Peripheral nerves are pathologically small in cerebellar ataxia neuropathy vestibular areflexia syndrome: a controlled ultrasound study

Nerve Ultrasound Detects Nerve Atrophy in Patients With Ataxia-Telangiectasia: A Pilot Study

INTRODUCTION/AIMS

Ataxia-telangiectasia (A-T) is a genetic multisystem neurodegenerative disorder characterized by cerebellar ataxia, oculocutaneous telangiectasia, extrapyramidal involvement, peripheral sensorimotor neuropathy, immunodeficiency, pulmonary disease, and an increased risk of malignancy that ultimately determines the shortened lifespan in many patients. A-T nerve ultrasonographic characteristics remain underexplored. This pilot study aimed to characterize the ultrasonographic morphology of peripheral nerves in patients with A-T.

METHODS

Ultrasound cross-sectional areas (CSAs) of the median, ulnar, sural, and tibial nerves were obtained from three A-T patients and were compared to reference values. Nerve conduction studies and electromyography were also performed. Given the small sample size and the exploratory nature of this study, formal statistical analyses were not performed, and descriptive statistics were presented for the data.

RESULTS

Nerve CSAs in A-T patients were smaller than in healthy controls at all measurement sites.

DISCUSSION

Nerve ultrasound revealed atrophy in the peripheral nerves of A-T patients. This reduction in nerve size may distinguish A-T and highlights the utility of nerve ultrasound as a non-invasive diagnostic tool for peripheral sensorimotor neuropathy. These findings may have important implications for early detection in clinical practice.

The Role of Neuromuscular Ultrasound in the Diagnosis of Peripheral Neuropathy

The classification of peripheral neuropathies has traditionally been based on etiology, electrodiagnostic findings, or histopathologic features. With the advent of modern imaging, they now can also be characterized based on their varied distribution of imaging findings. We describe the major morphologic patterns of these changes, which include homogeneous enlargement; homogeneous thinning; focal, multifocal, and segmental enlargement; and focal thinning and beading (multifocal thinning). Representative disorders in each of these categories are discussed, along with examples of the more complex imaging manifestations of neuralgic amyotrophy, nerve transection, and hereditary amyloidosis. An appreciation of the diverse morphologic manifestations of neuropathy can help neuromuscular clinicians conduct appropriate imaging studies with ultrasound and, when needed, order suitable investigations with magnetic resonance neurography.

An Updated Canvas of the RFC1-mediated CANVAS (Cerebellar Ataxia, Neuropathy and Vestibular Areflexia Syndrome)

Proliferation of specific nucleotide sequences within the coding and non-coding regions of numerous genes has been implicated in approximately 40 neurodegenerative disorders. Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS), a neurodegenerative disorder, is distinguished by a pathological triad of sensory neuropathy, bilateral vestibular areflexia and cerebellar impairments. It manifests in adults gradually and is autosomal recessive and multi-system ataxia. Predominantly, CANVAS is associated with biallelic AAGGG repeat expansions in intron 2 of the RFC1 gene. Although various motifs have been identified, only a subset induces pathological consequences, by forming stable secondary structures that disrupt gene functions both in vitro and in vivo. The pathogenesis of CANVAS remains a subject of intensive research, yet its precise mechanisms remain elusive. Herein, we aim to comprehensively review the epidemiology, clinical ramifications, molecular mechanisms, genetics, and potential therapeutics in light of the current findings, extending an overview of the most significant research on CANVAS.

Lower limb nerve ultrasound: A four-way comparison of acquired and inherited axonopathy, inherited neuronopathy and healthy controls

INTRODUCTION/AIMS

In a recent study, we showed that nerve ultrasound of the upper limbs could distinguish inherited sensory neuronopathy from inherited axonopathy; surprisingly, no differences were found in the lower limb nerves. In this study, we compared lower limb nerve ultrasound measurements in inherited neuronopathy, inherited axonopathy, and acquired axonopathy.

METHODS

Tibial and sural nerve ultrasound cross-sectional areas (CSAs) of 34 healthy controls were retrospectively compared with those of three patient groups: 17 with cerebellar ataxia with neuronopathy and vestibular areflexia syndrome (CANVAS), 18 with Charcot-Marie-Tooth type 2 (CMT2), and 18 with acquired length-dependent sensorimotor axonal neuropathy, using ANOVA with post-hoc Tukey honestly significance difference (HSD) (significance level set at p < .05).

RESULTS

The nerve CSAs of CANVAS and CMT2 patients were not significantly different. Both the tibial and the sural nerve CSAs were significantly smaller in CANVAS and CMT2 compared with the acquired axonal neuropathy group. Tibial nerve CSAs of CANVAS and CMT2 were significantly smaller than controls. Tibial and sural nerve CSAs of the acquired axonal neuropathy group were also significantly larger than the controls'.

DISCUSSION

Ultrasound of the lower limb nerves distinguished inherited from acquired axonopathy with the nerve size respectively reduced and increased in these two groups. This has potential implication for the differential diagnosis of these diseases in clinical practice.

Nerve ultrasound in CANVAS-spectrum disease: Reduced nerve size distinguishes genetically confirmed CANVAS from other axonal polyneuropathies

BACKGROUND AND AIMS

Ultrasound nerve cross-sectional area (CSA) of patients affected with axonal neuropathy usually shows normal value. Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) seems to represent an exception, showing smaller CSA, but previous reports did not test for biallelic RFC1 gene repeat expansions.

METHODS

We compared nerve CSA from CANVAS patients (tested positive for biallelic RFC1 gene repeat expansions) with the CSA from a group of patients with chronic idiopathic axonal polyneuropathy (CIAP) who tested negative for RFC1 gene repeat expansions, hereditary axonal neuropathy (Charcot-Marie-Tooth type 2, CMT2), and Friedreich ataxia (FRDA).

RESULTS

We enrolled 15 CANVAS patients (eight men, mean age 66.3 ± 11.5 years, mean disease duration 9.3 ± 4.1 years), affected with sensory axonal neuronopathy. Controls consisted of 13 CIAP (mean age 68.5 ± 12.8 years, seven men), seven CMT2 (mean age 47.9 ± 18.1 years, four men), 12 FRDA (mean age 33.7 ± 8.8, five men). Nerve ultrasound was performed at median, ulnar, sciatic, sural, and tibial nerves and brachial plexus, bilaterally. The nerve CSA from CANVAS patients was significantly smaller than the one from the other cohorts at several sites with significant and high accuracy at Receiver-operating characteristic (ROC) curve analyses. RFC1 AAGGG pentanucleotide expansion, disease duration, and disability did not correlate with CSA at any site, after Bonferroni correction.

INTERPRETATION

Decreased sonographic nerve sizes, in arms and legs, in patients with sensory neuropathy and normal motor conduction studies could point to CANVAS-spectrum disease and help guide appropriate genetic testing.

Morphometry of the sural nerve in diabetic neuropathy: a systematic review

PURPOSE

The aim of this systematic review is to evaluate the usefulness of sural nerve ultrasonography in diagnosing diabetes mellitus (DM) and diabetic polyneuropathy (DPN), the latter of which is a common long-term complication for diabetic patients that frequently involves the sural nerve.

METHODOLOGY

A meta-analysis of the cross-sectional areas (CSAs) of sural nerves in healthy individuals and patients with diabetes mellitus based on a total of 32 ultrasonographic-based studies from 2015 to 2023 was performed. Sub-analyses were performed for factors such as geographical location and measurement site.

RESULTS

The meta-analysis showed that the mean CSA of the sural nerve was significantly larger in DM patients with DPN only compared to healthy individuals across all regions and when pooled together. An age-dependent increase in the CSA of healthy sural nerves is apparent when comparing the paediatric population with adults.

CONCLUSION

Sural nerve ultrasonography can distinguish diabetic adults with DPN from healthy adults based on cross-sectional area measurement. Future studies are needed to clarify the relationships between other parameters, such as body metrics and age, with sural nerve CSAs. Cut-offs for DPN likely need to be specific for different geographical regions.

Cranial Nerve Thinning Distinguishes RFC1-Related Disorder from Other Late-Onset Ataxias

BACKGROUND

RFC1-related disorder (RFC1/CANVAS) shares clinical features with other late-onset ataxias, such as spinocerebellar ataxias (SCA) and multiple system atrophy cerebellar type (MSA-C). Thinning of cranial nerves V (CNV) and VIII (CNVIII) has been reported in magnetic resonance imaging (MRI) scans of RFC1/CANVAS, but its specificity remains unclear.

OBJECTIVES

To assess the usefulness of CNV and CNVIII thinning to differentiate RFC1/CANVAS from SCA and MSA-C.

METHODS

Seventeen individuals with RFC1/CANVAS, 57 with SCA (types 2, 3 and 6), 11 with MSA-C and 15 healthy controls were enrolled. The Balanced Fast Field Echo sequence was used for assessment of cranial nerves. Images were reviewed by a neuroradiologist, who classified these nerves as atrophic or normal, and subsequently the CNV was segmented manually by an experienced neurologist. Both assessments were blinded to patient and clinical data. Non-parametric tests were used to assess between-group comparisons.

RESULTS

Atrophy of CNV and CNVIII, both alone and in combination, was significantly more frequent in the RFC1/CANVAS group than in healthy controls and all other ataxia groups. Atrophy of CNV had the highest sensitivity (82%) and combined CNV and CNVIII atrophy had the best specificity (92%) for diagnosing RFC1/CANVAS. In the quantitative analyses, CNV was significantly thinner in the RFC1/CANVAS group relative to all other groups. The cutoff CNV diameter that best identified RFC1/CANVAS was ≤2.2 mm (AUC = 0.91; sensitivity 88.2%, specificity 95.6%).

CONCLUSION

MRI evaluation of CNV and CNVIII using a dedicated sequence is an easy-to-use tool that helps to distinguish RFC1/CANVAS from SCA and MSA-C.

Neuromuscular ultrasound as a marker for inherited sensory neuronopathy

A review and detailed analysis of the literature over the past two decades has revealed a unique ultrasound feature of pathologically "small" nerves in inherited sensory neuronopathies. Although sample sizes were limited, due to the rarity of these diseases, this characteristic ultrasound finding has been consistently reported across a variety of inherited diseases that affect the dorsal root ganglia. Direct comparisons with both acquired and inherited diseases that primarily affect the axons in the peripheral nerves showed that the ultrasound finding of abnormally "small" cross-sectional areas (CSAs) in mixed nerves of the upper limbs has a high diagnostic accuracy for inherited sensory neuronopathy. Based on this review, ultrasound CSA of the mixed upper limb nerves can be proposed as a marker for inherited sensory neuronopathy.

Sonographic reference values for median nerve cross-sectional area: A meta-analysis of data from healthy individuals

Objective

Establish median nerve CSA reference values and identify patient-level factors impacting diagnostic thresholds.

Methods

Studies were identified through a robust search of multiple databases, and quality assessment was conducted using a modified version of the National Institute of Health Study Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. A meta-analysis was performed to identify normative values stratified by anatomic location. A meta-regression was conducted to examine heterogeneity effects of age, sex, and laterality.

Results

The meta-analysis included 73 studies; 41 (56.2%) were high quality. The median nerve CSA [95% CI] was 6.46mm2 [6.09-6.84], 8.68mm2 [8.22-9.13], and 8.60mm2 [8.23-8.97] at the proximal forearm, the carpal tunnel inlet, and the proximal carpal tunnel, respectively. Age was positively associated with CSA at the level of proximal carpal tunnel (β=0.03mm2, p=0.047). Men (9.42mm2, [8.06-10.78]) had statistically larger proximal tunnel CSA (p = 0.03) as compared to women (7.71mm2, [7.01-8.42]). No difference was noted in laterality.

Conclusion

A reference value for median nerve CSA in the carpal tunnel is 8.60mm2. Adjustments may be required in pediatrics or older adults. The diagnostic threshold of 10.0mm2 for male patients should be cautiously applied as the upper limit of normative averages surpasses this threshold.

Sonographic peripheral nerve cross-sectional area in adults, excluding median and ulnar nerves: A systematic review and meta-analysis

INTRODUCTION/AIMS

Although electromyography remains the "gold standard" for assessing and diagnosing peripheral nerve disorders, ultrasound has emerged as a useful adjunct, providing valuable anatomic information. The objective of this study was to conduct a systematic review and meta-analysis evaluating the normative sonographic values for adult peripheral nerve cross-sectional area (CSA).

METHODS

Medline and Cochrane Library databases were systematically searched for healthy adult peripheral nerve CSA, excluding the median and ulnar nerves. Data were meta-analyzed, using a random-effects model, to calculate the mean nerve CSA and its 95% confidence interval (CI) for each nerve at a specific anatomical location (= group).

RESULTS

Thirty groups were identified and meta-analyzed, which comprised 16 from the upper extremity and 15 from the lower extremity. The tibial nerve (n = 2916 nerves) was reported most commonly, followed by the common fibular nerve (n = 2580 nerves) and the radial nerve (n = 2326 nerves). Means and 95% confidence interval (CIs) of nerve CSA for the largest number of combined nerves were: radial nerve assessed at the spiral groove (n = 1810; mean, 5.14 mm2 ; 95% CI, 4.33 to 5.96); common fibular nerve assessed at the fibular head (n = 1460; mean, 10.18 mm2 ; 95% CI, 8.91 to 11.45); and common fibular nerve assessed at the popliteal fossa (n = 1120; mean, 12.90 mm2 ; 95% CI, 9.12 to 16.68). Publication bias was suspected, but its influence on the results was minimal.

DISCUSSION

Two hundred thirty mean CSAs from 15 857 adult nerves are included in the meta-analysis. These are further categorized into 30 groups, based on anatomical location, providing a comprehensive reference for the clinician and researcher investigating adult peripheral nerve anatomy.

Spinal cord lesion mimicking a dysimmune myelitis revealing CANVAS syndrome

CONTEXT

Posterior spinal cord lesions are found in patients with ganglionopathy. These are normally found in later stages of the neuronopathy as a consequence of dorsal root ganglia degeneration. Cerebellar Ataxia, Neuropathy, Vestibular Areflexia Syndrome (CANVAS) is an emerging neurological disorder. Myelitis lesions have been described in confirmed CANVAS cases.

FINDINGS

We describe a case of a 68-year-old woman with slowly progressive ataxia with paresthesia. Laboratory tests were normal. Total spine MRI showed a C4 posterior spinal cord lesion. Lumbar puncture was positive for oligoclonal bands with normal IgG index and protein level. Paraneoplastic antibodies were not detected. Electromyography showed nonlength dependent sensory neuropathy. The patient was treated with intravenous immunoglobulin for suspected dysimmune myelitis. Over 6 years, she progressively developed other neurological manifestations evoking CANVAS. Nerve conduction study showed isolated sensory impairment over the years and peripheral nerve ultrasound revealed abnormally small nerves. Further genetic testing confirmed the diagnosis.

CONCLUSION

This is the first case of CANVAS syndrome presenting initially with an isolated spinal cord lesion mimicking dysimmune myelitis. The purpose of this case report is to add to the current literature about this evolving neurological syndrome and to aid clinicians in their diagnostic approach in clinical practice.

Ultrasound of peripheral nerves distinguishes inherited sensory neuronopathy of cerebellar ataxia with neuropathy and vestibular areflexia syndrome from inherited axonopathy

Introduction/Aims Recent studies have shown that ultrasound of peripheral nerves can distinguish inherited sensory neuronopathy from acquired axonopathy with a high degree of accuracy. In this study we aimed to determine whether ultrasound can also distinguish inherited sensory neuronopathy from inherited axonopathy. Methods We compared the ultrasound cross-sectional areas (CSAs) of the median, ulnar, sural, and tibial nerves of retrospectively recruited patients with cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS), in whom sensory neuronopathy is a cardinal feature, with Charcot-Marie-Tooth type 2 (CMT2) disease patients, who have an inherited axonopathy, using the Kruskal-Wallis test and receiver-operating characteristic curves. Results There were 17 patients with CANVAS and 18 with CMT2. The upper limb nerve CSAs were significantly smaller in CANVAS than in CMT2 (P < .001), with the CSAs of the median nerve at mid-forearm and ulnar nerve at mid-arm being a third or less the size of those of the CMT2 patients. Nerve ultrasound reliably distinguished CANVAS from CMT2 with ROC areas under the curve between 0.97 and 0.99. The lower limb CSAs of the two patient groups were not significantly different. Discussion Ultrasound of the upper limb nerves distinguishes CANVAS sensory neuronopathy from inherited axonopathy with high accuracy and can therefore be proposed as a reliable additional tool in the investigation of these diseases.

A systematic review: normative reference values of the median nerve cross-sectional area using ultrasonography in healthy individuals

Median nerve cross-sectional area (CSA) was used for screening and diagnosis of neuropathy, but few studies have suggested reference range. Hence, this systematic review was performed to evaluate a normative values of median nerve CSA at various landmarks of upper limb based on ultrasonography. PubMed and Web of science were used to search relevant articles from 2000 to 2020. Forty-one eligible articles (2504 nerves) were included to access median nerve CSA at different landmarks (mid-arm, elbow, mid-forearm, carpal tunnel (CT) inlet and CT outlet). Data was also stratified based on age, sex, ethnicity, geographical location, and method of measurement. Random effects model was used to calculate pooled weighted mean (95% confidence interval (CI), [upper bound, lower bound]) at mid-arm, elbow, mid-forearm, CT inlet and outlet which found to be 8.81 mm², CI [8.10, 9.52]; 8.57 mm² [8.00, 9.14]; 7.07 mm² [6.41, 7.73]; 8.74 mm² [8.45, 9.03] and 9.02 mm² [8.08, 9.95] respectively. Median nerve CSA varies with age, geographical location, and sex at all landmarks. A low (I² < 25%) to considerable heterogeneity (I² > 75%) was observed, indicating the variation among the included studies. These findings show that median nerve CSA is varying not only along its course but also in other sub-variables.

Mechanistic and Therapeutic Insights into Ataxic Disorders with Pentanucleotide Expansions

Pentanucleotide expansion diseases constitute a special class of neurodegeneration. The repeat expansions occur in non-coding regions, have likely arisen from Alu elements, and often result in autosomal dominant or recessive phenotypes with underlying cerebellar neuropathology. When transcribed (potentially bidirectionally), the expanded RNA forms complex secondary and tertiary structures that can give rise to RNA-mediated toxicity, including protein sequestration, pentapeptide synthesis, and mRNA dysregulation. Since several of these diseases have recently been discovered, our understanding of their pathological mechanisms is limited, and their therapeutic interventions underexplored. This review aims to highlight new in vitro and in vivo insights into these incurable diseases.

Recessive cerebellar and afferent ataxias - clinical challenges and future directions

Cerebellar and afferent ataxias present with a characteristic gait disorder that reflects cerebellar motor dysfunction and sensory loss. These disorders are a diagnostic challenge for clinicians because of the large number of acquired and inherited diseases that cause cerebellar and sensory neuron damage. Among such conditions that are recessively inherited, Friedreich ataxia and RFC1-associated cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) include the characteristic clinical, neuropathological and imaging features of ganglionopathies, a distinctive non-length-dependent type of sensory involvement. In this Review, we discuss the typical and atypical phenotypes of Friedreich ataxia and CANVAS, along with the features of other recessive ataxias that present with a ganglionopathy or polyneuropathy, with an emphasis on recently described clinical features, natural history and genotype-phenotype correlations. We review the main developments in understanding the complex pathology that affects the sensory neurons and cerebellum, which seem to be most vulnerable to disorders that affect mitochondrial function and DNA repair mechanisms. Finally, we discuss disease-modifying therapeutic advances in Friedreich ataxia, highlighting the most promising candidate molecules and lessons learned from previous clinical trials.

Nerve ultrasound detects abnormally small nerves in patients with Spinal and Bulbar Muscular Atrophy

Nerve ultrasound detects abnormally small nerves in patients with Spinal and Bulbar Muscular Atrophy.

Review Article "Spotlight on Ultrasonography in the Diagnosis of Peripheral Nerve Disease: The Evidence to Date"

Neuromuscular ultrasound is rapidly becoming incorporated into clinical practice as a standard tool in the assessment of peripheral nerve diseases. Ultrasound complements clinical phenotyping and electrodiagnostic evaluation, providing critical structural anatomical information to enhance diagnosis and identify structural pathology. This review article examines the evidence supporting neuromuscular ultrasound in the diagnosis of compressive mononeuropathies, traumatic nerve injury, generalised peripheral neuropathy and motor neuron disease. Extending the sonographic evaluation of nerves beyond simple morphological measurements has the potential to improve diagnostics in peripheral neuropathy, as well as advancing the understanding of pathological mechanisms, which in turn will promote precise therapies and improve therapeutic outcomes.

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS): genetic and clinical aspects

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) typically presents in middle life with a combination of neuropathy, ataxia and vestibular disease, with patients reporting progressive imbalance, oscillopsia, sensory disturbance and a dry cough. Examination identifies a sensory neuropathy or neuronopathy and bilaterally impaired vestibulo-ocular reflex. The underlying genetic basis is of biallelic AAGGG expansions in the second intron of replication factor complex subunit 1 (RFC1). The frequency and phenotype spectrum of RFC1 disease is expanding, ranging from typical CANVAS to site-restricted variants affecting the sensory nerves, cerebellum and/or the vestibular system. Given the wide phenotype spectrum of RFC1, the differential diagnosis is broad. RFC1 disease due to biallelic AAGGG expansions is probably the most common cause of recessive ataxia. The key to suspecting the disease (and prompt genetic testing) is a thorough clinical examination assessing the three affected systems and noting the presence of chronic cough.

Anaesthesia techniques and advanced monitoring in CANVAS patients - Implications for postoperative morbidity and patient recovery: A case report

Introduction

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a rare multisystem neurodegenerative disorder. We describe our perioperative evaluation and care of a patient with CANVAS undergoing a pancreaticoduodenectomy for an ampullary adenocarcinoma, with a focus on perioperative risk stratification and optimisation, intraoperative advanced haemodynamic monitoring and the postoperative care.

Case presentation

A 69-year-old female with CANVAS presented with asymptomatic obstructive jaundice, icterus and abdominal pain. She had limited mobility and deconditioning due to severe generalised neuropathy. Computed tomography confirmed a resectable periampullary tumour. Her Duke Activity Status Index was 8.25 points and Edmonton Frailty Scale score was 11, confirming moderate frailty. However, the Charlson Comorbidity Index was five, indicative of a 21% estimated 10-year survival. Further risk stratification including respiratory function testing, echocardiography and cardiopulmonary exercise testing was conducted. The patient proceeded with surgery after multidisciplinary discussions with her treating medical teams.

Discussion

CANVAS is a rare and challenging condition requiring careful perioperative planning and management. There is no effective treatment for CANVAS. The management approach focuses on mitigating symptoms and improving quality of life. Given that no specific guidelines for managing these patients in the perioperative period have been provided, this report highlights several critical medical issues and implications that should be considered for the successful management of these patients. We demonstrate the role of specific anaesthesia techniques and advanced haemodynamic monitoring in both preventing postoperative morbidity and optimising patient recovery.

Conclusion

CANVAS is a rare and challenging condition in anaesthesia requiring careful perioperative planning and management.

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CANVAS is a rare multisystem neurological disorder

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There is no effective treatment for CANVAS

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Perioperative management for patients with CANVAS is complex

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Perioperative risk stratification requires multidisciplinary involvement

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CANVAS patients can present with unique anaesthesia challenges

Cerebellar ataxia, neuropathy, vestibular areflexia syndrome: genetic and clinical insights

PURPOSE OF REVIEW

This review aims to summarise the present cerebellar ataxia, neuropathy, vestibular ataxia syndrome (CANVAS) literature, providing both clinical and genetic insights that might facilitate the timely clinical and genetic diagnosis of this disease.

RECENT FINDINGS

Recent advancements in the range of the clinical features of CANVAS have aided the development of a broader, more well-defined clinical diagnostic criteria. Additionally, the identification of a biallelic repeat expansion in RFC1 as the cause of CANVAS and a common cause of late-onset ataxia has opened the door to the potential discovery of a pathogenic mechanism, which in turn, may lead to therapeutic advancements and improved patient care.

SUMMARY

The developments in the clinical and genetic understanding of CANVAS will aid the correct and timely diagnosis of CANVAS, which continues to prove challenging within the clinic. The insights detailed within this review will raise the awareness of the phenotypic spectrum and currently known genetics. We also speculate on the future directions of research into CANVAS.

A novel RFC1 repeat motif (ACAGG) in two Asia-Pacific CANVAS families

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a progressive late-onset, neurological disease. Recently, a pentanucleotide expansion in intron 2 of RFC1 was identified as the genetic cause of CANVAS. We screened an Asian-Pacific cohort for CANVAS and identified a novel RFC1 repeat expansion motif, (ACAGG)exp, in three affected individuals. This motif was associated with additional clinical features including fasciculations and elevated serum creatine kinase. These features have not previously been described in individuals with genetically-confirmed CANVAS. Haplotype analysis showed our patients shared the same core haplotype as previously published, supporting the possibility of a single origin of the RFC1 disease allele. We analysed data from >26 000 genetically diverse individuals in gnomAD to show enrichment of (ACAGG) in non-European populations.

A Māori specific RFC1 pathogenic repeat configuration in CANVAS, likely due to a founder allele

Cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS) is a recently recognized neurodegenerative disease with onset in mid- to late adulthood. The genetic basis for a large proportion of Caucasian patients was recently shown to be the biallelic expansion of a pentanucleotide (AAGGG)n repeat in RFC1. Here, we describe the first instance of CANVAS genetic testing in New Zealand Māori and Cook Island Māori individuals. We show a novel, possibly population-specific CANVAS configuration (AAAGG)10-25(AAGGG)exp, which was the cause of CANVAS in all patients. There were no apparent phenotypic differences compared with European CANVAS patients. Presence of a common disease haplotype among this cohort suggests this novel repeat expansion configuration is a founder effect in this population, which may indicate that CANVAS will be especially prevalent in this group. Haplotype dating estimated the most recent common ancestor at ∼1430 ce. We also show the same core haplotype as previously described, supporting a single origin of the CANVAS mutation.

Current and future applications of ultrasound imaging in peripheral nerve disorders

Neuromuscular ultrasound (NMUS) is a rapidly evolving technique used in neuromuscular medicine to provide complimentary information to standard electrodiagnostic studies. NMUS provides a dynamic, real time assessment of anatomy which can alter both diagnostic and management pathways in peripheral nerve disorders. This review describes the current and future techniques used in NMUS and details the applications and developments in the diagnosis and monitoring of compressive, hereditary, immune-mediated and axonal peripheral nerve disorders, and motor neuron diseases. Technological advances have allowed the increased utilisation of ultrasound for management of peripheral nerve disorders; however, several practical considerations need to be taken into account to facilitate the widespread uptake of this technique.

Neuromuscular ultrasound for taxane peripheral neuropathy in breast cancer

BACKGROUND

Our study aim was to evaluate neuromuscular ultrasound (NMUS) for the assessment of taxane chemotherapy-induced peripheral neuropathy (CIPN), the dose-limiting toxicity of this agent.

METHODS

This cross-sectional study of breast cancer patients with taxane CIPN measured nerve cross-sectional area (CSA) by NMUS and compared with healthy historical controls. Correlations were determined between CSA and symptom scale, nerve conduction studies, and intraepidermal nerve fiber density (IENFD).

RESULTS

A total of 20 participants reported moderate CIPN symptoms at a median of 3.8 months following the last taxane dose. Sural nerve CSA was 1.2 mm² smaller than healthy controls (P ≤ .01). Older age and time since taxane were associated with smaller sural nerve CSA. For each 1 mm² decrease in sural nerve CSA, distal IENFD decreased by 2.1 nerve/mm (R² 0.30; P = .04).

CONCLUSIONS

These data support a sensory predominant taxane neuropathy or neuronopathy and warrant future research on longitudinal NMUS assessment of CIPN.

Cerebellar ataxia, neuropathy, vestibular areflexia syndrome due to RFC1 repeat expansion

Ataxia, causing imbalance, dizziness and falls, is a leading cause of neurological disability. We have recently identified a biallelic intronic AAGGG repeat expansion in replication factor complex subunit 1 (RFC1) as the cause of cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) and a major cause of late onset ataxia. Here we describe the full spectrum of the disease phenotype in our first 100 genetically confirmed carriers of biallelic repeat expansions in RFC1 and identify the sensory neuropathy as a common feature in all cases to date. All patients were Caucasian and half were sporadic. Patients typically reported progressive unsteadiness starting in the sixth decade. A dry spasmodic cough was also frequently associated and often preceded by decades the onset of walking difficulty. Sensory symptoms, oscillopsia, dysautonomia and dysarthria were also variably associated. The disease seems to follow a pattern of spatial progression from the early involvement of sensory neurons, to the later appearance of vestibular and cerebellar dysfunction. Half of the patients needed walking aids after 10 years of disease duration and a quarter were wheelchair dependent after 15 years. Overall, two-thirds of cases had full CANVAS. Sensory neuropathy was the only manifestation in 15 patients. Sixteen patients additionally showed cerebellar involvement, and six showed vestibular involvement. The disease is very likely to be underdiagnosed. Repeat expansion in RFC1 should be considered in all cases of sensory ataxic neuropathy, particularly, but not only, if cerebellar dysfunction, vestibular involvement and cough coexist.

Nerve ultrasound reference data in children from two to seven years

OBJECTIVE

We examined selected peripheral and spinal nerves of children aged between two and seven years.

METHOD

High resolution ultrasound was performed in 116 children (2-7 years of age) at 19 predefined landmarks of median, ulnar, tibial, fibular, sural and radial nerves, the vagus as well as cervical spinal nerve 5 and 6. Further, side-to-side measuring and grey-scale analysis was done at selected nerve sites.

RESULTS

Nerves of children were on average smaller than those of adults. Nerve growth correlates significantly with age in all nerves, the mean values were similar in the age of two to four years and five to seven years. Body mass index (BMI) and gender showed moderate effect at some nerve sites, however not uniformly in all. A side-to-side difference of up to 30% in median, and up to 20% in tibial nerve can occur in healthy individuals. Grey-scale analysis for echointensity has been performed in median, ulnar and tibial nerves.

CONCLUSION

Nerve size increases with age, BMI and gender have moderate effect. A side-to-side-difference of up to 30% can exist.

SIGNIFICANCE

Reference values of nerve cross-sectional area, side-to-side-difference and echo intensity are necessary to detect nerve pathology in children as well as in adults.

Spinocerebellar ataxia type 2-neuronopathy or neuropathy?

INTRODUCTION

Use of peripheral nerve ultrasound alongside standard electrodiagnostic tests may help to gain insight into the pathophysiology of peripheral nerve involvement in type 2 spinocerebellar ataxia (SCA2).

METHODS

Twenty-seven patients with SCA2 underwent ultrasound cross-sectional area (CSA) measurement of median, ulnar, sural and tibial nerves, and motor (median, ulnar, tibial) and sensory (median, ulnar, radial, sural) nerve conduction studies.

RESULTS

Twenty patients had pathologically small-nerve CSAs, suggestive of sensory neuronopathy. In these patients, electrophysiology showed non-length-dependent sensory neuropathy (14 of 20), "possible sensory neuropathy" (1 of 20), or normal findings (5 of 20). Four different patients had length-dependent sensory neuropathy on electrophysiology, and 1 had enlarged nerve CSAs. Regression analysis showed an inverse relationship between ataxia scores and upper limb nerve CSA (P < 0.03).

DISCUSSION

Our findings suggest that a majority of patients with SCA2 (74%) have a sensory neuronopathy and this correlates with disability. A minority of patients have findings consistent with axonal neuropathy (18%). Muscle Nerve, 2019.

Biallelic expansion of an intronic repeat in RFC1 is a common cause of late-onset ataxia

Late-onset ataxia is common, often idiopathic, and can result from cerebellar, proprioceptive, or vestibular impairment; when in combination, it is also termed cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We used non-parametric linkage analysis and genome sequencing to identify a biallelic intronic AAGGG repeat expansion in the replication factor C subunit 1 (RFC1) gene as the cause of familial CANVAS and a frequent cause of late-onset ataxia, particularly if sensory neuronopathy and bilateral vestibular areflexia coexist. The expansion, which occurs in the poly(A) tail of an AluSx3 element and differs in both size and nucleotide sequence from the reference (AAAAG)11 allele, does not affect RFC1 expression in patient peripheral and brain tissue, suggesting no overt loss of function. These data, along with an expansion carrier frequency of 0.7% in Europeans, implies that biallelic AAGGG expansion in RFC1 is a frequent cause of late-onset ataxia.

Nerve ultrasound as a diagnostic tool for sensory neuronopathy in spinocerebellar ataxia syndrome

OBJECTIVE

The objective was to assess if nerve ultrasound has a role in diagnosing sensory neuronopathy in spinocerebellar ataxia syndrome (SCA) by examining if proposed diagnostic cut-off criteria of ultrasound in sensory neuronopathy caused by cerebellar ataxia neuropathy vestibular areflexia syndrome (CANVAS) were also discriminatory for SCA-related sensory neuronopathy.

METHODS

Optimal diagnostic cut-off criteria for nerve size measured by diagnostic ultrasound were developed in 14 patients with CANVAS and 42 healthy controls using six peripheral nerve sites; and logistic regression and receiver operating characteristic (ROC) curves. These proposed cut-off values were tested in seven patients with spinocerebellar ataxia type 2 (SCA2) patients with sensory neuronopathy.

RESULTS

Ultrasound of upper limb nerves was highly accurate in differentiating between CANVAS and healthy controls with areas under the ROC curves between 0.97 and 0.99. Optimal cut-off measurements from the CANVAS patients also accurately diagnosed sensory neuronopathy in all patients with SCA2.

CONCLUSIONS

Upper limb ultrasound is a sensitive tool for detecting sensory neuronopathy in established cases of CANVAS and SCA2.

SIGNIFICANCE

Ultrasound could aid the diagnosis of sensory neuronopathy in spinocerebellar ataxias.

Indications for neuromuscular ultrasound: Expert opinion and review of the literature

Over the last two decades, dozens of applications have emerged for ultrasonography in neuromuscular disorders. We wanted to measure its impact on practice in laboratories where the technique is in frequent use. After identifying experts in neuromuscular ultrasound and electrodiagnosis, we assessed their use of ultrasonography for different indications and their expectations for its future evolution. We then identified the earliest papers to provide convincing evidence of the utility of ultrasound for particular indications and analyzed the relationship of their date of publication with expert usage. We found that experts use ultrasonography often for inflammatory, hereditary, traumatic, compressive and neoplastic neuropathies, and somewhat less often for neuronopathies and myopathies. Usage significantly correlated with the timing of key publications in the field. We review these findings and the extensive evidence supporting the value of neuromuscular ultrasound. Advancement of the field of clinical neurophysiology depends on widespread translation of these findings.