Varied electrophysiologic patterns in spinocerebellar ataxia type 2

Polyneuropathy in Patients with Spinocerebellar Ataxias Types 2, 3, and 10: A Systematic Review

Spinocerebellar ataxia (SCA) is an autosomal dominant hereditary disease with a low prevalence, for which more than 50 types have been described. This group of neurodegenerative diseases can present as different phenotypes with varying progression rates and clinical manifestations of different severities. Herein, we systematically reviewed existing medical literature to describe the main characteristics of polyneuropathy in patients with SCA types 2, 3, and 10. Using relevant keywords, 16,972 articles were identified from the databases. Of these, 5,329 duplicate studies were excluded before screening. Subsequently, 11,643 studies underwent title and abstract review, of which only 49 were selected for full-text review. Among these, 24 studies were included. The medical literature suggests peripheral neuropathy - probably in a polyneuropathy phenotype - in SCA types 2 and 3. It is not possible to determine whether there is peripheral neuropathy in patients with SCA type 10, as there is only one case series in Mexico that described peripheral neuropathy in this group. Further studies are required to investigate peripheral neuropathy in patients with SCA types 2, 3, and 10. The study and description of a possible statistical association between CAG repeats and SARA scale scores with the presence of peripheral neuropathy are important points requiring assessment in future research.

Genetic spectrum in a cohort of patients with distal hereditary motor neuropathy

Background

Distal hereditary motor neuropathy (dHMN) is a heterogeneous group of diseases characterized by exclusive degeneration of peripheral motor nerves, while only 20.0–47.8% of dHMN patients are genetically identified. Recently, GGC expansion in the 5’UTR of NOTCH2NLC has been associated with dHMN. Accordingly, short tandem repeat (STR) should be further explored in genetically unsolved patients with dHMN.

Methods

A total of 128 patients from 90 unrelated families were clinically diagnosed as dHMN, and underwent a comprehensively genetic screening. Skin biopsies were conducted with routine protocols.

Results

Most patients showed chronic distal weakness of lower limbs (121/128), while 20 patients initially had asymmetrical involvements, 14 had subclinical sensory abnormalities, 11 had pyramidal impairments, five had cerebellar disturbance, and four had hyperCKmia. The rate of genetic detection was achieved in 36.7% (33/90), and the rate increased to 46.7% (42/90) if patients with variants uncertain significance were included. The most common causative genes included chaperone‐related genes (8/33, 24.2%), tRNA synthetase genes (4/33, 12.1%), and cytoskeleton‐related genes (4/33, 12.1%). Additionally, two dominant inherited families were attributed to abnormal expansion of GGC repeats in the 5‘UTR of NOTCH2NLC; and a patient with dHMN and cerebellar symptoms had CAG repeat expansion in the ATXN2 gene. Skin biopsy from patients with GGC expansion in NOTCH2NLC revealed typical intranuclear inclusions on histological and ultrastructural examinations.

Interpretations

This study further extends the genetic heterogeneity of dHMN. Given some dHMN patients may be associated with nucleotides repeat expansion, STR screening is necessary to perform in genetically unsolved patients.

Neurophysiological features in spinocerebellar ataxia type 2: Prospects for novel biomarkers

Electrophysiological biomarkers are useful to assess the degeneration and progression of the nervous system in pre-ataxic and ataxic stages of the Spinocerebellar Ataxia Type 2 (SCA2). These biomarkers are essentially defined by their clinical significance, discriminating patients and/or preclinical subjects from healthy controls in cross-sectional studies, their significant changes over time in longitudinal studies, and their correlation with the cytosine-guanine-adenine (CAG) repeat expansion and/or clinical ataxia scores, time of evolution and time to ataxia onset. We classified electrophysiological biomarkers into three main types: (1) preclinical, (2) disease progression and (3) genetic damage. We review the data that identify sural nerve potential amplitude, maximum saccadic velocity, sleep efficiency, rapid eye movement (REM) sleep percentage, K-complex density, REM sleep without atonia percentage, corticomuscular coherence, central motor conduction time, visual P300 latency, and antisaccadic error correction latency as reliable preclinical, progression and/or genetic damage biomarkers of SCA2. These electrophysiological biomarkers will facilitate the conduction of clinical trials that test the efficacy of emerging treatments in SCA2.

Myoclonus-Ataxia Syndromes: A Diagnostic Approach

Background

A myriad of disorders combine myoclonus and ataxia. Most causes are genetic and an increasing number of genes are being associated with myoclonus-ataxia syndromes (MAS), due to recent advances in genetic techniques. A proper etiologic diagnosis of MAS is clinically relevant, given the consequences for genetic counseling, treatment, and prognosis.

Objectives

To review the causes of MAS and to propose a diagnostic algorithm.

Methods

A comprehensive and structured literature search following PRISMA criteria was conducted to identify those disorders that may combine myoclonus with ataxia.

Results

A total of 135 causes of combined myoclonus and ataxia were identified, of which 30 were charted as the main causes of MAS. These include four acquired entities: opsoclonus-myoclonus-ataxia syndrome, celiac disease, multiple system atrophy, and sporadic prion diseases. The distinction between progressive myoclonus epilepsy and progressive myoclonus ataxia poses one of the main diagnostic dilemmas.

Conclusions

Diagnostic algorithms for pediatric and adult patients, based on clinical manifestations including epilepsy, are proposed to guide the differential diagnosis and corresponding work-up of the most important and frequent causes of MAS. A list of genes associated with MAS to guide genetic testing strategies is provided. Priority should be given to diagnose or exclude acquired or treatable disorders.

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.

Early corticospinal tract damage in prodromal SCA2 revealed by EEG-EMG and EMG-EMG coherence

OBJECTIVE

Clinical data suggest early involvement of the corticospinal tract (CST) in spinocerebellar ataxia type 2 (SCA2). Here we tested if early CST degeneration can be detected in prodromal SCA2 mutation carriers by electrophysiological markers of CST integrity.

METHODS

CST integrity was tested in 15 prodromal SCA2 mutation carriers, 19 SCA2 patients and 25 age-matched healthy controls, using corticomuscular (EEG-EMG) and intermuscular (EMG-EMG) coherence measures in upper and lower limb muscles.

RESULTS

Significant reductions of EEG-EMG and EMG-EMG coherences were observed in the SCA2 patients, and to a similar extent in the prodromal SCA2 mutation carriers. In prodromal SCA2, EEG-EMG and EMG-EMG coherences correlated with the predicted time to ataxia onset.

CONCLUSIONS

Findings indicate early CST neurodegeneration in SCA2. EEG-EMG and EMG-EMG coherence may serve as biomarkers of early CST neurodegeneration in prodromal SCA2 mutation carriers.

SIGNIFICANCE

Findings are important for developing preclinical disease markers in the context of currently emerging disease-modifying therapies of neurodegenerative disorders.

Pattern of Peripheral Nerve Involvement in Spinocerebellar Ataxia Type 2: a Neurophysiological Assessment

Peripheral neuropathy is frequent in spinocerebellar ataxia type 2 (SCA2), but the pattern and characteristics of nerve involvement are still an unsettled issue. This study aimed to evaluate the prevalence, extent, and distribution of nerve involvement in SCA2 patients through neurophysiological studies. Thirty-one SCA2 patients and 20 control subjects were enrolled in this study. All subjects were prospectively evaluated through electromyography, including nerve conduction, needle electromyography in proximal and distal muscles of the upper and lower limbs, and sural radial amplitude ratio (SRAR). We aimed to differentiate distal axonopathy from diffuse nerve commitment, characterizing neuronopathy. Nerve involvement was observed in 83.6 % (26 individuals) of SCA2 patients. Among these, 19 had diffuse sensory abnormalities on nerve conduction predominantly on the upper limbs, with diffuse chronic denervation on needle electromyography and elevated SRAR values. Four individuals had only diffuse sensory involvement, and 2 had only motor involvement on needle evaluation and normal nerve conduction. These were interpreted as neuronopathy due to the diffuse distribution of the involvement. One individual had distal sensory axonopathy, with lower limb predominance. In this study, we found neuronopathy as the main pattern of nerve involvement in SCA2 patients and that motor involvement is a frequent feature. This information brings new insights into the understanding of the pathophysiology of nerve involvement in SCA2 and sets some key points about the phenotype, which is relevant to guide the genetic/molecular diagnosis.

Peripheral Neuropathy in Spinocerebellar Ataxia Type 1, 2, 3, and 6

Spinocerebellar ataxias (SCAs) are characterized by autosomal dominantly inherited progressive ataxia but are clinically heterogeneous due to variable involvement of non-cerebellar parts of the nervous system. Non-cerebellar symptoms contribute significantly to the burden of SCAs, may guide the clinician to the underlying genetic subtype, and might be useful markers to monitor disease. Peripheral neuropathy is frequently observed in SCA, but subtype-specific features and subclinical manifestations have rarely been evaluated. We performed a multicenter nerve conduction study with 162 patients with genetically confirmed SCA1, SCA2, SCA3, and SCA6. The study proved peripheral nerves to be involved in the neurodegenerative process in 82 % of SCA1, 63 % of SCA2, 55 % of SCA3, and 22 % of SCA6 patients. Most patients of all subtypes revealed affection of both sensory and motor fibers. Neuropathy was most frequently of mixed type with axonal and demyelinating characteristics in all SCA subtypes. However, nerve conduction velocities of SCA1 patients were slower compared to other genotypes. SCA6 patients revealed less axonal damage than patients with other subtypes. No influence of CAG repeat length or biometric determinants on peripheral neuropathy could be identified in SCA1, SCA3, and SCA6. In SCA2, earlier onset and more severe ataxia were associated with peripheral neuropathy. We proved peripheral neuropathy to be a frequent site of the neurodegenerative process in all common SCA subtypes. Since damage to peripheral nerves is readily assessable by electrophysiological means, nerve conduction studies should be performed in a longitudinal approach to assess these parameters as potential progression markers.

Progression markers of Spinocerebellar ataxia 2. A twenty years neurophysiological follow up study

Nerve conduction is profoundly affected in Spinocerebellar ataxia 2 (SCA2) even before the onset of the disease, but there is no information regarding its progression to the final stage of SCA2. In order to study the progression patterns of nerve conduction abnormalities in SCA2 we performed a prospective follow up evaluation of sensory and motor conduction in 21 SCA2 mutation carriers-initially presymptomatics- and 19 non-SCA2 mutation carriers during 20years. The earliest electrophysiological alterations were the reduction of sensory amplitudes in median and sural nerves, which could be found 8 to 5years prior disease onset and in the last 4years of the preclinical stage respectively. These abnormalities were followed by the increase of sensory latencies and decrease of conduction velocities. Sensory amplitudes progressively decreased during the follow-up clinical stage, rendering almost all patients with abnormal amplitudes and lack of sensory potentials, with faster progression rates in patients with larger CAG repeat lengths. Peripheral motor nerves showed the later involvement. These findings were used to define three distinct stages that describe the progression of the peripheral neuropathy. We suggest that sensory amplitudes could be useful biomarkers to assess the progression of peripheral nerve involvement and therefore to evaluate future clinical trials of therapeutic agents.

Spinocerebellar ataxia type 2 (SCA2) in an Egyptian family presenting with polyphagia and marked CAG expansion in infancy

We describe an Egyptian family having SCA2 affecting three generations with marked molecular and clinical anticipation observed in the index case. Our proband was a male child starting as early as 2 years old with progressive extrapyramidal manifestations, slow eye movements and cognitive impairment. A history of nonspecific mild developmental delay was recorded. The patient lost all cognitive functions, had persistent dystonic posture, trophic changes, vasomotor instability, dysphagia and died at the age of 7 years. The age at presentation among other affected family members varied between 11 and 45 years old across three generations. The early common neurological symptoms were choreoathetotic movements, myoclonic jerk, gait difficulty, expressionless face and emotional liability. Later, overt ataxia, incoordination, dysarthria, mild dementia and slow eye saccades predominated. Brisk tendon reflexes were detected in three cases. Peripheral nerve affection was a late manifestation. Interestingly, polyphagia and obesity were striking manifestations in the middle stage of the disease; an observation that might support a previously suggested relation between the ataxin-2 gene and body weight. The proband showed an amplified allele with marked CAG expansion in the form of a smear sized 69-75 repeats resulted from maternal transmission. To our knowledge, our index case is the second report in the literature presenting with infantile onset SCA2 and intermediate repeat expansion. This family expands the phenotypic spectrum of early onset SCA2 and points out the importance of considering SCA2 gene analysis in children with progressive neurological impairment and abnormal movements with or without polyphagia.