Discrimination of spinal and bulbar muscular atrophy from amyotrophic lateral sclerosis using sensory nerve action potentials

Characteristics of Sensory Neuron Dysfunction in Amyotrophic Lateral Sclerosis (ALS): Potential for ALS Therapy

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterised by the progressive degeneration of motor neurons, resulting in muscle weakness, paralysis, and, ultimately, death. Presently, no effective treatment for ALS has been established. Although motor neuron dysfunction is a hallmark of ALS, emerging evidence suggests that sensory neurons are also involved in the disease. In clinical research, 30% of patients with ALS had sensory symptoms and abnormal sensory nerve conduction studies in the lower extremities. Peroneal nerve biopsies show histological abnormalities in 90% of the patients. Preclinical research has reported several genetic abnormalities in the sensory neurons of animal models of ALS, as well as in motor neurons. Furthermore, the aggregation of misfolded proteins like TAR DNA-binding protein 43 has been reported in sensory neurons. This review aims to provide a comprehensive description of ALS-related sensory neuron dysfunction, focusing on its clinical changes and underlying mechanisms. Sensory neuron abnormalities in ALS are not limited to somatosensory issues; proprioceptive sensory neurons, such as MesV and DRG neurons, have been reported to form networks with motor neurons and may be involved in motor control. Despite receiving limited attention, sensory neuron abnormalities in ALS hold potential for new therapies targeting proprioceptive sensory neurons.

Genotype and clinical phenotype analysis of a Family with Kennedy disease

To investigate the clinical phenotype-genotype correlations of a family with Kennedy disease (KD) and improve our understanding of the disease. KD was confirmed after clinical phenotypic analyses, laboratory tests, polymerase chain reaction assays for cytosine-adenine-guanine (CAG) repeats, and neuro-electrophysiological tests. The disease was assessed using the KD1234 scale and the spinal and bulbar muscular atrophy functional rating scale. The average age of disease onset was 30.8 ± 2.85 years. Clinically diagnosed members had 48 CAG repeats (≥35 is abnormal) in the androgen receptor gene. The patients exhibited gynecomastia and testicular dysfunction. The lesions mainly involved the medulla oblongata and spinal cord. Progesterone and serum creatine kinase levels were significantly high. Electromyography showed chronic neurogenic damage and abnormal sensory and motor conduction in family members who did not participate in sports, exercise, or physical hobbies. Our study showed that this family had a stable inheritance of CAG repeats, and the genotype was consistent with the clinical phenotype. Gynecomastia was the first symptom, with progressive androgen resistance resulting in testicular atrophy, infertility, and sexual dysfunction. Changes in serum creatine kinase may indicate the progression or relief of symptoms, and rehabilitation may delay the progression of muscle atrophy.

Mexiletine in spinal and bulbar muscular atrophy: a randomized controlled trial

Objective

Patients with spinal and bulbar muscular atrophy (SBMA) often experience muscular weakness under cold exposure.

Methods

In our previously conducted observational study, we assessed nerve conduction and grip strength to examine the effect of cold exposure on motor function, based on which we conducted a randomized controlled trial to evaluate the efficacy and safety of mexiletine hydrochloride in SBMA (MEXPRESS).

Results

In the observational study, 51 consecutive patients with SBMA and 18 healthy controls (HCs) were enrolled. Of the patients with SBMA, 88.0% experienced cold paresis. Patients with SBMA exhibited greater prolongation of ulnar nerve distal latency under cold (SBMA, 5.6 ± 1.1 msec; HC, 4.3 ± 0.6 msec; p <0.001); the change in the distal latencies between room temperature and cold exposure conditions correlated with the change in grip power. In the MEXPRESS trial, 20 participants took mexiletine or lactose, three times a day for 4 weeks with a crossover design. There was no difference in distal latencies at room temperature and under cold exposure between mexiletine and placebo groups as the primary endpoint. However, tongue pressure and 10‐sec grip and release test under cold exposure were improved in the mexiletine group. There were no serious adverse events throughout the study period.

Interpretation

Cold paresis is common and associated with prolongation of distal latency in SBMA. The results of the phase II clinical trial revealed that mexiletine showed short‐term safety, but it did not restore cold exposure‐induced prolongation of distal latency.

Clinical implication of denervation in sporadic inclusion body myositis

INTRODUCTION

Sporadic inclusion body myositis (sIBM) is often accompanied by signs suggestive of denervation on electromyography (EMG), which mimics neurogenic disorders. Hence, the current study aimed to assess reinnervation after denervation in sIBM and its clinical impllcation.

METHODS

We retrospectively examined consecutive muscle biopsy specimens collected from 109 sIBM patients who were referred to our institution for diagnostic muscle biopsy from 2001 to 2018. Reinnervation after denervation in sIBM patients was assessed via muscle biopsy and EMG. The levels of acetylcholine receptor subunit γ (Chrng) and muscle-specific kinase (MuSK) mRNA, which are markers of denervation, were examined using real-time polymerase chain reaction. Response to treatment was defined as an increase of grade 1 or higher in two or more muscle groups as assessed using the Medical Research Council scale.

RESULTS

In total, 93 (85.3%) of 109 sIBM patients had reinnervation after denervation on histological examination and/or EMG. The mean disease duration before biopsy was significantly longer in patients with reinnervation after denervation than in those without (p < 0.00001). Patients with denervation had significantly higher levels of Chrng and MuSK mRNA than those without. The proportion of patients who responded to immunosuppressive therapies was smaller in the patients with denervation than those without (p < 0.05). However, there was no significant difference regarding time from onset to using a walking aid between the two groups.

DISCUSSION

Reinnervation after denervation is associated with disease duration and short-term response to therapy in individuals with sIBM.

Amyotrophic lateral sclerosis mimics

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disorder characterized by progressive degeneration of cortical, bulbar, and spinal motor neurons. When a patient presents with a progressive upper and/or lower motor syndrome, clinicians must pay particular attention to any atypical features in the history and/or clinical examination suggesting an alternate diagnosis, as up to 10% percent of patients initially diagnosed with ALS have a mimic of ALS. ALS is a clinical diagnosis and requires the exclusion of other disorders that may have similar presentations but a more favorable prognosis or an effective therapy. Because there is currently no specific diagnostic biomarker that is sensitive or specific for ALS, understanding the spectrum of clinical presentations of ALS and its mimics is paramount. While true mimics of ALS are rare, the clinician must correctly identify these disorders to avoid the misdiagnosis of ALS and to initiate effective treatment where available.

Evaluation of peripherin in biofluids of patients with motor neuron diseases

Peripherin (PRPH), a type III intermediate filament, assembles with neurofilaments in neurons of the peripheral nervous system, including lower motor neurons (LMN). To evaluate the role of PRPH in LMN degeneration, we assessed PRPH and neurofilament light chain (NfL) in cerebrospinal fluid (CSF) and serum of 91 patients with motor neuron diseases (MND) and 69 controls. Overall, we found PRPH to be more concentrated in serum than in CSF. Serum PRPH resulted significantly increased in MND patients but it was unrelated to CSF‐NfL or survival in the amyotrophic lateral sclerosis (ALS) subset. PRPH might represent a marker of LMN involvement.

Myoglobin: a new biomarker for spinal and bulbar muscular atrophy?

OBJECTIVES

There is a primary muscular affection in spinal and bulbar muscular atrophy (SBMA). Myoglobin (Myo) is mainly distributed in the myocardium and skeletal muscle. The purpose of the study was to explore the significance of serum Myo detection in the diagnosis and clinical evaluation of SBMA.

MATERIALS AND METHODS

In this study, serum creatine kinase (CK), Myo, and Troponin T (cTNT) levels were assessed in 80 patients with SBMA and were compared with those of 60 patients with amyotrophic lateral sclerosis (ALS). All measurement data were analyzed using the t-test and enumeration data using the χ2-test.

RESULTS

The rate of abnormal Myo levels in the SBMA group was 100%, however, none of the patients with ALS had an abnormal Myo level. There was no overlap between the two groups. The Myo levels in patients with SBMA were correlated with the course of the disease. Further, their CK level was significantly elevated compared with that in patients with ALS, however, there was an overlap between the two groups. The serum cTNT level in patients with SBMA was not significantly different from that in patients with ALS.

CONCLUSION

Myo, as a simple, inexpensive, and readily available biochemical indicator, is likely to be used for the differentiation between SBMA and ALS, and used as a new biomarker for the clinical evaluation of SBMA.

A nerve conduction study predicts the prognosis of sporadic amyotrophic lateral sclerosis

OBJECTIVE

To clarify the relationship between nerve conduction study (NCS) and prognosis in patients with amyotrophic lateral sclerosis (ALS).

METHODS

We included 190 patients with sporadic ALS. We used onset age, sex, onset site (bulbar vs. spinal), revised El Escorial criteria category (definite vs. others), and the King's clinical systems, and the Milano-Torino (MiToS) functional staging systems, and decline rates of revised ALS functional rating scale (ALSFRS-R) as known prognostic factors. An NCS was performed on the median, ulnar, tibial, and sural nerves. The endpoint was death or the introduction of tracheostomy positive-pressure ventilation. Multivariate analysis for each NCS variable, known prognostic factors was performed using Cox stepwise proportional hazards analysis. Univariate analysis was performed for NCS variables that showed a significant association with prognosis in multivariate analysis. Survival was analyzed with a Kaplan-Meier curve and log-rank test.

RESULTS

The Cox model identified the compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) amplitudes of the median nerve as prognostic factors. In the log-rank test, patients with higher median nerve CMAP amplitude had a significantly better prognosis than those with lower amplitude, regardless of age. And prognosis was better in the group with lower median nerve SNAP amplitude only in patients younger than the 25th percentile (~ 57 years).

CONCLUSIONS

CMAP and SNAP amplitudes of the median nerve are considered to be independent prognostic factors of sporadic ALS.

The French national protocol for Kennedy's disease (SBMA): consensus diagnostic and management recommendations

Background

Kennedy’s disease (KD), also known as spinal and bulbar muscular atrophy (SBMA), is a rare, adult-onset, X-linked recessive neuromuscular disease caused by CAG expansions in exon 1 of the androgen receptor gene (AR). The objective of the French national diagnostic and management protocol is to provide evidence-based best practice recommendations and outline an optimised care pathway for patients with KD, based on a systematic literature review and consensus multidisciplinary observations.

Results

The initial evaluation, confirmation of the diagnosis, and management should ideally take place in a tertiary referral centre for motor neuron diseases, and involve an experienced multidisciplinary team of neurologists, endocrinologists, cardiologists and allied healthcare professionals. The diagnosis should be suspected in an adult male presenting with slowly progressive lower motor neuron symptoms, typically affecting the lower limbs at onset. Bulbar involvement (dysarthria and dysphagia) is often a later manifestation of the disease. Gynecomastia is not a constant feature, but is suggestive of a suspected diagnosis, which is further supported by electromyography showing diffuse motor neuron involvement often with asymptomatic sensory changes. A suspected diagnosis is confirmed by genetic testing. The multidisciplinary assessment should ascertain extra-neurological involvement such as cardiac repolarisation abnormalities (Brugada syndrome), signs of androgen resistance, genitourinary abnormalities, endocrine and metabolic changes (glucose intolerance, hyperlipidemia). In the absence of effective disease modifying therapies, the mainstay of management is symptomatic support using rehabilitation strategies (physiotherapy and speech therapy). Nutritional evaluation by an expert dietician is essential, and enteral nutrition (gastrostomy) may be required. Respiratory management centres on the detection and treatment of bronchial obstructions, as well as screening for aspiration pneumonia (chest physiotherapy, drainage, positioning, breath stacking, mechanical insufflation-exsufflation, cough assist machnie, antibiotics). Non-invasive mechanical ventilation is seldom needed. Symptomatic pharmaceutical therapy includes pain management, endocrine and metabolic interventions. There is no evidence for androgen substitution therapy.

Conclusion

The French national Kennedy’s disease protocol provides management recommendations for patients with KD. In a low-incidence condition, sharing and integrating regional expertise, multidisciplinary experience and defining consensus best-practice recommendations is particularly important. Well-coordinated collaborative efforts will ultimately pave the way to the development of evidence-based international guidelines.

Monozygotic Twins Discordant for Kennedy Disease: A Case Report

Spinal and bulbar muscular atrophy or Kennedy disease (KD) is an X-linked recessive disorder caused by a pathogenic CAG expansion in the first exon of the androgen receptor. Proximal muscle atrophy, weakness, contraction fasciculations, bulbar involvement, and sensory disturbances are part of the clinical picture of KD. We report the unusual genetic and phenotypic expression in 2 monozygotic twins. Genetic analysis has shown abnormal expansion of CAG repeat in the first exon of the androgen receptor gene on chromosome X different between the twin brothers (44, respectively, 46) but with large phenotypical differences including onset age, evolution, and clinical features. Disease began at age 31 for the first brother, respectively, and at 56 years for the second one and consisted of muscle wasting and progressive impairment of walking. In addition, the second brother did not manifest bulbar involvement 3 years after clinical onset and has more sensory features. Besides classical EMG testing, we evaluate sensory participation in spinal and bulbar muscular atrophy with sudoscan device and confirmed the sensory deficit. We discussed epigenetic factors potentially involved in KD that could play a role in the phenotypical differences. To the best of our knowledge, this is the first case describing CAG trinucleotide repeats in monozygotic twins and also the first sudoscan diagnostic of sensory disturbances in Kennedy syndrome.

Amyotrophic lateral sclerosis or not: Keys for the diagnosis

Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron disease (MND) which prognosis is poor. Early diagnosis permit to set up immediately adapted treatment and cares. Available diagnostic criteria are based on the detection of both central and peripheral motor neuron injury in bulbar, cervical, thoracic and lumbar regions. Electrodiagnostic (EDX) tests are the key tools to identify peripheral motor neuron involvement. Needle examination records abnormal activities at rest, and looks for neurogenic pattern during muscle contraction. Motor unit potentials morphology is modified primary to recruitment. Motor evoked potentials remain the test of choice to identify impairment of central motor neurons. In the absence of diagnostic biomarker of ALS and among essential investigations of suspected MND, a careful clinical and neurophysiological work-up is essential to rule out the differential diagnosis.

Differences in F-Wave Characteristics between Spinobulbar Muscular Atrophy and Amyotrophic Lateral Sclerosis

There is limited data on the differences in F-wave characteristics between spinobulbar muscular atrophy (SBMA) and lower motor neuron dominant (LMND) amyotrophic lateral sclerosis (ALS). We compared the parameters of F-waves recorded bilaterally from the median, ulnar, tibial, and deep peroneal nerves in 32 SBMA patients, 37 patients with LMND ALS, and 30 normal controls. The maximum F-wave amplitudes, frequencies of giant F-waves, and frequencies of patients with giant F-waves in all nerves examined were significantly higher in the SBMA patients than in the ALS patients and the normal controls. The mean F-wave amplitude, maximum F-wave amplitude, frequency of giant F-waves, and frequency of patients with giant F-waves in the median and deep peroneal nerves were comparable between the ALS patients and normal controls. Giant F-waves were detected in multiple nerves and were often symmetrical in the SBMA patients compared with the ALS patients. The number of nerves with giant F-waves seems to be the most robust variable for differentiation of SBMA from ALS, with an area under the curve of 0.908 (95% CI: 0.835–0.982). A cut-off value of the number of nerves with giant F-waves (≥3) for diagnosing SBMA showed high sensitivity and specificity: 85% sensitivity and 81% specificity vs. ALS patients. No significant correlations were found between the pooled frequency of giant F-waves and disease duration in the SBMA (r = 0.162, P = 0.418) or ALS groups (r = 0.107, P = 0.529). Our findings suggested that F-waves might be used to discriminate SBMA from ALS, even at early stages of disease.

Diagnostic Clinical, Electrodiagnostic and Muscle Pathology Features of Spinal and Bulbar Muscular Atrophy

Kennedy's disease or spinal and bulbar muscular atrophy (SBMA) is a multi-system disorder affecting adult males, which is characterized by weakness of limbs and faciobulbar muscles primarily due to loss of lower motor neurons. Besides the obvious motor neuronopathy, additional findings in a substantial proportion of SBMA patients include sensory neuropathy and signs of androgen deficiency, such as poor sexual functioning and reduced fertility with gynaecomastia. The presence of elevated glucose, liver pathology or dyslipidaemia is less consistent features. We review the striking clinical, electrodiagnostic and muscle pathology features characteristic of Kennedy's disease, which has some peculiar and diagnostically useful features not observed in many other neuromuscular disorders.

Spinal and Bulbar Muscular Atrophy

Spinal and bulbar muscular atrophy, or Kennedy disease, is a slowly progressive X-linked neuromuscular disease caused by a trinucleotide (CAG) repeat expansion in the androgen receptor gene. Affected males typically develop weakness in their mid-40s as well as evidence of androgen insensitivity with reduced fertility and gynecomastia. Diagnosis is often delayed because of decreased awareness of the disease, although genetic testing allows for direct diagnosis. Therapeutic strategies to block the toxicity of the mutant androgen receptor have been unsuccessful thus far, and evaluation of additional candidate therapies is underway.

Spontaneous activity in electromyography may differentiate certain benign lower motor neuron disease forms from amyotrophic lateral sclerosis

There is limited data on electromyography (EMG) findings in other motor neuron disorders than amyotrophic lateral sclerosis (ALS). We assessed whether the distribution of active denervation detected by EMG, i.e. fibrillations and fasciculations, differs between ALS and slowly progressive motor neuron disorders. We compared the initial EMG findings of 43 clinically confirmed, consecutive ALS patients with those of 41 genetically confirmed Late-onset Spinal Motor Neuronopathy and 14 Spinal and Bulbar Muscular Atrophy patients. Spontaneous activity was more frequently detected in the first dorsal interosseus and deltoid muscles of ALS patients than in patients with the slowly progressive motor neuron diseases. The most important observation was that absent fibrillations in the first dorsal interosseus muscle identified the benign forms with sensitivities of 66%-77% and a specificity of 93%. The distribution of active denervation may help to separate ALS from mimicking disorders at an early stage.

Genotype-phenotype correlation in Chinese patients with spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is an X-linked recessive motor neuron disease characterized by slowly progressive weakness and atrophy of proximal limbs and bulbar muscles. To assess the genotype-phenotype correlation in Chinese patients, we identified 155 patients with SBMA and retrospectively examined available data from laboratory tests and neurophysiological analyses. Correlations between genotype and phenotype were analyzed. There was an inverse correlation between the length of CAG repeats and age at first muscle weakness (p<0.0001). The serum creatine kinase level showed a significant inverse correlation with disease duration and the age at examination (p=0.019 and p=0.004, respectively). Unlike previous classification of motor- and sensory-dominant phenotypes, all findings of nerve conduction, except the amplitudes of median nerve compound motor action potential, were positively correlated to the length of CAG repeats. A significant decline in sensory nerve action potential amplitudes may assist differential diagnosis of SBMA.

Kennedy disease with biphasic clinical course and rapid progression

We report a case of spinal and bulbar muscular atrophy (SBMA), also known as Kennedy disease, with a 38 CAG-repeat expansion in exon-1 of the androgen receptor gene, presenting with a 2-year history of mild speech difficulty, dysphonia, and occasional choking. Initial clinical features and complementary studies were consistent with SBMA. The disease progression, as assessed by the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised, remained stable over the first 5 years from the onset but showed a rapid decline (from 42 to 24 points) over the next 18 months before his death. In the later stages of the disease, deep tendon reflexes were preserved in limbs and a brisk jaw-jerk reflex and bilateral Hoffmann sign were evident. Survival from disease onset was 78 months. The final cause of death was aspiration pneumonia. The atypical clinical features, evolution, and accelerated disease course are not concordant with the relatively short 38 CAG-repeat expansion in the androgen receptor gene. This may represent either a variant SBMA phenotype, which has not been recorded to date, or the development of amyotrophic lateral sclerosis in a known case of SBMA.

Connexin- and pannexin-based channels in normal skeletal muscles and their possible role in muscle atrophy

Precursor cells of skeletal muscles express connexins 39, 43 and 45 and pannexin1. In these cells, most connexins form two types of membrane channels, gap junction channels and hemichannels, whereas pannexin1 forms only hemichannels. All these channels are low-resistance pathways permeable to ions and small molecules that coordinate developmental events. During late stages of skeletal muscle differentiation, myofibers become innervated and stop expressing connexins but still express pannexin1 hemichannels that are potential pathways for the ATP release required for potentiation of the contraction response. Adult injured muscles undergo regeneration, and connexins are reexpressed and form membrane channels. In vivo, connexin reexpression occurs in undifferentiated cells that form new myofibers, favoring the healing process of injured muscle. However, differentiated myofibers maintained in culture for 48 h or treated with proinflammatory cytokines for less than 3 h also reexpress connexins and only form functional hemichannels at the cell surface. We propose that opening of these hemichannels contributes to drastic changes in electrochemical gradients, including reduction of membrane potential, increases in intracellular free Ca(2+) concentration and release of diverse metabolites (e.g., NAD(+) and ATP) to the extracellular milieu, contributing to multiple metabolic and physiologic alterations that characterize muscles undergoing atrophy in several acquired and genetic human diseases. Consequently, inhibition of connexin hemichannels expressed by injured or denervated skeletal muscles might reduce or prevent deleterious changes triggered by conditions that promote muscle atrophy.

Pathogenesis and therapy of spinal and bulbar muscular atrophy (SBMA)

Spinal and bulbar muscular atrophy (SBMA) is a late-onset motor neuron disease characterized by slowly progressive muscle weakness and atrophy. During the last two decades, basic and clinical research has provided important insights into the disease phenotype and pathophysiology. The cause of SBMA is the expansion of a trinucleotide CAG repeat encoding a polyglutamine tract within the first exon of the androgen receptor (AR) gene. SBMA exclusively affects adult males, whereas females homozygous for the AR mutation do not manifest neurological symptoms. The ligand-dependent nuclear accumulation of the polyglutamine-expanded AR protein is central to the gender-specific pathogenesis of SBMA, although additional steps, e.g., DNA binding, inter-domain interactions, and post-translational modification of AR, modify toxicity. The interactions with co-regulators are another requisite for the toxic properties of the polyglutamine-expanded AR. It is also shown that the polyglutamine-expanded AR induces diverse molecular events, such as transcriptional dysregulation, axonal transport disruption, and mitochondrial dysfunction, which play causative roles in the neurodegeneration in SBMA. The pathogenic AR-induced myopathy also contributes to the non-cell autonomous degeneration of motor neurons. Pre-clinical studies using animal models show that the pathogenic AR-mediated neurodegeneration is suppressed by androgen inactivation, the efficacy of which has been tested in clinical trials. Pharmacological activation of cellular defense machineries, such as molecular chaperones, ubiquitin-proteasome system, and autophagy, also exerts neuroprotective effects in experimental models of SBMA.