Anti-MuSK-positive myasthenia gravis: neuromuscular transmission failure in facial and limb muscles.
The presence of antibodies against muscle-specific receptor tyrosine kinase (MuSK) appears to define a subgroup of patients with myasthenia gravis (MG) characterized by weakness predominant in bulbar, facial and neck muscles compared with anti-acetylcholine receptor (AChR) antibody-positive MG. To investigate the patterns and severity of neuromuscular transmission failure in different muscles in MuSK-positive MG, we performed single fiber electromyography (SFEMG) in the facial (frontalis) and limb (extensor digitorum communis, EDC) muscles in three anti-Musk-positive patients, and compared results with those of 11 anti-AChR-positive patients. Only one of the three MuSK-positive patients had abnormal jitter in EDC, but all the three showed clearly increased jitter in the frontalis. By contrast, the AChR-positive patients showed similarly abnormal jitter for the two muscles. These results suggest that when the diagnosis of anti-MuSK-positive MG is suspected, SFEMG should be performed in most prominently affected muscles.
Kuwabara
S
S
Department of Neurology, Chiba University School of Medicine, Chiba, Japan. kuwabara-s@faculty.chiba-u.jp
Nemoto
Y
Y
Misawa
S
S
Takahashi
H
H
Kawaguchi
N
N
Hattori
T
T
D000906:Antibodies / Q000097:blood*; D004576:Electromyography; D005145:Face; D005260:Female; D006801:Humans; D007866:Leg; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009157:Myasthenia Gravis / Q000097:blood* / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000503:physiopathology; D020794:Receptor Protein-Tyrosine Kinases / Q000276:immunology*; D011950:Receptors, Cholinergic / Q000276:immunology*
D000906:Antibodies; D011950:Receptors, Cholinergic; C095714:MUSK protein, human; D020794:Receptor Protein-Tyrosine Kinases