Low frequency repetitive nerve stimulation in anti-muscle specific tyrosine kinase receptor antibody positive myasthenia gravis / 中华神经科杂志

Objective To describe the repetitive nerve stimulation ( RNS) in anti-muscle specific tyrosine kinase (anti-MuSK) receptor antibody positive myasthenia gravis (MG), and compare with anti-acetylcholine receptor ( AChR ) positive myasthenia gravis , to figure out characteristics of anti-MuSK receptor MG.Methods We analyzed clinical and RNS data of nine anti-MuSK receptor MG and 19 age-and sex-matched anti-AChR MG.RNS was performed to the abductor digiti minimi , orbicularis oculi or musculus frontalis and trapezius .Results In anti-MuSK receptor MG , abnormal RNS in facial nerve was seen in 6/9 and in trapezius was 5/9, in limbs was 0.In anti-AChR MG, abnormal RNS in facial nerve was seen in 13/19, in trapezius was 18/19 and in limbs was 7/19.Abnormal in any of three parts was 8/9 and 19/19 in anti-MuSK receptor MG and anti-AChR MG, respectively.The RNS decrementing was more obvious in facial nerve in anti-Musk receptor MG than in anti-AChR MG.Negative prostigmin test was independently associated with anti-MuSK receptor MG (OR=4.25,95% CI 2.19 -15.25, P=0.015). Conclusions Abnormal RNS in any of three parts is more pronounced in anti-AChR MG compared with anti-MuSK receptor MG.RNS decrementing in facial nerve is more obvious in anti-AChR MG.Negative prostigmin test can aid in early suspicion in anti-MuSK receptor MG.

Low frequency repetitive nerve stimulation in anti-muscle specific tyrosine kinase receptor antibody positive myasthenia gravis / 中华神经科杂志

Objective To describe the repetitive nerve stimulation ( RNS) in anti-muscle specific tyrosine kinase (anti-MuSK) receptor antibody positive myasthenia gravis (MG), and compare with anti-acetylcholine receptor ( AChR ) positive myasthenia gravis , to figure out characteristics of anti-MuSK receptor MG.Methods We analyzed clinical and RNS data of nine anti-MuSK receptor MG and 19 age-and sex-matched anti-AChR MG.RNS was performed to the abductor digiti minimi , orbicularis oculi or musculus frontalis and trapezius .Results In anti-MuSK receptor MG , abnormal RNS in facial nerve was seen in 6/9 and in trapezius was 5/9, in limbs was 0.In anti-AChR MG, abnormal RNS in facial nerve was seen in 13/19, in trapezius was 18/19 and in limbs was 7/19.Abnormal in any of three parts was 8/9 and 19/19 in anti-MuSK receptor MG and anti-AChR MG, respectively.The RNS decrementing was more obvious in facial nerve in anti-Musk receptor MG than in anti-AChR MG.Negative prostigmin test was independently associated with anti-MuSK receptor MG (OR=4.25,95% CI 2.19 -15.25, P=0.015). Conclusions Abnormal RNS in any of three parts is more pronounced in anti-AChR MG compared with anti-MuSK receptor MG.RNS decrementing in facial nerve is more obvious in anti-AChR MG.Negative prostigmin test can aid in early suspicion in anti-MuSK receptor MG.

Repetitive Nerve Stimulation in MuSK-Antibody-Positive Myasthenia Gravis

BACKGROUND AND PURPOSE: Responses to repetitive nerve stimulation (RNS) in patients with muscle-specific tyrosine kinase (MuSK) antibody (Ab)-positive myasthenia gravis (MG) vary depending on the muscles tested. We analyzed the RNS responses of limb and facial muscles in MuSK-Ab-positive and acetylcholine receptor (AChR)-Ab-negative MG (MuSK MG) and MuSK-Ab-negative and AChR-Ab-negative [double-seronegative (DSN)] MG patients. METHODS: We retrospectively compared RNS responses between 45 MuSK MG and 29 DSN MG. RNS was applied to the abductor digiti minimi, flexor carpi ulnaris, trapezius, orbicularis oculi, and nasalis muscles. RESULTS: Abnormal RNS responses in limb muscles were observed in 22.2 and 58.6% of MuSK MG and DSN MG patients, respectively, with abnormal facial responses observed in 77.8 and 65.5%, and abnormal responses observed in any of the five muscles in 86.7 and 72.4%. Abnormal RNS responses in the abductor digiti minimi or flexor carpi ulnaris were less frequent in MuSK MG (8.9 and 15.6%, respectively) than in DSN MG (37.9 and 55.2%), whereas the findings for other muscles were not significantly different between the groups. Abnormal facial responses but normal limb responses were independently associated with MuSK MG (odds ratio=5.224, 95% confidence interval=1.300–20.990). CONCLUSIONS: Abnormal RNS responses primarily in facial muscles without involvement of limb muscles were more pronounced in MuSK MG than in DSN MG. RNS of both facial and limb muscles in AChR-Ab-negative MG can increase the test sensitivity and aid in early suspicion of MuSK MG.

Clinical and Electrophysiologic Responses to Acetylcholinesterase Inhibitors in MuSK-Antibody-Positive Myasthenia Gravis: Evidence for Cholinergic Neuromuscular Hyperactivity

BACKGROUND AND PURPOSE: Patients with muscle-specific tyrosine kinase (MuSK) antibody (MuSK-Ab)-positive myasthenia gravis (MG) show distinct responses to acetylcholinesterase inhibitors (AChEIs). Although clinical responses to AChEIs in MuSK-Ab MG are reasonably well known, little is known about the electrophysiologic responses to AChEIs. We therefore investigated the clinical and electrophysiologic responses to AChEIs in MuSK-Ab-positive MG patients. METHODS: We retrospectively reviewed the medical records and electrodiagnostic findings of 17 MG patients (10 MuSK-Ab-positive and 7 MuSK-Ab-negative patients) who underwent electrodiagnostic testing before and after a neostigmine test (NT). RESULTS: The frequency of intolerance to pyridostigmine bromide (PB) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (50% vs. 0%, respectively; p=0.044), while the maximum tolerable dose of PB was lower in the former (90 mg/day vs. 480 mg/day, p=0.023). The frequency of positive NT results was significantly lower in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (40% vs. 100%, p=0.035), while the nicotinic side effects of neostigmine were more frequent in the former (80% vs. 14.3%, p=0.015). Repetitive compound muscle action potentials (R-CMAPs) developed more frequently after NT in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (90% vs. 14.3%, p=0.004). The frequency of a high-frequency-stimulation-induced decrement-increment pattern (DIP) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (100% vs. 17.7%, p=0.003). CONCLUSIONS: These results suggest that MuSK-Ab-positive MG patients exhibit unique and hyperactive responses to AChEIs. Furthermore, R-CMAP and DIP development on a standard AChEI dose may be a distinct neurophysiologic feature indicative of MuSK-Ab-positive MG.

Muscle-Specific Receptor Tyrosine Kinase Antibody Positive Myasthenia Gravis Current Status

Muscle-specific tyrosine-kinase-antibody-positive myasthenia gravis (MuSK-MG) has emerged as a distinct entity since 2001. This disease has been reported worldwide, but with varying rates among patients with generalized acetylcholine-receptor-antibody-negative MG. MuSK-MG was detected in approximately 37% of generalized acetylcholine receptor antibody-negative MG. MuSK-MG patients were predominantly female with more prominent facial and bulbar involvement and more frequent crises. Disease onset tended to be earlier. Patients tended to have a relatively poor edrophonium response but showed prominent decrement in the repetitive nerve stimulation test in the facial muscles. Patients were more likely to display poor tolerance of, or a lack of improvement with, anticholinesterase agents. Somewhat better response was observed with steroids and plasma exchange. Most were managed successfully with aggressive immunomodulatory therapies, although a higher proportion of MuSK-MG patients had a refractory course when compared with other forms of generalized MG. I present here an up-to-date overview on MuSK-MG based on our experience at the University of Alabama at Birmingham and the existing literature.