2023 Workshop Handout Bundle-EDX Approach to Myopathies Needle EMG of Unusual Muscles

EDX Approach to Myopathies Needle EMG of Unusual Muscles

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The document "EDX Approach to Myopathies: Needle EMG of Unusual Muscles" by Dr. Elie Naddaf from the Mayo Clinic discusses the electrodiagnostic (EDX) approach to evaluating myopathies, a group of muscle diseases. Myopathies can be divided into acquired (immune-mediated, toxic, metabolic, or infectious) and hereditary categories. Advances in genetic testing have revealed significant overlaps in clinical phenotypes, age of onset, and histopathological findings, leading to redefining classifications based on specific genetic mutations, e.g., RYR1 myopathy or titinopathy.<br /><br />The primary step in EDX evaluation is determining the clinical phenotype, as myopathies can affect any skeletal muscle and present in diverse patterns (diffuse, proximal, distal, etc.). Diagnosing axial myopathies, which affect muscles responsible for posture and vital functions like breathing, often requires careful EDX testing of axial muscles due to common underdiagnosis and sampling errors.<br /><br />Overlap presentations between myopathies and conditions like neuropathies or neuromuscular transmission (NMT) defects complicate diagnosis. Routine nerve conduction studies typically rule out superimposed processes, while needle electromyography (EMG) is essential for detecting myopathic changes by assessing motor unit potentials, fibrillation potentials, and myotonic discharges. Identifying specific patterns helps in muscle biopsy selection.<br /><br />The report emphasizes a standardized, systematic approach to EDX testing, including sampling clinically affected muscles and interpreting EMG findings cautiously. While severe muscle weakness might show decreased insertional activity, the presence of fibrillation potentials indicates active or chronic muscle changes, but not necessarily ongoing inflammation. Muscle biopsy should target weak but not end-stage muscles, and sampling should be performed cautiously, possibly involving muscle imaging for better accuracy.<br /><br />The document advocates for a descriptive approach in EMG reporting, avoiding over-fitting findings into predefined categories, thus enhancing diagnostic accuracy and patient care. References include studies on muscle biopsy-EMG correlation, axial myopathies, and classification of inflammatory myopathies.

Keywords

myopathies

electrodiagnostic

needle EMG

genetic testing

RYR1 myopathy

titinopathy

axial muscles

neuropathy

muscle biopsy

Mayo Clinic