degeneration can be readily detected in ALS and PLS, varying degree of frontotemporal pathology may be captured in PMA, SBMA, and HSP, SMA exhibits cerebral involvement without regional predilection, and there is limited evidence for cerebral changes in PPS. Our review confirms the heterogeneity extra-motor pathology across the spectrum of MNDs and highlights the role of neuroimaging in characterizing anatomical patterns of disease burden in vivo. Despite the contribution of neuroimaging to MND research, sample size limitations, inclusion bias, attrition rates in longitudinal studies, and methodological constraints need to be carefully considered. Frontotemporal involvement is a quintessential clinical facet of MND which has important implications for screening practices, individualized management strategies, participation in clinical trials, caregiver burden, and resource allocation. The academic relevance of imaging frontotemporal pathology in MND spans from the identification of genetic variants, through the ascertainment of presymptomatic changes to the design of future epidemiology studies.

Thalamic atrophy in patients with pure hereditary spastic paraplegia type 4

SPG4 is an autosomal dominant pure form of hereditary spastic paraplegia (HSP) caused by mutations in the SPAST gene. HSP is considered an upper motor neuron disorder characterized by progressive spasticity and weakness of the lower limbs caused by degeneration of the corticospinal tract. In other neurodegenerative motor disorders, the thalamus and basal ganglia are affected, with a considerable impact on disease progression. However, only a few works have studied these brain structures in HSP, mainly in complex forms of this disease. Our research aims to detect potential alterations in the volume and shape of the thalamus and various basal ganglia structures by comparing 12 patients with pure HSP and 18 healthy controls. We used two neuroimaging procedures: automated segmentation of the subcortical structures (thalamus, hippocampus, caudate nucleus, globus pallidus, and putamen) in native space and shape analysis of the structures. We found a significant reduction in thalamic volume bilaterally, as well as an inward deformation, mainly in the sensory-motor thalamic regions in patients with pure HSP and a mutation in SPG4. We also observed a significant negative correlation between the shape of the thalamus and clinical scores (the Spastic Paraplegia Rating Scale score and disease duration). Moreover, we found a 'Group × Age' interaction that was closely related to the severity of the disease. No differences in volume or in shape were found in the remaining subcortical structures studied. Our results suggest that changes in structure of the thalamus could be an imaging biomarker of disease progression in pHSP.

Cortical Damage Associated With Cognitive and Motor Impairment in Hereditary Spastic Paraplegia: Evidence of a Novel SPAST Mutation

To determine the cortical mechanism that underlies the cognitive impairment and motor disability in hereditary spastic paraplegia (HSP), nine HSP patients from a Chinese family were examined using clinical evaluation, cognitive screening, and genetic testing. Controls were matched healthy subjects. White-matter fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD; tract-based spatial statistics), cortical thickness (FreeSurfer), and subcortical gray matter (FIRST) based on T1-weighted MRI and diffusion tensor imaging were analyzed. A novel mutation in the SPAST gene (NM_014946.3, c.1321+2T>C) was detected. Patients had motor disability and low Montreal Cognitive Assessment (MoCA) scores. Patients showed significantly decreased total gray- and white-matter volumes, corpus callosum volume, cortical thickness, and subcortical gray-matter volume as well as significantly lower FA and AD values and significantly higher MD and RD values in the corpus callosum and corticospinal tract. Cortical thickness, subcortical gray-matter volume, and MoCA score were negatively correlated with disease duration. Cortical thickness in the right inferior frontal cortex was negatively correlated with Spastic Paraplegia Rating Scale score. Cortical thickness and right hippocampus volume were positively correlated with the MoCA score and subscores. In conclusion, brain damage is not restricted to the white matter in SPG4-HSP patients, and widespread gray-matter damage may account for the disease progression, cognitive impairment, and disease severity in SPG4-HSP.

Neuroimaging in Hereditary Spastic Paraplegias: Current Use and Future Perspectives

Hereditary spastic paraplegias (HSP) are a large group of genetic diseases characterized by progressive degeneration of the long tracts of the spinal cord, namely the corticospinal tracts and dorsal columns. Genotypic and phenotypic heterogeneity is a hallmark of this group of diseases, which makes proper diagnosis and management often challenging. In this scenario, magnetic resonance imaging (MRI) emerges as a valuable tool to assist in the exclusion of mimicking disorders and in the detailed phenotypic characterization. Some neuroradiological signs have been reported in specific subtypes of HSP and are therefore helpful to guide genetic testing/interpretation. In addition, advanced MRI techniques enable detection of subtle structural abnormalities not visible on routine scans in the spinal cord and brain of subjects with HSP. In particular, quantitative spinal cord morphometry and diffusion tensor imaging look promising tools to uncover the pathophysiology and to track progression of these diseases. In the current review article, we discuss the current use and future perspectives of MRI in the context of HSP.

Resting state fMRI studies in SPG4-linked hereditary spastic paraplegia

OBJECTIVE

The study aimed to investigate the functional alterations of spontaneous brain activity in patients with spastic paraplegia type 4 (SPG4), and the relationship with the severity of spasticity.

METHODS

Twelve patients with SPG4 and ten healthy controls underwent resting-state functional magnetic resonance imaging (rs-fMRI). Amplitude of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo) were used to characterize regional neural function, and functional connectivity (FC) was used to evaluate the functional integration of the brain network.

RESULTS

Compared to healthy controls, patients with SPG4 exhibited significantly decreased ReHo values in the medial superior frontal gyrus. ALFF values were lower in left insula and higher in right precentral and superior frontal gyrus of the patient group. Increased ALFF values in the right precentral gyrus negatively correlated with Spastic Paraplegia Rating Scale (SPRS) scores in the patients. The connectivity study showed that the SPG4 patients had one increased FC between the left middle frontal gyrus to the left middle orbitofrontal gyrus, and pairs of decreased FC.

CONCLUSIONS

Our findings confirm that the baseline regional neural activity and interregional connectivity are altered in many brain regions in patients with SPG4, and certain changes are correlated with disease severity, providing potential diagnostic markers for SPG4.

Cognitive Impairment Involving Social Cognition in SPG4 Hereditary Spastic Paraplegia

Objectives. To describe cognitive assessment including social cognition in SPG4 patients. Methods. We reported a series of nine patients with SPG4 mutation with an extensive neuropsychological examination including social cognition assessment. Results. None of our patients presented with mental retardation or dementia. All presented with mild cognitive impairment with a high frequency of attention deficit (100%), executive disorders (89%), and social cognition impairment (78%). An asymptomatic patient for motor skills presented with the same cognitive profile. No correlation was found in this small sample between cognitive impairment and motor impairment, age at disease onset, or disease duration. Conclusions. SPG4 phenotypes share some cognitive features of frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Cognitive disorders including executive disorders and social cognition impairment are frequent in SPG4 patients and might sometimes occur before motor disorders. Therefore, cognitive functions including social cognition should be systematically assessed in order to improve the clinical management of this population.

Gray and white matter alterations in hereditary spastic paraplegia type SPG4 and clinical correlations

Hereditary spastic paraplegias (HSP) are a group of clinically and genetically heterogeneous disorders with the hallmark of progressive spastic gait disturbance. We used advanced neuroimaging to identify brain regions involved in SPG4, the most common HSP genotype. Additionally, we analyzed correlations between imaging and clinical findings. We performed 3T MRI scans including isotropic high-resolution 3D T1, T2-FLAIR, and DTI sequences in 15 adult patients with genetically confirmed SPG4 and 15 age- and sex-matched healthy controls. Brain volume loss of gray and white matter was evaluated through voxel-based morphometry (VBM) for supra- and infratentorial regions separately. DTI maps of axial diffusivity (AD), radial diffusivity (RD), mean diffusivity (MD), fractional anisotropy (FA), and measured anisotropy (MA1) were analyzed through tract-based special statistics (TBSS). VBM and TBSS revealed a widespread affection of gray and white matter in SPG4 including the corpus callosum, medio-dorsal thalamus, parieto-occipital regions, upper brainstem, cerebellum, and corticospinal tract. Significant correlations with correlation coefficients r > 0.6 between clinical data and DTI findings could be demonstrated for disease duration and disease severity as assessed by the spastic paraplegia rating scale for the pontine crossing tract (AD) and the corpus callosum (RD and FA). Imaging also provided evidence that SPG4 underlies a primarily axonal rather than demyelinating damage in accordance with post-mortem data. DTI is an attractive tool to assess subclinical affection in SPG4. The correlation of imaging findings with disease duration and severity suggests AD, RD, and FA as potential progression markers in interventional studies.

Hereditary spastic paraplegia is not associated with C9ORF72 repeat expansions in a Danish cohort

OBJECTIVES

Hereditary spastic paraplegia (HSP) is a heterogeneous group of neurodegenerative disorders characterized by a progressive gait disorder, lower limb spasticity, hyper-reflexia, weakness and extensor plantar responses. Recently, large intronic hexanucleotide repeat expansions (GGGGCC) in C9ORF72 have been found to cause frontotemporal dementia (FTD), amyotrophic lateral sclerosis and FTD with motor neuron disease. Owing to the overlapping phenotypes among HSP, amyotrophic lateral sclerosis and FTD with motor neuron disease along with shared pathological findings, we hypothesized that C9ORF72 expansions might be a genetic risk factor or modifier of HSP.

METHODS

Clinically characterized HSP patients were investigated for elongations in the hexanucleotide repeat of C9ORF72.

RESULTS

Upon analyses of the repeat lengths in the C9ORF72 gene in a Danish cohort of HSP patients, we found no expansions.

CONCLUSION

We conclude that HSP is most likely not associated with repeat expansions in C9ORF72.

Diffusion tensor imaging in SPG11- and SPG4-linked hereditary spastic paraplegia

The aim of this study was to identify potential diagnostic markers of Hereditary Spastic Paraplegia (HSP). We investigated the white matter features of spastic gait (SPG)11- and SPG4-linked HSP, using diffusion tensor imaging performed with a 3-Tesla (3T) scanner. We examined four patients with SPG11 mutations, three with SPG4 mutations, and 26 healthy controls. We obtained maps of fractional anisotropy (FA) and mean diffusivity (MD), which we analyzed through both region of interest -based approach and tract-based spatial statistics (TBSS). Compared with healthy controls, SPG11 patients presented increased MD and decreased FA in the semioval centers, frontal and peritrigonal white matter, posterior limb of the internal capsule, and throughout the corpus callosum. Similar alterations were seen in the SPG4 patients at the levels of the semioval centers, the posterior limb of the internal capsule, the left cerebral pedicle, the genu and trunk of the corpus callosum, and the peritrigonal white matter on the left. No MD or FA alterations were observed in the cerebellar white matter. In a direct comparison, white matter alterations were more pronounced and widespread in HSP-SPG11 than in HSP-SPG4 patients. Joint TBSS analysis of all three groups confirmed significant widespread alterations of FA and MD values in the supratentorial white matter. This noninvasive study documented the presence of altered diffusivity in white matter in both forms of HSP, which could represent an important diagnostic marker of HSP. The association of reduced FA and increased MD in this patient population supports the interpretation of HPG as a neurodegenerative disorder.

SPG3A-linked hereditary spastic paraplegia associated with cerebral glucose hypometabolism

SPG3A-linked hereditary spastic paraplegia (HSP) is a rare autosomal dominant motor disorder caused by a mutation in the SPG3A gene, and is characterized by progressive motor weakness and spasticity in the lower limbs, without any other neurological abnormalities. SPG3A-linked HSP caused by a R239C mutation has been reported to present a pure phenotype confined to impairment of the corticospinal tract. However, there is still a debate about the etiology of this motor deficit with regard to whether it is peripheral or central. We herein report two patients who were heterozygous for a R239C mutation in the SPG3A gene. Two middle-aged Japanese sisters had been suffering from a pure phenotype of HSP since their childhood. Both patients had a significant decrease in glucose metabolism in the frontal cortex medially and dorsolaterally in a [(18)F]-fluorodeoxyglucose (FDG) positron emission photography (PET) study and low scores on the Frontal Assessment Battery. A real-time PCR analysis in normal subjects showed the frontal cortex to be the major location where SPG3A mRNA is expressed. The present finding that the frontal glucose hypometabolism was associated with frontal cognitive impairment indicates that widespread neuropathology associated with mutations in the SPG3A gene may be present more centrally than previously assumed.

Functional MRI of the cortical sensorimotor system in patients with hereditary spastic paraplegia

OBJECTIVES

The study aimed to use functional magnetic resonance imaging to ascertain changes in sensorimotor system function in patients with hereditary spastic paraplegia and to correlate it with severity of spasticity and paresis.

SETTING

Tartu University Hospital, Tartu, Estonia.

METHODS

Nine patients with autosomal-dominant pure HSP and 14 age- and sex-matched healthy controls were investigated with a 1.5T fMRI scanner during flexion/extension of the right-hand fingers and right ankle. Images were analysed with a general linear model and Statistical Parametrical Mapping software. Highest Z-scores were identified from probability maps, and weighted laterality indices were calculated using combined bootstrap/histogram analysis; these were correlated with clinical severity of spasticity and paresis.

RESULTS

During hand movements, clusters located in contralateral primary sensorimotor and premotor areas activated in both controls and patients. Bilateral activation occurred in the supplementary motor area, parietal operculum and cerebellum (predominantly ipsilateral). During the ankle task, bilateral activation was noted in the primary sensorimotor area, supplementary motor area and cerebellum. Activation clusters in HSP patients were smaller than those in controls in the sensorimotor area, especially during the ankle task, and more pronounced ipsilaterally in cerebellum both during hand and ankle motor tasks. Spasticity was significantly associated with contralateral activation in the sensory area and correlated negatively with the highest Z-scores in Brodmann areas 1-2-3 and 4.

CONCLUSION

Our results suggest changes in cortical sensorimotor network function in patients with HSP compared with healthy subjects. Lower activation in patients might reflect damage to the corticospinal tract, be influenced by compensatory mechanisms, and/or be a reflection of neurorehabilitation.

Functional changes of the cortical motor system in hereditary spastic paraparesis

BACKGROUND

Hereditary spastic paraparesis (HSP) is a heterogeneous group of disorders characterized by progressive bilateral lower limb spasticity. Functional imaging studies in patients with corticospinal tract involvement have shown reorganization of motor circuitry. Our study investigates functional changes in sensorimotor brain areas in patients with HSP.

METHODS

Twelve subjects with HSP and 12 healthy subjects were studied. Functional magnetic resonance imaging (fMRI) was used to measure brain activation during right-hand finger tapping. Image analysis was performed using general linear model and regions of interest (ROI)-based approach. Weighted laterality indices (wLI) and anterior/posterior indicies (wAI and wPI) were calculated for predefined ROIs.

RESULTS AND DISCUSSION

Comparing patients and controls at the same finger-tapping rate (1.8 Hz), there was increased fMRI activation in patients' bilateral posterior parietal cortex and left primary sensorimotor cortex. No differences were found when comparing patients and controls at 80% of their individual maximum tapping rates. wLI of the primary sensorimotor cortex was significantly lower in patients. Subjects with HSP also showed a relative increase in the activation of the posterior parietal and premotor areas compared with that of the primary sensorimotor cortex. Our findings demonstrate an altered pattern of cortical activation in subjects with HSP during motor task. The increased activation probably reflects reorganization of the cortical motor system.

Motor activation in SPG4-linked hereditary spastic paraplegia

OBJECTIVE

The aim of this study was to investigate the extent of motor cortical functional reorganisation in patients with SPG4-linked hereditary spastic paraplegia by exploring cortical motor activation related to movements of clinically affected (lower) and unaffected (upper) limbs.

METHODS

Thirteen patients and 13 normal controls matched for age, gender and handedness underwent O15-labelled water positron emission tomography during (1) right ankle flexion-extension, (2) right shoulder flexion-extension and (3) rest. Within-group comparisons of movement vs. rest (simple main effects) and between-group comparisons of movement vs. rest (group x behavioural state interaction) were performed using a random effects approach and statistical parametric mapping (SPM99).

RESULTS

Patterns of motor activation were generally comparable between groups during both tasks, although patients had a tendency towards more widespread activation in sensorimotor cortical and cerebellar regions. Statistically significant differences were restricted to the ankle movement response, however, where patients showed significantly increased regional cerebral blood flow in the right and left primary motor cortices, the supplementary motor areas and the right premotor cortex compared to controls.

CONCLUSIONS

Motor cortical reorganisation may explain this result, but as no significant differences were recognised in the motor response of the unaffected limb, differences in functional demands should also be considered.