Myotonic Discharges in Anti-MuSK Myasthenia

Joundi, Raed A.; Israelian, G.; Ghavanini, Amer A.; Kassardjian, Charles D.

doi:10.1017/cjn.2018.318

Cited by 4 publications

(5 citation statements)

References 8 publications

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“…Myotonic discharges can also be found in other neuromuscular disorders such as Pompe disease (often isolated discharges in paraspinal muscles 80 ), inflammatory myopathy, congenital myopathy (especially myofibrillar myopathy 81 ), rippling muscle disease, 82 and anti‐MuSK myasthenia gravis (for complete overview see Hehir and Logigian 83 ). 84 …”

Section: Diagnosismentioning

confidence: 99%

Guidelines on clinical presentation and management of nondystrophic myotonias

et al. 2020

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The nondystrophic myotonias are rare muscle hyperexcitability disorders caused by gain-of-function mutations in the SCN4A gene or loss-of-function mutations in the CLCN1 gene. Clinically, they are characterized by myotonia, defined as delayed muscle relaxation after voluntary contraction, which leads to symptoms of muscle stiffness, pain, fatigue, and weakness. Diagnosis is based on history and examination findings, the presence of electrical myotonia on electromyography, and genetic confirmation. In the absence of genetic confirmation, the diagnosis is supported by detailed electrophysiological testing, exclusion of other related disorders, and analysis of a variant of uncertain significance if present.

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Section: Diagnosismentioning

confidence: 99%

Guidelines on clinical presentation and management of nondystrophic myotonias

et al. 2020

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“…SCN4A variants can cause both CMS and myotonia 9 , but myotonia has never been documented in CMS arising from AChR deficiency or, specifically, CHRNE variants. Autoimmune myasthenia gravis was associated with myotonia in one case of anti-MuSK antibodies 10 , but it is rare for CMS to coexist with autoimmune myasthenia gravis, and our patient was seronegative. Myotonic-like waning discharges may be seen in radiculopathies and mononeuropathies, however myotonia was not restricted to a single muscle here, thus a focal process is unlikely to explain the patient's condition.…”

Section: Discussionmentioning

confidence: 62%

Electrical myotonia and antibiotic induced myasthenic crises: A novel CHRNE variant

Sim¹,

Narasimhalu²

2022

NeuroAsia

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We describe a middle-aged lady who had developed childhood-onset chronic progressive external ophthalmoplegia, fatigable ptosis, and myopathic facies. Unique features of her clinical phenotype included facial weakness that failed to respond to treatment, exacerbation with antibiotic use and electrical myotonia. She responded well to 3,4-diaminopyridine. We highlight aspects of her presentation that led to clinical diagnosis – and, ultimately, genetic confirmation – of a congenital myasthenic syndrome. This underscores the importance of taking a family history and considering inherited causes in cases of seronegative myasthenia.

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“…These data also suggest that patients with MuSK + MG may have myopathic-appearing MUPs earlier in their disease course and in lower MGFA classes compared with AChR + MG who are otherwise similar in age at symptom onset and sex. Although previous case reports support these EDX findings, [10][11][12][13] this study uniquely combines this information in a large series that is matched in a case-control format including MGFA clinical severity score.…”

Section: Discussionmentioning

confidence: 96%

“…The ability to distinguish MuSK + MG from other disorders with EDX testing is supported by recent literature. [10][11][12][13] Electrical myotonic discharges are an unusual EDX feature in neuromuscular junction disorders but have been reported in case studies of patients with MuSK + MG. 10,11 Another study suggested that myopathic motor unit potentials (MUPs) were detected more frequently in MuSK + MG compared with AChR + MG in EDX testing. 12 This finding was confirmed by a separate study that also found myopathic MUPs in a greater number of proximal muscles in patients with MuSK + MG compared with patients with AChR + MG. 13 Collectively, these data indicate that MuSK + MG may have a suggestive EDX profile that, if further defined, may help facilitate a timely diagnosis.…”

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confidence: 99%

Electrodiagnostic Characteristics Suggestive of Muscle-Specific Kinase Myasthenia Gravis

et al. 2022

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Introduction/aims: Muscle specific kinase (MuSK) antibody positive myasthenia gravis (MuSK+MG) is a form of MG with bulbar-predominant symptoms often resistant to conventional treatments. MuSK+MG patients may have an electrodiagnostic (EDX) profile distinct from other MG. This study compares EDX features of MuSK+MG to acetylcholine receptor (AChR) antibody positive MG (AChR+MG) to discern whether any unique EDX patterns exists that can aid in clinical diagnosis.Methods:From January 1 2010 through December 31 2020, all MuSK+MG patients at our institution were identified and randomly matched to an AChR+MG cohort in a 1:2 ratio based on sex, age of onset, and subsequently MGFA clinical severity for a case-control study. Each patient’s clinical profile, treatment, and EDX testing were summarized and analyzed.Results:Twenty-two MuSK+MG patients (18 female) and 44 AChR+MG patients were studied. The average symptom duration at presentation was shorter in the MuSK+MG group (4.7 years) compared to AChR +MG (10.9 years). Myotonic discharges were rare in both groups but more frequently observed in MuSK+MG patients (10%) identified in 5 muscles in 2 patients compared to AChR+MG (2%) noted in only 1 muscle in 1 patient. MuSK+MG patients more often had myopathic appearing motor unit potentials (MUPs) (41% versus 30%) compared to AChR+MG. Myopathic appearing MUPs were found in milder cases of MuSK+MG (MGFA class I-IIB) compared to AChR+MG (MGFA class IIB-V).Conclusions:MuSK+MG patients may have a recognizable EDX profile from AchR+MG that includes: 1) myotonic discharges, 2) greater occurrence of myopathic appearing MUPs in clinically mild disease, and 3) symptoms leading to earlier testing.

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Myotonic Discharges in Anti-MuSK Myasthenia

Cited by 4 publications

References 8 publications

Guidelines on clinical presentation and management of nondystrophic myotonias

Guidelines on clinical presentation and management of nondystrophic myotonias

Electrical myotonia and antibiotic induced myasthenic crises: A novel CHRNE variant

Electrodiagnostic Characteristics Suggestive of Muscle-Specific Kinase Myasthenia Gravis

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