2023 Workshop Handout Bundle-Myopathies

Myopathies - EDX Approach

Pdf Summary

The document "Myopathies: An Electrodiagnostic (EDX) Approach" by Dr. Hani Kushlaf outlines the processes and considerations involved in diagnosing myopathies using electrodiagnostic methods. Myopathies are characterized by symptoms such as muscle weakness, hyperCKemia, abnormal lab results, muscle stiffness, pain, rhabdomyolysis, muscle twitching, or atrophy. The clinical exam may reveal specific patterns of weakness, and while electrodiagnostic studies can indicate abnormalities suggestive of myopathy, they cannot specify the type. Muscle biopsy remains necessary for a definitive diagnosis.<br /><br />The electrodiagnostic evaluation involves both nerve conduction studies and needle electromyography. Nerve conduction studies typically show normal sensory responses unless there's an added polyneuropathy. Motor nerve conduction studies are usually normal except in specific myopathies like inclusion body myositis. Critical illness myopathy (CIM) is characterized by prolonged compound muscle action potential (CMAP) duration without the increased temporal dispersion seen in demyelinating neuropathies.<br /><br />Needle electromyography examines multiple muscles due to the selective and patchy nature of myopathic involvement. This includes assessing both spontaneous activity and volitional motor unit action potentials (MUAPs). Sampling weak muscles is crucial to detect myopathic changes. The document emphasizes that decreased MUAP duration—a reliable indicator of myopathy—results from a loss of muscle fibers within the motor unit. Early recruitment, evidenced by minimal muscle activation triggering multiple MUAPs, is another key feature. The document also advises against examining contralateral proximal muscles to preserve them for potential muscle biopsy.<br /><br />Additionally, the text notes specific abnormalities like decreased insertional activity in fibrous or fatty tissue, muscle rippling, and contractures, which are electrically silent. Electrical myotonia without clinical symptoms may point to diagnoses such as colchicine myopathy. The document provides references for further detail on electrodiagnostic findings in different myopathies.<br /><br />In summary, electrodiagnostic studies play a vital role in confirming myopathy, determining its severity, mapping the affected muscle distribution, and selecting biopsy sites, but cannot replace muscle biopsies for definitive diagnosis.

Keywords

myopathies

electrodiagnostic

muscle weakness

nerve conduction studies

ncs

needle electromyography

muscle biopsy

motor unit action potentials

critical illness myopathy

early recruitment

myotonia

nerve conduction studies

nerve conduction study

ncs