Abstract
Introduction: In myopathies, the correlation of individual electromyographic and histopathologic findings remains poorly explored, as most previous studies have focused on the ability of muscle biopsy and electromyography to distinguish the neuropathic vs. myopathic nature of the underlying neuromuscular disease.Methods: We identified 100 patients who had a muscle biopsy and electromyography performed on identical muscles. We used a detailed grading system ranging from 0- normal to 4- severe; and graded 16 histopathologic findings in each biopsy. Electromyography findings were also graded from 0 to 4 according to the standard protocol in our EMG laboratory. We used Kendall's tau for non-parametric ordinal correlation analysis.Results: Fibrillation potentials correlated with atrophic, necrotic, and regenerating fibers, fibers harboring vacuoles, fiber splitting, fibers reacting for non-specific esterase, fibers with congophilic inclusions, inflammation (endoymysial and perimysial), and increased endomysial connective tissue. Short-duration motor unit potentials correlated with atrophic, necrotic, and regenerating fibers, increased endomysial connective tissue, and perimysial inflammation. Long-duration motor unit potentials correlated with fiber-type grouping. Increased phases of motor unit potentials correlated with atrophic fibers, increased endomysial connective tissue, and fibers reacting for non-specific esterase; while increased turns correlated with atrophic and regenerating fibers, increased endomysial connective tissue and target formations. Rapid recruitment correlated with regenerating fibers, perimysial inflammation, and increased endomysial connective tissue.Discussion: By demonstrating a clear correlation of various electromyographic and histopathologic findings, this study improves interpreting electrodiagnostic testing in myopathies, and serves as the basis to further assess the correlation between clinical, electromyographic, and histopathologic findings.
Highlights
In myopathies, the correlation of individual electromyographic and histopathologic findings remains poorly explored, as most previous studies have focused on the ability of muscle biopsy and electromyography to distinguish the neuropathic vs. myopathic nature of the underlying neuromuscular disease
Per our Muscle laboratory protocol, muscle biopsy specimens were frozen in isopentane-cooled in liquid nitrogen with serial 10 μm sections stained with hematoxylin-eosin, trichrome, nicotinamide adenine dinucleotide dehydrogenase (NADH), succinate dehydrogenase (SDH), cytochrome c oxidase (CCO), ATPase, acid phosphatase, myophosphorylase, periodic acid-Schiff (PAS), oil-red O, non-specific esterase (NSE), and Congo red
It is not uncommon to have more than one histopathologic diagnosis revealed by a single muscle biopsy, only the predominant finding is listed in the figure
Summary
The correlation of individual electromyographic and histopathologic findings remains poorly explored, as most previous studies have focused on the ability of muscle biopsy and electromyography to distinguish the neuropathic vs. myopathic nature of the underlying neuromuscular disease. Electrodiagnostic testing is a cardinal component of the evaluation of patients with suspected myopathy [1] It can help identify an ongoing myopathy, differentiating a neuropathy from a myopathy, recognizing a pattern of abnormalities that can point to a specific myopathy, determining disease activity, selecting the appropriate muscle for biopsy, and assessing response to or side effects of a pharmacological treatment. One essential EMG element clinicians rely on in their diagnostic approach is presence or absence of abnormal spontaneous discharges such as fibrillation potentials, myotonic discharges, or complex repetitive discharges [2]. These findings can be associated with a wide spectrum of neuromuscular disorders encompassing neuropathic and myopathic disorders. In different electrodiagnostic laboratories, the presence of fibrillation potentials may be interpreted in different ways and as a correlate of: membrane instability, active myopathy, inflammation or denervation
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