2022 Workshop Handout Bundle-EDX Approach to Myopathies Needle EMG of Unusual Muscles

EDX Approach to Myopathies Needle EMG of Unusual Muscles

Pdf Summary

The electrodiagnostic approach to myopathies is an important component in the evaluation of patients with suspected muscle disorders. It can help determine the presence and type of myopathy, differentiate between neuropathy and myopathy, identify specific patterns of abnormalities for different myopathies, assess disease activity, guide muscle biopsy selection, and monitor response to treatment. Myopathies can be classified as acquired or hereditary, with acquired myopathies having different underlying mechanisms such as immune-mediated, toxic, metabolic, or infectious causes. Hereditary myopathies have various classifications based on clinical phenotype, weakness distribution, or genetic defects. However, there is significant overlap between different myopathies in terms of phenotype, onset age, and histopathological features, making classification challenging. It is increasingly important to establish a specific genetic diagnosis, especially in the gene-therapy era. <br /><br />When evaluating patients with suspected myopathy, it is crucial to determine the clinical phenotype, as the pattern of weakness can vary. Proximal myopathies are the most common, but other patterns such as distal or axial myopathies are often misdiagnosed or underdiagnosed. There can also be overlap between myopathies and neuropathies or neuromuscular transmission defects, making diagnosis more complex. <br /><br />The electrodiagnostic approach to myopathies involves conducting nerve conduction studies to rule out superimposed peripheral neuropathy and performing needle electromyography (EMG) to assess muscle activity. Specific muscles are targeted based on clinical findings and may include axial muscles that are commonly missed. EMG findings can vary, and the presence or absence of fibrillation potentials and myotonic discharges should be interpreted cautiously, as they can correlate with different histopathological features. A target for muscle biopsy is selected based on EMG findings, avoiding normal or end-stage muscles and opting for moderately severe weakness. Surgeons performing muscle biopsies should be familiar with specific muscle targets, and additional muscles can be sampled if needed. <br /><br />To mitigate the complexity of myopathies, a systematic approach should be followed with a focus on affected muscles, being descriptive, and avoiding forcing findings into specific categories. Suggested readings include articles on pattern recognition in myopathies, muscle biopsy and EMG correlation, axial myopathies, limb-girdle muscular dystrophies, inflammatory myopathies, and inherited distal myopathies.

Keywords

electrodiagnostic approach

myopathies

evaluation

muscle disorders

neuropathy

myopathy differentiation

abnormalities

disease activity assessment

muscle biopsy

treatment response monitoring