P48-T Short exercise and short exercise with cooling tests in recessive myotonia congenita (Becker disease)

Abstract

Background In myotonia congenita provocative tests may induce transient or persistent changes in compound motor action potential (CMAP) parameters. These changes are variable and correspond to partial inexcitability of the myotonic muscle membrane. Specific patterns of response in electrophysiological exercise tests correlate with the underlying genotype, thus providing a guide to genetic analysis. The aim of this study was to estimate the utility of the short exercise test (SET) and short exercise test with cooling (SETC) in diagnosis of Becker disease (BMC). Material and Methods SET and SETC were performed in 30 patients with genetically confirmed BMC (19 men; 63.33%) with the mean age 29.4 ± 15.4 years; (range: 4–61). The mean age of disease onset was 8.1 ± 4.2 years (range: 0.5–19) and the mean disease duration 21.3 ± 16.8 years (range: 0–56.5). Results In the whole group we observed a significant decrease in CMAP amplitude immediately after effort in both tests. We noticed statistically significant sex differences in response to effort and cold. In men marked decline in CMAP amplitude was seen only in SETC whereas in SET no such changes were observed. In women evident CMAP decrement was seen in both tests. Conclusions In male patients with clinical suspicion of myotonia congenita atypical response in SET together with typical result in SETC does not exclude the diagnosis of BMC. Function of chloride channel in BMC might be modulated by sex specific factors, what needs further investigation in a larger group of patients.