Imaging of respiratory muscles in neuromuscular disease: A review

The European reference network for metabolic diseases (MetabERN) clinical pathway recommendations for Pompe disease (acid maltase deficiency, glycogen storage disease type II)

Clinical pathway recommendations (CPR) are based on existing guidelines and deliver a short overview on how to deal with a specific diagnosis, resulting therapy and follow-up. In this paper we propose a methodology for developing CPRs for Pompe disease, a metabolic myopathy caused by deficiency of lysosomal acid alpha-glucosidase. The CPR document was developed within the activities of the MetabERN, a non-profit European Reference Network for Metabolic Diseases established by the European Union. A working group was selected among members of the MetabERN lysosomal storage disease subnetwork, with specific expertise in the care of Pompe disease, and patient support group representatives. The working strategy was based on a systematic literature search to develop a database, followed by quality assessment of the studies selected from the literature, and by the development of the CPR document according to a matrix provided by MetabERN. Quality assessment of the literature and collection of citations was conducted according to the AGREE II criteria and Grading of Recommendations, Assessment, Development and Evaluation methodology. General aspects were addressed in the document, including pathophysiology, genetics, frequency, classification, manifestations and clinical approach, laboratory diagnosis and multidisciplinary evaluation, therapy and supportive measures, follow-up, monitoring, and pregnancy. The CPR document that was developed was intended to be a concise and easy-to-use tool for standardization of care for patients among the healthcare providers that are members of the network or are involved in the care for Pompe disease patients.

Biomarkers in 5q-associated spinal muscular atrophy-a narrative review

5q-associated spinal muscular atrophy (SMA) is a rare genetic disease caused by mutations in the SMN1 gene, resulting in a loss of functional SMN protein and consecutive degeneration of motor neurons in the ventral horn. The disease is clinically characterized by proximal paralysis and secondary skeletal muscle atrophy. New disease-modifying drugs driving SMN gene expression have been developed in the past decade and have revolutionized SMA treatment. The rise of treatment options led to a concomitant need of biomarkers for therapeutic guidance and an improved disease monitoring. Intensive efforts have been undertaken to develop suitable markers, and numerous candidate biomarkers for diagnostic, prognostic, and predictive values have been identified. The most promising markers include appliance-based measures such as electrophysiological and imaging-based indices as well as molecular markers including SMN-related proteins and markers of neurodegeneration and skeletal muscle integrity. However, none of the proposed biomarkers have been validated for the clinical routine yet. In this narrative review, we discuss the most promising candidate biomarkers for SMA and expand the discussion by addressing the largely unfolded potential of muscle integrity markers, especially in the context of upcoming muscle-targeting therapies. While the discussed candidate biomarkers hold potential as either diagnostic (e.g., SMN-related biomarkers), prognostic (e.g., markers of neurodegeneration, imaging-based markers), predictive (e.g., electrophysiological markers) or response markers (e.g., muscle integrity markers), no single measure seems to be suitable to cover all biomarker categories. Hence, a combination of different biomarkers and clinical assessments appears to be the most expedient solution at the time.

Association of diaphragm thickness and density measured on chest CT with disease severity in COVID-19 patients

Introduction

A decrease in muscle mass of the diaphragm could be a significant risk factor for pneumonia. The aim of our study was to evaluate whether diaphragm thickness (DT) and density measured on chest computed tomography (CT) were associated with clinical course and mortality in adult patients with coronavirus disease 2019 (COVID-19) in emergency department admission.

Methods

We retrospectively analyzed 404 patients with a positive polymerase chain reaction test for COVID-19 and pneumonia findings on chest CT between September 1 and November 1, 2020. Bilateral DT measurements were performed at the level of the celiac artery origin, and the total mean diaphragm thickness (TMDT) was estimated. Hemidiaphragm density was measured at the level of the celiac artery origin. The relationship between demographic characteristics, comorbidities, TMDT, mean hemidiaphragm density (MHD) and clinical outcomes was investigated using the logistic regression analyses. The reliability of the measurement of the two observers was evaluated by intraclass correlation analyses.

Results

Intraclass correlation analyses demonstrated almost perfect inter-observer agreement for TMDT and substantial agreement for MHD. There was a statistically significant relationship between the presence of a thinner diaphragm and mortality (p < 0.001). Bilateral diaphragm densities were lower in the patients with severe disease and mortality (p < 0.001). The threshold values of TMDT were 3.67 mm and 3.47 mm for the prediction of ICU admission and mortality, respectively. TMDT (odds ratio [OR]: 0.634, 95% confidence interval [CI]: 0.447–0.901), age (OR: 1.053, 95% CI: 1.027–1.081) and MHD (OR: 0.920, 95% CI: 0.883–0.959) were found to be independent predictors for severe disease in the multivariable model. In addition, MHD (OR: 0.883, 95% CI: 0.827–0.942) and age (OR: 1.040, 95% CI: 1.003–1.078) were independent risk factors for mortality.

Conclusion

Our study demonstrated that a low diaphragm thickness and density measured on chest CT were associated with severe disease in patients with COVID-19 and could be evaluated as poor prognostic markers.

Prevalence of Diaphragmatic Dysfunction in the Long-Term Acute Care Setting and Its Effects on Ventilator Weaning Outcomes: A Retrospective Cohort Study

OBJECTIVE

To determine the prevalence of undiagnosed diaphragmatic dysfunction in a long-term acute care hospital setting in patients on prolonged mechanical ventilation and its association with weaning outcomes.

DESIGN

This is a single-center, retrospective cohort study including 451 patients on prolonged mechanical ventilation admitted to a long-term acute care hospital facility between 2012 and 2017. Diaphragmatic dysfunction was assessed using fluoroscopy.

RESULTS

Three hundred nineteen patients on prolonged mechanical ventilation were assessed for diaphragmatic dysfunction. Nine patients were diagnosed with diaphragmatic dysfunction before admission. Eighty (72.7%) without diaphragmatic dysfunction were successfully weaned and 30 (27.3%) failed to wean, whereas 51 participants (31.9%) with diaphragmatic dysfunction were successfully weaned and 109 (68.1%) failed to wean (P < 0.001). When analyzing days to wean, the median was 13 days for those with no diaphragmatic dysfunction, 19 days with unilateral diaphragmatic dysfunction, and 28 days with bilateral diaphragmatic dysfunction (P < 0.001). Weaning success was not statistically associated with generalized neuromuscular disorders, age, sex, body mass index, smoking history, or diabetes.

CONCLUSIONS

Diaphragmatic dysfunction was found to be strongly associated with time to wean and weaning success in the long-term acute care hospital setting. Very few patients despite being on prolonged mechanical ventilation were diagnosed with diaphragmatic dysfunction before long-term acute care hospital admission. Given this information, early diagnosis of diaphragmatic dysfunction among prolonged mechanical ventilation patients in the long-term acute care hospital setting is paramount in preventing secondary complications associated with mechanical ventilation.

Affection of Respiratory Muscles in ALS and SMA

Respiratory dysfunction is a common cause of morbidity and mortality in motor neuron disease (MND). However, classical volitional measures of respiratory function in these patients are impeded by, e.g., bulbar paralysis or progressive disability. Diaphragm ultrasound imaging might be a valuable tool for assessing respiratory impairment, albeit different ultrasound measures have not been systematically investigated in adult MND patients and, in particular, have not yet been comparatively applied in adult patients with amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). We hypothesized that in contrast to ALS patients, adult SMA patients show a relative sparing of diaphragm function. We retrospectively analyzed diaphragm ultrasound imaging data of 40 patients with ALS and 23 patients with SMA in comparison to a multitude of established parameters of respiratory function. Indeed, ALS patients showed more severe diaphragm dysfunction than adult SMA patients, however, diaphragm dysfunction was also common in adult SMA patients. Notably, dynamic measures of diaphragm function rather than thickness measures were impaired in ALS compared to SMA. Thus, diaphragm ultrasound imaging might be a useful tool to evaluate respiratory dysfunction in adult MND patients. Future larger and prospective studies are needed to validate our initial findings.

Diaphragmatic dysfunction in neuromuscular disease, an MRI study

The aim of this exploratory study was to evaluate diaphragmatic function across various neuromuscular diseases using spirometry-controlled MRI. We measured motion of the diaphragm relative to that of the thoracic wall (cranial-caudal ratio vs. anterior posterior ratio; CC-AP ratio), and changes in the diaphragmatic curvature (diaphragm height and area ratio) during inspiration in 12 adults with a neuromuscular disease having signs of respiratory muscle weakness, 18 healthy controls, and 35 adult Pompe patients - a group with prominent diaphragmatic weakness. CC-AP ratio was lower in patients with myopathies (n=7, 1.25±0.30) and motor neuron diseases (n=5, 1.30±0.10) than in healthy controls (1.37±0.14; p=0.001 and p=0.008), but not as abnormal as in Pompe patients (1.12±0.18; p=0.011 and p=0.024). The mean diaphragm height ratio was 1.17±0.33 in patients with myopathies, pointing at an insufficient diaphragmatic contraction. This was also seen in patients with Pompe disease (1.28±0.36), but not in healthy controls (0.82±0.33) or patients with motor neuron disease (0.82±0.24). We conclude that spirometry-controlled MRI enables us to investigate respiratory dysfunction across neuromuscular diseases, suggesting that the diaphragm is affected in a different way in myopathies and motor neuron diseases. Whether MRI can also be used to evaluate progression of diaphragmatic dysfunction requires additional studies.

European Respiratory Society statement on thoracic ultrasound

Thoracic ultrasound is increasingly considered to be an essential tool for the pulmonologist. It is used in diverse clinical scenarios, including as an adjunct to clinical decision making for diagnosis, a real-time guide to procedures and a predictor or measurement of treatment response. The aim of this European Respiratory Society task force was to produce a statement on thoracic ultrasound for pulmonologists using thoracic ultrasound within the field of respiratory medicine. The multidisciplinary panel performed a review of the literature, addressing major areas of thoracic ultrasound practice and application. The selected major areas include equipment and technique, assessment of the chest wall, parietal pleura, pleural effusion, pneumothorax, interstitial syndrome, lung consolidation, diaphragm assessment, intervention guidance, training and the patient perspective. Despite the growing evidence supporting the use of thoracic ultrasound, the published literature still contains a paucity of data in some important fields. Key research questions for each of the major areas were identified, which serve to facilitate future multicentre collaborations and research to further consolidate an evidence-based use of thoracic ultrasound, for the benefit of the many patients being exposed to clinicians using thoracic ultrasound.

Correlation Between Respiratory Accessory Muscles and Diaphragm Pillars MRI and Pulmonary Function Test in Late-Onset Pompe Disease Patients

Objectives: Pompe disease is a rare genetic disease produced by mutations in the GAA gene leading to progressive skeletal and respiratory muscle weakness. T1-weighted magnetic resonance imaging is useful to identify fatty replacement in skeletal muscles of late-onset Pompe disease (LOPD) patients. Previous studies have shown that replacement by fat correlates with worse results of muscle function tests. Our aim was to investigate if fat replacement of muscles involved in the ventilation process correlated with results of the spirometry and predicted respiratory muscle impairment in LOPD patients over time.

Materials and Methods: We studied a cohort of 36 LOPD patients followed up annually in our center for a period of 4 years. We quantified muscle fat replacement using Mercuri score of the thoracic paraspinal and abdominal muscles and the pillars of the diaphragm. We correlated the combined Mercuri scores of these areas with spirometry results and the need of respiratory support.

Results: We found a statistically significant correlation (Spearman test, p < 0.05; coefficient of correlation > 0.6) between forced vital capacity seated and lying and fat fraction score of all muscle groups studied. The group of patients who needed respiratory support had higher fat fraction scores than patients not requiring ventilatory support. Higher fat replacement in these areas correlated with worse progression in spirometry values over time.

Conclusions: Fat replacement of paraspinal, abdominal, and trunk muscles correlates with results of spirometry and is able to predict worsening in respiratory muscle function tests that could lead to an emerging ventilatory dysfunction. Therefore, the identification of fat replacement in these muscle groups should lead to a closer monitorization of patients. Radiologic evaluation of diaphragm pillars in T1-weighted imaging axial sequences could also be helpful to predict respiratory insufficiency.

Diaphragmatic dysfunction at the first visit to a chest diseases outpatient clinic in 500 patients with amyotrophic lateral sclerosis

INTRODUCTION

In this study, we aimed to evaluate diaphragmatic dysfunction (DD) by using a practical approach in patients with amyotrophic lateral sclerosis (ALS) at the first visit to a chest diseases outpatient clinic.

METHODS

Patients with ALS seen in our outpatient clinic for the past 5 y and followed up for at least 1 y, were retrospectively evaluated. Having at least one of the following three criteria was accepted as DD: (a) paradoxical abdominal movement (PAM), (b) sitting-supine forced vital capacity (FVC) difference ≥ 20%, (c) sitting-supine arterial oxygen saturation measured by pulse oximetry (SpO₂ ) difference ≥ 4%. Respiratory symptoms, arterial blood gas analysis, sleep studies, noninvasive mechanical ventilation use, and mortality were recorded.

RESULTS

Five-hundred patients with ALS were included (female/male: 220/280, age: 58.9 ± 11.3 y). Of the patients, 22.8% had daytime hypercapnia. DD was observed in 55% of the patients (PAM in 112, sitting-supine FVC difference ≥ 20% in 50, and sitting-supine SpO₂ difference ≥ 4% in 113 patients). Of the patients with DD, 31.6% (n = 87) had no respiratory symptoms, 46.4% had FVC > 70% and 33.5% had FVC <50%. Nocturnal hypoxemia (sleep time spent with SpO₂  < 90% ≥30%) was present in 59.7%, and all patients with nocturnal hypoxemia had DD. Obstructive sleep apnea (8 severe, 14 moderate, 39 mild) was detected in 55% of the patients with polysomnography (n = 61) or polygraphy (n = 50). During follow-up, 52.2% of the patients died. Mean survival time was shorter in patients with DD (P < .001).

CONCLUSION

Paradoxical abdomimal movement (PAM), sitting-supine SpO₂ difference ≥ 4% and sitting-supine FVC difference ≥ 20% are indicators of DD, which should be routinely evaluated at every outpatient visit.

Chest MRI to diagnose early diaphragmatic weakness in Pompe disease

Background

In Pompe disease, an inherited metabolic muscle disorder, severe diaphragmatic weakness often occurs. Enzyme replacement treatment is relatively ineffective for respiratory function, possibly because of irreversible damage to the diaphragm early in the disease course. Mildly impaired diaphragmatic function may not be recognized by spirometry, which is commonly used to study respiratory function. In this cross-sectional study, we aimed to identify early signs of diaphragmatic weakness in Pompe patients using chest MRI.

Methods

Pompe patients covering the spectrum of disease severity, and sex and age matched healthy controls were prospectively included and studied using spirometry-controlled sagittal MR images of both mid-hemidiaphragms during forced inspiration. The motions of the diaphragm and thoracic wall were evaluated by measuring thoracic cranial-caudal and anterior–posterior distance ratios between inspiration and expiration. The diaphragm shape was evaluated by measuring the height of the diaphragm curvature. We used multiple linear regression analysis to compare different groups.

Results

We included 22 Pompe patients with decreased spirometry results (forced vital capacity in supine position < 80% predicted); 13 Pompe patients with normal spirometry results (forced vital capacity in supine position ≥ 80% predicted) and 18 healthy controls. The mean cranial-caudal ratio was only 1.32 in patients with decreased spirometry results, 1.60 in patients with normal spirometry results and 1.72 in healthy controls (p < 0.001). Anterior–posterior ratios showed no significant differences. The mean height ratios of the diaphragm curvature were 1.41 in patients with decreased spirometry results, 1.08 in patients with normal spirometry results and 0.82 in healthy controls (p = 0.001), indicating an increased curvature of the diaphragm during inspiration in Pompe patients.

Conclusions

Even in early-stage Pompe disease, when spirometry results are still within normal range, the motion of the diaphragm is already reduced and the shape is more curved during inspiration. MRI can be used to detect early signs of diaphragmatic weakness in patients with Pompe disease, which might help to select patients for early intervention to prevent possible irreversible damage to the diaphragm.

Ultrasound assessment of diaphragm function in patients with late-onset Pompe disease

INTRODUCTION

Late-Onset Pompe Disease (LOPD) is characterized by progressive limb-girdle muscle weakness and respiratory dysfunction. Diaphragm is the most impaired muscle in LOPD and its dysfunction cause major respiratory symptoms. The aim of this study was to evaluate the correlation between diaphragm thickness and mobility assessed by ultrasonography and respiratory function and muscle strength tests in patients with LOPD.

METHODS

17 patients with LOPD (9 female, 47 ± 15 years) and 17 age and gender-matched healthy controls underwent spirometry, muscle strength testing, and ultrasound evaluation of diaphragm excursion and thickness.

RESULTS

The following parameters were significantly reduced in LOPD patients versus controls (all p < 0.001): forced vital capacity (FVC) in seated and supine position, maximum inspiratory and expiratory pressure (MIP and MEP), diaphragm excursion, thickness at functional residual capacity (FRC) and total lung capacity (TLC), and thickness fraction (TF). Ultrasound studies of diaphragm thickness at FRC correlated with MIP (r = 0.74; p < 0.0001) and seated FVC(r = 0.73; p < 0.05). Diaphragm thickness at TLC correlated with MIP (r = 0.85; p < 0.0001) and FVC in both seated (r = 0.77; p < 0.0001) and supine position (r = 0.68; p < 0.05). TF correlated significantly with MIP (r = 0.80; p < 0.001), FVC in both seated (r = 0.66; p < 0,005) and supine position (r = 0.61; p < 0.05). Interestingly diaphragm thickness at FRC correlated with disease duration (years) in LOPD patients (r = -0.53; p < 0,05). Ultrasound diaphragm mobility correlated with diaphragm thickness at TLC(r = 0.87; p < 0.0001), FRC (r = 0.84; p < 0.005) and TF (r = 0.73; p < 0.05). Moreover diaphragm mobility correlated with FVC in seated(r = 0.79; p < 0.005) and supine position(r = 0.74; p < 0.05) and MIP (r = 0.81; p < 0.005).

CONCLUSION

Diaphragm ultrasonography is a simple and reproducible technique for manage respiratory dysfunction in LOPD patients.

Imaging respiratory muscle quality and function in Duchenne muscular dystrophy

OBJECTIVE

Duchenne muscular dystrophy (DMD) is characterized by damage to muscles including the muscles involved in respiration. Dystrophic muscles become weak and infiltrated with fatty tissue, resulting in progressive respiratory impairment. The objective of this study was to assess respiratory muscle quality and function in DMD using magnetic resonance imaging and to determine the relationship to clinical respiratory function.

METHODS

Individuals with DMD (n = 36) and unaffected controls (n = 12) participated in this cross sectional magnetic resonance imaging study. Participants underwent dynamic imaging of the thorax to assess diaphragm and chest wall mobility and chemical shift-encoded imaging of the chest and abdomen to determine fatty infiltration of the accessory respiratory muscles. Additionally, clinical pulmonary function measures were obtained.

RESULTS

Thoracic cavity area was decreased in individuals with DMD compared to controls during tidal and maximal breathing. Individuals with DMD had reduced chest wall movement in the anterior-posterior direction during maximal inspirations and expirations, but diaphragm descent during maximal inspirations (normalized to height) was only decreased in a subset of individuals with maximal inspiratory pressures less than 60% predicted. Muscle fat fraction was elevated in all three expiratory muscles assessed (p < 0.001), and the degree of fatty infiltration correlated with percent predicted maximal expiratory pressures (r =  - 0.70, p < 0.001). The intercostal muscles demonstrated minimal visible fatty infiltration; however, this analysis was qualitative and resolution limited.

INTERPRETATION

This magnetic resonance imaging investigation of diaphragm movement, chest wall movement, and accessory respiratory muscle fatty infiltration provides new insights into the relationship between disease progression and clinical respiratory function.

ERS statement on respiratory muscle testing at rest and during exercise

Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.

The use of chest magnetic resonance imaging in interstitial lung disease: a systematic review

Thin-slices multi-detector computed tomography (MDCT) plays a key role in the differential diagnosis of interstitial lung disease (ILD). However, thin-slices MDCT has a limited ability to detect active inflammation, which is an important target of newly developed ILD drug therapy. Magnetic resonance imaging (MRI), thanks to its multi-parameter capability, provides better tissue characterisation than thin-slices MDCT.Our aim was to summarise the current status of MRI applications in ILD and to propose an ILD-MRI protocol. A systematic literature search was conducted for relevant studies on chest MRI in patients with ILD.We retrieved 1246 papers of which 55 original papers were selected for the review. We identified 24 studies comparing image quality of thin-slices MDCT and MRI using several MRI sequences. These studies described new MRI sequences to assess ILD parenchymal abnormalities, such as honeycombing, reticulation and ground-glass opacity. Thin-slices MDCT remains superior to MRI for morphological imaging. However, recent studies with ultra-short echo-time MRI showed image quality comparable to thin-slices MDCT. Several studies demonstrated the added value of chest MRI by using functional imaging, especially to detect and quantify inflammatory changes.We concluded that chest MRI could play a role in ILD patients to differentiate inflammatory and fibrotic changes and to assess efficacy of new ILD drugs.

A case of unexplained dyspnoea: when lung function testing matters!

“Lung function corner” articles in Breathe present the results of a lung function test and the authors then debate the interpretation, including potential controversies and background from the literature. As section editors of this newly created section of Breathe, we felt it was important to write the first article, which highlights the usefulness of lung function testing in guiding clinical diagnosis especially in difficult cases such the one we discuss here.

Diverse methods are available for assessment of the respiratory muscles; the technique used should be tailored to the question posed.http://ow.ly/ChbX30m91bt

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.