P.100Pseudo-increment at repetitive nerve stimulation (Arzel's sign): a new tool for Brody myopathy diagnosis

Abstract

Brody myopathy (BM) is a recessive condition caused by mutations in the ATP2A1 gene and usually induced impaired muscle relaxation on exercise. Diagnosis relies on electroneuromyography (ENMG), showing electrical silence during muscle stiffness, decreased SERCA activity on muscle biopsy and genetic analysis of ATP2A1 gene. ENMG functional analyses are very useful in the diagnosis of channelopathies. Therefore, we hypothesized that they might be impaired in BM. We performed exercise tests and repetitive nerve stimulations (RNS) in 11 patients with BM. They all showed incremental response at 3 Hz RNS. Indeed there was an increase value of the compound motor action potential (CMAP), especially in the ulnar nerve (+30.2 ± 7.1 %, p<0.001), and decreased CMAP duration (-30.3 ± 2.8 %, p < 0.001). Interestingly, this sign, referred to as the Arzel's sign, was useful in the diagnostic procedure of patients with Brody disease, even for those with atypical phenotype. The Arzel's sign is easily accessible, and could prove to be a very useful tool in diagnosis BM and broadening its phenotype.