Low frequency repetitive nerve stimulation in anti-muscle specific tyrosine kinase receptor antibody positive myasthenia gravis

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. Key words: Myasthenia gravis; Receptors, cholinergic; Prostigmin; Muscle-specific tyrosine kinase receptor