Ultrasound in ALS: is it a sound method?

Muscle ultrasound: Present state and future opportunities

Muscle ultrasound is a valuable addition to the neuromuscular toolkit in both the clinic and research settings, with proven value and reliability. However, it is currently not fulfilling its full potential in the diagnostic care of patients with neuromuscular disease. This review highlights the possibilities and pitfalls of muscle ultrasound as a diagnostic tool and biomarker, and discusses challenges to its widespread implementation. We expect that limitations in visual image interpretation, posed by user inexperience, could be overcome with simpler scoring systems and the help of deep-learning algorithms. In addition, more information should be collected on the relation between specific neuromuscular disorders, disease stages, and expected ultrasound abnormalities, as this will enhance specificity of the technique and enable the use of muscle ultrasound as a biomarker. Quantified muscle ultrasound gives the most sensitive results but is hampered by the need for device-specific reference values. Efforts in creating dedicated muscle ultrasound systems and artificial intelligence to help with image interpretation are expected to improve usability. Finally, the standard inclusion of muscle and nerve ultrasound in neuromuscular teaching curricula and guidelines will facilitate further implementation in practice. Our hope is that this review will help in unleashing muscle ultrasound's full potential.

Biomarkers and the Development of a Personalized Medicine Approach in Spinal Muscular Atrophy

Recent unprecedented advances in treatment for spinal muscular atrophy (SMA) enabled patients to access the first approved disease modifying therapy for the condition. There are however many uncertainties, regarding timing of treatment initiation, response to intervention, treatment effects and long-term outcomes, which are complicated by the evolving phenotypes seen in the post-treatment era for patients with SMA. Biomarkers of disease, with diagnostic, prognostic, predictive, and pharmacodynamic value are thus urgently required, to facilitate a wider understanding in this dynamic landscape. A spectrum of these candidate biomarkers, will be evaluated in this review, including genetic, epigenetic, proteomic, electrophysiological, and imaging measures. Of these, SMN2 appears to be the most significant modifier of phenotype to date, and its use in prognostication shows considerable clinical utility. Longitudinal studies in patients with SMA highlight an emerging role of circulatory markers such as neurofilament, in tracking disease progression and response to treatment. Furthermore, neurophysiological biomarkers such as CMAP and MUNE values show considerable promise in the real word setting, in following the dynamic response and output of the motor unit to therapeutic intervention. The specific value for these possible biomarkers across diagnosis, prognosis, prediction of treatment response, efficacy, and safety will be central to guide future patient-targeted treatments, the design of clinical trials, and understanding of the pathophysiological mechanisms of disease and intervention.

Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is characterised by the progressive loss of motor neurons in the brain and spinal cord. This neurodegenerative syndrome shares pathobiological features with frontotemporal dementia and, indeed, many patients show features of both diseases. Many different genes and pathophysiological processes contribute to the disease, and it will be necessary to understand this heterogeneity to find effective treatments. In this Seminar, we discuss clinical and diagnostic approaches as well as scientific advances in the research fields of genetics, disease modelling, biomarkers, and therapeutic strategies.

Assessment of Motor Units in Neuromuscular Disease

The motor unit comprises the anterior horn cell, its axon, and the muscle fibers that it innervates. Although the true number of motor units is unknown, the number of motor units appears to vary greatly between different muscles and between different individuals. Assessment of the number and function of motor units is needed in diseases of the anterior horn cell and other motor nerve disorders. Amyotrophic lateral sclerosis is the most important disease of anterior horn cells. The need for an effective biomarker for assessing disease progression and for use in clinical trials in amyotrophic lateral sclerosis has stimulated the study of methods to measure the number of motor units. Since 1970 a number of different methods, including the incremental, F-wave, multipoint, and statistical methods, have been developed but none has achieved widespread applicability. Two methods (MUNIX and the multipoint incremental method) are in current use across multiple centres and are discussed in detail in this review, together with other recently published methods. Imaging with magnetic resonance and ultrasound is increasingly being applied to this area. Motor unit number estimates have also been applied to other neuromuscular diseases such as spinal muscular atrophy, compression neuropathies, and prior poliomyelitis. The need for an objective measure for the assessment of motor units remains tantalizingly close but unfulfilled in 2016.