Disease progression and outcome measures in spinobulbar muscular atrophy

271st ENMC international workshop: Towards a unifying effort to fight Kennedy's disease. 20-22 October 2023, Hoofddorp, Netherlands

The workshop held in the Netherlands from October 20-22, 2023, united 27 scientists from academia, healthcare, and industry representing 11 countries, alongside four patient and charity representatives. Focused on Kennedy's Disease (KD), also known as spinal and bulbar muscular atrophy (SBMA), the workshop aimed to consolidate knowledge, align on clinical trial designs, and promote participative medicine for effective treatments. Discussions emphasized KD's molecular mechanisms, highlighting its status as a neuromuscular disorder with motor neuron degeneration. Strategies for therapeutic intervention, including AR activity modulation and targeting post-translational modifications, were proposed. The need for diagnostic, prognostic, and target engagement biomarkers was stressed. Challenges in patient stratification and clinical trial recruitment were acknowledged, with the International KD/SBMA Registry praised for its role. The workshop concluded with a patient-focused session, underscoring challenges in KD diagnosis and the vital support provided by patient associations.

Whole-Body Muscle Magnetic Resonance Imaging in 81 Patients with Spinal and Bulbar Muscular Atrophy: A Prospective Study

OBJECTIVE

Spinal and bulbar muscular atrophy (SBMA) is characterized by slow, progressive bulbar and limb muscle weakness; however, the pattern of progression of muscle fat infiltration remains unclear. We assessed the progression of muscle involvement in 81 patients with SBMA using whole-body muscle magnetic resonance imaging (MRI), alongside clinical and laboratory findings.

METHODS

This prospective study included patients with genetically confirmed SBMA who underwent whole-body muscle MRI. We analyzed muscle fat infiltration and the pattern of involved muscles using cluster analysis, visualizing the sequential progression of fat infiltration. Muscle clusters demonstrated correlation with clinical scales and laboratory findings. Additionally, linear regression analysis was performed to identify the MRI section most strongly associated with 6-minute walk test (6MWT).

RESULTS

We included 81 patients with SBMA (age = 54.3 years). After categorizing the patients into 6 clusters based on the pattern of muscle fat infiltration, we observed that muscle involvement began in the posterior calf and progressed to the posterior thigh, pelvis, trunk, anterior thigh, medial thigh, anterior calf, and upper extremity muscles. These muscle clusters correlated significantly with disease duration (τ = 0.47, p < 0.001), 6MWT (τ = -0.49, p < 0.001), and serum creatinine level (τ = -0.46, p < 0.001). The whole-body MRI indicated the thigh as the section most significantly correlated with 6MWT.

INTERPRETATION

We used whole-body muscle MRI to determine the sequential progression of the fat infiltration in SBMA. Our findings may enable the identification of objective and reliable imaging outcome measures in the study of the natural history or future clinical trials of SBMA. ANN NEUROL 2024;95:596-606.

The value of serum creatinine as biomarker of disease progression in spinal and bulbar muscular atrophy (SBMA)

Serum creatinine has been indicated as a potential marker of motor function in SBMA and results form previous longitudinal studies pointed to its decline over time. This is a longitudinal retrospective study investigating creatinine changes over a 36-month-period in 73 patients with SBMA. Severity and progression of the disease was assessed according to serum creatine kinase (CK) values, manual muscle testing (MMT), SBMA functional rating scale (SBMAFRS) score, 6-min-walk test (6MWT) value, and spirometry (forced vital capacity, fVC%) obtained at the baseline and at each of the annual follow-up visits. Baseline serum creatinine concentrations positively correlated with 6MWT, the MMT megascore score of both the upper (ULM) and lower (LLM) limbs and SBMAFRS. No correlation was found with CK or fVC% values. Similar correlation results were achieved at all the subsequent time points. Longitudinal assessments conducted by the generalized estimating equations (GEE) method returned significant changes for SBMAFRS (- 1.41 points per year, p < 0.001), ULM and LLM (- 0.69, p = 0.01; and - 1.07, p < 0.001, respectively), 6MWT (- 47 m, p < 0.001) but not for creatinine (- 0.82, p > 0.05). We also observed that creatinine levels at baseline did not correlate with changes in the other measures from baseline at each annual visit. Our data do not support a role for serum creatinine as sensitive biomarker of disease progression, and possibily prognosis, in SBMA.

Neurodegeneration in the retina of motoneuron diseases: a longitudinal study in amyotrophic lateral sclerosis and Kennedy's disease

BACKGROUND

To what extent retinal atrophy in neurodegenerative diseases reflects the severity and/or the chronicity of brain pathology or is a local independent phenomenon remains to be clarified. Moreover, whether retinal atrophy has a clinical (diagnostic and prognostic) value in these diseases remains unclear.

OBJECTIVE

To add light on the pathological significance and clinical value of retinal atrophy in patients with amyotrophic lateral sclerosis (ALS) and Kennedy's disease (KD).

METHODS

Thirty-five ALS, thirty-seven KD, and forty-nine age-matched healthy controls (HC) were included in a one-year longitudinal study. Spectrum-domain optical coherence tomography (OCT) was performed at study entry (T0) and after 12 months (T1). Disease duration and functional rating scale (FRS) for ALS and KD patients were correlated to retinal thicknesses.

RESULTS

Compared to HC, peripapillary retinal nerve fiber layer (pRNFL) thickness was significantly thinner in both ALS (p = 0.034) and KD (p = 0.003). pRNFL was thinner in KD compared to ALS, but the difference was not significant. In KD, pRNFL atrophy significantly correlated with both disease severity (r = 0.296, p = 0.035) and disease duration (r = - 0.308, p = 0.013) while no significant correlation was found in ALS (disease severity: r = 0.147, p = 0.238; disease duration: r = - 0.093, p = 0.459). During the follow-up, pRNFL thickness remained stable in KD while significantly decreased in ALS (p = 0.043).

CONCLUSIONS

Our study provides evidence of retinal atrophy in both ALS and KD and suggests that retinal thinning is a primary local phenomenon in motoneuron diseases. The clinical value of pRNFL atrophy in KD is worthy of further investigation.

Patients With Becker Muscular Dystrophy Have Severe Paraspinal Muscle Involvement

Introduction: Paraspinal muscles are important for gross motor functions. Impairment of these muscles can lead to poor postural control and ambulation difficulty. Little knowledge exists about the involvement of paraspinal muscles in Becker muscular dystrophy.

Objective: In this cross-sectional study, we investigated the involvement of paraspinal muscles with quantitative trunk strength measure and quantitative muscle MRI.

Methods and Materials: Eighteen patients with Becker muscular dystrophy underwent trunk, hip, and thigh strength assessment using a Biodex dynamometer and an MRI Dixon scan. Fourteen age- and body mass index-matched healthy men were included for comparison.

Results: Muscle fat fraction (FF) of the paraspinal muscles (multifidus and erector spinae) was higher in participants with Becker muscular dystrophy vs. healthy controls at all three examined spinal levels (C6, Th12, and L4/L5) (p < 0.05). There was a strong and inverse correlation between paraspinal muscle FF and trunk extension strength (ρ = −0.829, p < 0.001), gluteus maximus FF and hip extension strength (ρ = −0.701, p = 0.005), FF of the knee extensor muscles (quadriceps and sartorius) and knee extension strength (ρ = −0.842, p < 0.001), and FF of the knee flexor muscles (hamstring muscles) and knee flexion strength (ρ = −0.864, p < 0.001). Fat fraction of the paraspinal muscles also correlated with muscle FF of the thigh muscles and lower leg muscles.

Conclusion: In conclusion, patients with Becker muscular dystrophy demonstrate severe paraspinal muscular involvement indicated by low back extension strength and high levels of fat replacement, which parallel involvement of lower limb muscles. Assessment of paraspinal muscle strength and fat replacement may serve as a possible biomarker for both the clinical management and further study of the disease.

Molecular pathogenesis of spinal bulbar muscular atrophy (Kennedy's disease) and avenues for treatment

PURPOSE OF REVIEW

The aim of this study was to illustrate the current understanding and avenues for developing treatment in spinal and bulbar muscular atrophy (SBMA), an inherited neuromuscular disorder caused by a CAG trinucleotide repeat expansion in the androgen receptor (AR) gene.

RECENT FINDINGS

Important advances have been made in characterizing the molecular mechanism of the disease, including the disruption of protein homeostasis, intracellular trafficking and signalling pathways. Biomarkers such as MRI quantification of muscle volume and fat fraction have been used to track disease progression, and will be useful in future clinical studies. Therapies tested and under development have been based on diverse strategies, including targeting mutant AR gene expression, stability and activity, and pathways that mitigate disease toxicity.

SUMMARY

We provide an overview of the recent advances in understanding the SBMA disease mechanism and highlight efforts to translate these insights into well tolerated and effective therapy.

Quantification of disease progression in spinal muscular atrophy with muscle MRI-a pilot study

OBJECTIVES

Quantitative MRI (qMRI) of muscles is a promising tool to measure disease progression or to assess therapeutic effects in neuromuscular diseases. Longitudinal imaging studies are needed to show sensitivity of qMRI in detecting disease progression in spinal muscular atrophy (SMA). In this pilot study we therefore studied one-year changes in quantitative MR parameters in relation to clinical scores.

METHODS

We repeated quantitative 3 T MR analysis of thigh muscles and clinical testing one year after baseline in 10 treatment-naïve patients with SMA, 5 with Type 2 (21.6 ± 7.0 years) and 5 with Type 3 (33.4 ± 11.9 years). MR protocol consisted of Dixon, T₂ mapping and diffusion tensor imaging (DTI). The temporal relation of parameters was examined with a mixed model.

RESULTS

We detected a significant increase in fat fraction (baseline, 38.2% SE 0.6; follow-up, 39.5% SE 0.6; +1.3%, p = 0.001) in all muscles. Muscles with moderate to high fat infiltration at baseline show a larger increase over time (+1.6%, p < 0.001). We did not find any changes in DTI parameters except for low fat-infiltration muscles (m. adductor longus and m. biceps femoris (short head)). The T₂ of muscles decreased from 28.2 ms to 28.0 ms (p = 0.07). Muscle strength and motor function scores were not significantly different between follow-up and baseline.

CONCLUSION

Longitudinal imaging data show slow disease progression in skeletal muscle of the thigh of (young-) adult patients with SMA despite stable strength and motor function scores. Quantitative muscle imaging demonstrates potential as a biomarker for disease activity and monitoring of therapy response.

MRI in Neuromuscular Diseases: An Emerging Diagnostic Tool and Biomarker for Prognosis and Efficacy

There is an unmet need to identify biomarkers sensitive to change in rare, slowly progressive neuromuscular diseases. Quantitative magnetic resonance imaging (MRI) of muscle may offer this opportunity, as it is noninvasive and can be carried out almost independent of patient cooperation and disease severity. Muscle fat content correlates with muscle function in neuromuscular diseases, and changes in fat content precede changes in function, which suggests that muscle MRI is a strong biomarker candidate to predict prognosis and treatment efficacy. In this paper, we review the evidence suggesting that muscle MRI may be an important biomarker for diagnosis and to monitor change in disease severity. ANN NEUROL 2020;88:669-681.

Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA)

Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular disorder caused by CAG trinucleotide expansion in the gene encoding the androgen receptor (AR). In the central nervous system, lower motor neurons are selectively affected, whereas pathology of patients and animal models also indicates involvement of skeletal muscle including loss of fast-twitch type 2 fibres and increased slow-twitch type 1 fibres, together with a glycolytic-to-oxidative metabolic switch. Evaluation of muscle and fat using MRI, in addition to biochemical indices such as serum creatinine level, are promising biomarkers to track the disease progression. The serum level of creatinine starts to decrease before the onset of muscle weakness, followed by the emergence of hand tremor, a prodromal sign of the disease. Androgen-dependent nuclear accumulation of the polyglutamine-expanded AR is an essential step in the pathogenesis, providing therapeutic opportunities via hormonal manipulation and gene silencing with antisense oligonucleotides. Animal studies also suggest that hyperactivation of Src, alteration of autophagy and a mitochondrial deficit underlie the neuromuscular degeneration in SBMA and provide alternative therapeutic targets.

Contractile properties are impaired in congenital myopathies

The ratio between muscle strength and muscle cross-sectional area is called the specific force. Fatty replacement of muscles is seen in many myopathies, affecting the specific force, without necessarily affecting the ability of the remaining muscle fibers to contract. This ability is called the contractility and is the ratio between muscle strength and the lean muscle cross-sectional area, i.e. the contractile cross-sectional area. We hypothesized that contractility is disrupted in patients with congenital myopathy, because of defects in contractile proteins of the sarcomere. Peak torque across ankle and knee joints was measured by isokinetic dynamometry in 16 patients with congenital myopathy and 13 healthy controls. Five patients only participated partially in the dynamometer measurements due to severe muscle weakness. Dixon MRI technique was used to quantify muscle fat fractions and calculate cross-sectional area. Patients with congenital myopathy had lower cross-sectional area in all muscle groups (P<0.01), higher fat fraction (P<0.01) and less strength (P<0.005) in all studied muscle groups. Their fat content was more than doubled and peak torque lower than half that in healthy controls. Muscle contractility was reduced (P<0.01) in three of four patient muscle groups. In conclusion, muscle contractility was reduced in patients with congenital myopathy, across different diagnoses, and was independent of the level of muscle fat fraction, suggesting that intrinsic defects of the myocyte are responsible for reduced contractility.

A quantitative method to assess muscle edema using short TI inversion recovery MRI

Muscle inflammation is an important component of disease pathophysiology in several muscular dystrophies. Hyperintensities on MRI sequences with short TI inversion recovery (STIR) reflect edema, or inflammation (STIR+). Conventionally, STIR evaluation has been done by visual inspection. In this study, we developed a quantitative STIR method, and tested its ability to identify STIR+ lesions in healthy controls and patients with Facioscapulohumeral muscular dystrophy and compared the results with visual STIR evaluation and quantitative T2 relaxation time mapping. The method was based on pixel-by-pixel histograms of the distribution of signal intensities from muscles. Signal intensities from healthy control muscles were averaged and used to define an upper reference limit. Muscles with >2.5% pixels above the limit were defined as being STIR+. The new method showed agreement with T2 relaxation time mapping in 95% of muscles. The visual STIR method only showed agreement with the quantitative STIR method and T2 relaxation time mapping in 88 and 84%, respectively. STIR sequences are available on most MR scanners and the post-processing used in the new quantitative method can be performed using free software. We therefore believe that the new method can play an important role in identifying STIR+ lesions in patients with neuromuscular diseases.

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.

Skeletal muscle MRI differentiates SBMA and ALS and correlates with disease severity

OBJECTIVE

To investigate the use of muscle MRI for the differential diagnosis and as a disease progression biomarker for 2 major forms of motor neuron disorders: spinal bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS).

METHODS

We applied quantitative 3-point Dixon and semiquantitative T1-weighted and short tau inversion recovery (STIR) imaging to bulbar and lower limb muscles and performed clinical and functional assessments in ALS (n = 21) and SBMA (n = 21), alongside healthy controls (n = 16). Acquired images were analyzed for the presence of fat infiltration or edema as well as specific patterns of muscle involvement. Quantitative MRI measurements were correlated with clinical measures of disease severity in ALS and SBMA.

RESULTS

Quantitative imaging revealed significant fat infiltration in bulbar (p < 0.001) and limb muscles in SBMA compared to controls (thigh: p < 0.001; calf: p = 0.001), identifying a characteristic pattern of muscle involvement. In ALS, semiquantitative STIR imaging detected marked hyperintensities in lower limb muscles, distinguishing ALS from SBMA and controls. Finally, MRI measurements correlated significantly with clinical scales of disease severity in both ALS and SBMA.

CONCLUSIONS

Our findings show that muscle MRI differentiates between SBMA and ALS and correlates with disease severity, supporting its use as a diagnostic tool and biomarker for disease progression. This highlights the clinical utility of muscle MRI in motor neuron disorders and contributes to establish objective outcome measures, which is crucial for the development of new drugs.