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["Fatiguability" in myasthenic syndromes].
Fortschritte Der Neurologie, Psychiatrie, Und Ihrer Grenzgebiete
|June 1, 1975
Summary
Myasthenic syndromes exhibit abnormal muscle fatigability on electromyograms, distinct from myasthenia gravis. This fatigability may stem from reduced intact muscle fibers rather than neuromuscular transmission failure.
Area of Science:
- Neurology
- Clinical Electrophysiology
Context:
- Myasthenic syndromes present with a
- myasthenic reaction
- but lack other myasthenia gravis symptoms and do not respond to cholinergic drugs.
- Abnormal muscle fatigability is a key characteristic, detectable via electromyography (EMG).
Purpose:
- To differentiate myasthenic syndromes from myasthenia gravis.
- To explore the underlying mechanisms of abnormal fatigability in myasthenic syndromes.
- To investigate the role of neuromuscular transmission versus muscle fiber integrity.
Summary:
- Neuromuscular disorders with a myasthenic reaction but no response to cholinergic drugs are termed myasthenic syndromes.
- Electromyography reveals abnormal fatigability, characterized by EMG pattern rarefication during sustained contraction or decreased muscle potential amplitude during repetitive nerve stimulation.
- This decrease is poorly affected by cholinergic drugs, observed in myositis, myotonic dystrophy, other myopathies, and rarely, neurogenic disorders.
Impact:
- Challenges the sole explanation of neuromuscular transmission failure in myasthenic syndromes.
- Proposes reduced intact muscle fibers leading to rapid muscle fiber fatigue as a potential alternative mechanism.
- Highlights the importance of investigating abnormal fatigability in diagnosing and understanding myasthenic syndromes.