Neurophysiological and mitochondrial abnormalities in MuSK antibody seropositive myasthenia gravis compared to other immunological subtypes

Mariapaola Marino, Emanuela Bartoccioni, Flavia Scuderi, A. Rostedt Punga, K. Ahlqvist, A. Suomalainen, H. Kalimo, E. V. Stålberg

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Objective: To compare the electrophysiological and histopathological features of immunological myasthenia gravis (MG) subtypes. Methods: Fifty MG patients underwent clinical examination, MuSK-Ab and AChR-Ab analysis. The majority underwent quantitative and single-fiber electromyography (QEMG, SFEMG), repetitive nerve stimulation and deltoid muscle biopsy. From muscle specimens with histological mitochondrial dysfunction, we amplified mitochondrial DNA (mtDNA). In specimens with mtDNA deletions, the nuclear gene POLG1 was sequenced. Results: Five AChR-Ab seropositive [AChR(+)] and 5 seronegative [AChR(-)] patients were MuSK-Ab seropositive [MuSK(+)]. Five of 7 neurophysiologically examined MuSK(+) patients (71%) had proximal myopathic pattern, compared to 7 of 31 MuSK(-)/AChR(+) patients (23%) (P=0.012). SFEMG was abnormal in all examined MuSK(+) patients. All 7 biopsied MuSK(+) and 32 MuSK(-) patients (89%) had cytochrome c oxidase (COX) negative fibers. Three of five MuSK(+) and 13 of 20 MuSK(-) patients analyzed had multiple mtDNA deletions but no POLG1 mutations. Conclusions: Similar degree of SFEMG abnormalities was present in proximal muscles among MuSK(+) and AChR(+) patients. Proximal myopathy was over-represented in MuSK(+) patients; however, both MuSK(+) and MuSK(-) patients had mild myopathy with frequent mitochondrial abnormalities. Significance: The weakness in MuSK(+) patients is most likely due to disturbed neuromuscular transmission. The frequently encountered mitochondrial dysfunction in MG warrants further study. © 2006 International Federation of Clinical Neurophysiology.
Original languageEnglish
Pages (from-to)1434-1443
Number of pages10
JournalClinical Neurophysiology
Publication statusPublished - 2006


  • Action Potentials
  • Adult
  • Aged
  • Antibodies
  • Case-Control Studies
  • DNA, Mitochondrial
  • Electric Stimulation
  • Electromyography
  • Electron Transport Complex IV
  • Female
  • Humans
  • Immunoglobulins
  • Male
  • Middle Aged
  • Mitochondria, Muscle
  • MuSK
  • Muscle Fibers, Skeletal
  • Muscle, Skeletal
  • Myasthenia Gravis
  • Myasthenia gravis
  • Myopathy
  • Prospective Studies
  • Quantitative EMG
  • Receptor Protein-Tyrosine Kinases
  • Receptors, Cholinergic
  • Reverse Transcriptase Polymerase Chain Reaction
  • Single-fiber EMG
  • mtDNA deletions


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