2025 Workshop Handout Bundle-W55B EDX Approach to Myopathies

W55B EDX Approach to Myopathies - Naddaf

Pdf Summary

This document, presented by Dr. Elie Naddaf, discusses the electrodiagnostic (EDX) approach, especially needle electromyography (EMG), in evaluating patients with suspected myopathies—muscle diseases characterized by weakness. EDX is vital for confirming myopathy presence, differentiating it from neuropathies, identifying specific types, assessing disease activity, guiding muscle biopsy, and monitoring treatment effects.<br /><br />Myopathies are broadly classified as acquired or hereditary. Acquired types arise from immune, toxic, metabolic, or infectious causes. Hereditary myopathies include muscular dystrophies (e.g., Duchenne, myotonic dystrophy type 1, and facioscapulohumeral dystrophy) notable for rapid progression and fiber loss, and congenital myopathies characterized by slow progression and distinct pathology. Modern genetic testing shows substantial phenotypic overlap among myopathies, emphasizing the need for gene-based diagnoses (e.g., titinopathy, RYR1 myopathy).<br /><br />Clinical phenotype assessment is crucial, focusing on the pattern of muscle weakness—diffuse, proximal, distal, axial, or involving specific muscle groups—which guides EMG targeting. Axial myopathies and distal myopathies are often underdiagnosed. Overlapping conditions with neuropathies or neuromuscular transmission defects complicate the picture.<br /><br />The EDX workup includes routine nerve conduction studies to exclude neuropathy and needle EMG targeting clinically affected muscles, including less commonly tested axial muscles (thoracic paraspinals, infraspinatus, pectoralis major). Needle EMG findings like fibrillation potentials and myotonic discharges provide clues but must be interpreted cautiously as they overlap among different myopathies and may not always reflect active inflammation.<br /><br />Selecting an appropriate muscle for biopsy relies on clinical and EMG data, avoiding end-stage or normal-strength muscles. The preferred biopsy sites include the vastus lateralis, deltoid, biceps, or triceps, with more specialized muscles requiring expert surgeons.<br /><br />To improve diagnostic yield, practitioners should adopt a systematic approach focusing on affected muscles, sampling multiple muscles when uncertain, and avoiding forcing results into rigid categories given the complexity and overlap in myopathic presentations. Comprehensive reporting assists referring physicians in management.<br /><br />Key references provide further reading on myopathy patterns, diagnosis, and management.

Keywords

Electrodiagnostic approach

Needle electromyography

Myopathies

Muscle weakness

Genetic testing

Muscle biopsy

Nerve conduction studies

ncs

Axial myopathies

Distal myopathies

Neuromuscular diagnosis