Value of short exercise and short exercise with cooling tests in diagnosis of recessive form of myotonia congenita (Becker disease) - are sex differences important?

In myotonia congenita (MC), activation with exercise or cooling can induce transient changes in compound motor action potential (CMAP) parameters, thus providing a guide to genetic analysis. We performed the short exercise test (SET) and the short exercise test with cooling (SETC) in 30 patients with genetically confirmed Becker disease (BMC) to estimate their utility in the diagnosis of BMC. Although we observed a significant decrease in CMAP amplitude immediately after maximal voluntary effort in both tests in the whole BMC group, in men this decline was significantly smaller than in women, especially in SET. Clinical implications/future directions: In men with a clinical suspicion of BMC, a small decrease in CMAP amplitude in SET together with a typical decline in SETC does not exclude the diagnosis of BMC. Our results show a sex-specific difference in chloride channel function in BMC, which needs further investigation.