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Abstract Details

Determinants of the Repetitive-CMAP Occurrence and Therapy Efficacy in Slow-Channel Myasthenia
Neuromuscular and Clinical Neurophysiology (EMG)
Neuromuscular and Clinical Neurophysiology (EMG) Posters (7:00 AM-5:00 PM)
141
To find determinants of the occurrence of repetitive compound muscle action potential (R-CMAP) and assess the efficacy of channel blocker therapy in slow-channel congenital myasthenic syndrome (SCCMS).

The R-CMAP is an important criterion for diagnosing SCCMS, but is absent in some patients. Most patients respond well to therapy with an AChR channel blocker, but some do not. The reasons for this difference have not been elucidated.

Neurological examination, EMG study, lab test, muscle biopsy, and next generation and Sanger sequencing; review of therapy of previously reported SCCMS patients; simulation of decay phase of end plate potential (EPP).
Three new and 57 reported SCCMS patients with mutations of AChR subunits are included. In patients with R-CMAP, the length of  the mutant  AChR channel opening bursts was increased 8.68 (mean) ± 2.82 (SD) -fold compared to wild-type whereas in patients without R-CMAP it was increased only 3.84 ± 0.65-fold  (95%CI [3.18, 6.50], P = 0.000014). The EPP amplitude after the refractory period of the action potential in muscle fiber is above the threshold in patients with R-CMAP, but below the threshold in patients without R-CMAP. In patients with good results from channel blocker therapy, treatment was initiated 11.60 ± 5.17 years after onset of symptoms; in patients with no to moderate benefit from channel blocker therapy, treatment was initiated 30.70 ± 12.72 years after onset (95%CI[-28.57, -9.63], P = 0.00089). 
The R-CMAP in the SCCMS occurrence is related to the extent of prolongation of the opening episodes of mutant AChR channel. Channel blocker therapy is more effective the sooner it is started after the onset of symptoms. This study provides Class IV evidence that channel blocker therapy in SCCMS patients improves symptoms.
Authors/Disclosures

PRESENTER 		No disclosure on file
No disclosure on file
No disclosure on file
Duygu Selcen, MD, FÂ鶹´«Ã½Ó³»­ (Mayo Clinic) Dr. Selcen has nothing to disclose.
Andrew G. Engel, MD, FÂ鶹´«Ã½Ó³»­ (Mayo Clinic Rochester) The institution of Dr. Engel has received research support from NIH.
Yuwei Da, MD Dr. Da has nothing to disclose.
Xin Ming Shen, PhD, FÂ鶹´«Ã½Ó³»­ (Mayo Clinic) The institution of Dr. Shen has received research support from NIH. The institution of Dr. Shen has received research support from Myasthenia Gravis Foundation of American.