2025 Workshop Handout Bundle-W55C Myopathies EDX Approach

W55C Myopathies EDX Approach - Kushlaf

Pdf Summary

This presentation by Dr. Hani Kushlaf outlines the electrodiagnostic (EDX) approach to diagnosing myopathies. Patients referred for EDX evaluation present with symptoms such as muscle weakness (proximal, distal, or axial), increased creatine kinase (CK) levels, muscle pain, stiffness, twitching, atrophy, or abnormal lab markers. The EDX study helps confirm myopathy, determine its severity and muscle involvement, and guide muscle biopsy selection but does not on its own provide a definitive diagnosis for specific myopathies (e.g., inclusion body myositis requires biopsy confirmation).<br /><br />The EDX evaluation typically starts with nerve conduction studies (NCS). Sensory NCS are usually normal unless a neuropathy is present. Motor NCS are also often normal except in distal myopathies or conditions like critical illness myopathy (CIM), where compound muscle action potential (CMAP) duration is prolonged without temporal dispersion, reflecting muscle fiber membrane changes.<br /><br />Needle electromyography (EMG) examines selected muscles based on clinical weakness and symptom distribution. Sampling multiple muscles, including thoracic paraspinals, is recommended due to patchy involvement. EMG evaluates spontaneous activity (e.g., fibrillations, positive sharp waves) and motor unit action potentials (MUAPs). Myopathies typically show decreased MUAP duration and early recruitment patterns. Chronic myopathies may also show reinnervation signs complicating interpretation. Certain patterns, such as electrical myotonia without clinical myotonia, suggest specific diagnoses like colchicine myopathy. Differentiating myopathy from presynaptic neuromuscular junction disorders requires combining clinical and electrodiagnostic findings, including repetitive nerve stimulation tests.<br /><br />The presentation emphasizes tailoring the electrodiagnostic study to the patient’s clinical presentation and carefully selecting muscles for examination and biopsy. It highlights the importance of interpreting findings in context and the necessity of muscle biopsy and other tests for definitive diagnosis.<br /><br />References cited include standard guidelines on EMG/NCS techniques and discussions on electrodiagnostic findings in myopathies and critical illness myopathy.

Keywords

Electrodiagnostic evaluation

Myopathy diagnosis

Muscle weakness

Creatine kinase elevation

Nerve conduction studies

ncs

Needle electromyography

Motor unit action potentials

Muscle biopsy selection

Critical illness myopathy

Electrical myotonia