Peripheral nerve involvement in myotonic dystrophy type 2 – similar or different than in myotonic dystrophy type 1?

Introduction Multisystem manifestations of myotonic dystrophies type 1 (DM1) and 2 (DM2) are well known. Peripheral nerve involvement has been reported in DM1 but not in genetically confirmed DM2. The aim of our study was to assess peripheral nerve involvement in DM2 using nerve conduction studies and to compare these results with findings in DM1. Methods We prospectively studied patients with genetically confirmed DM2 (n=30) and DM1 (n=32). All patients underwent detailed neurological examination and nerve conduction studies. Results Abnormalities in electrophysiological studies were found in 26.67% of patients with DM2 and in 28.13% of patients with DM1 but the criteria of polyneuropathy were fulfilled in only 13.33% of patients with DM2 and 12.5% of patients with DM1. The polyneuropathy was subclinical, and no correlation was found between its presence and patient age or disease duration. Conclusions Peripheral nerves are quite frequently involved in DM2, but abnormalities meeting the criteria of polyneuropathy are rarely found. The incidence of peripheral nerve involvement is similar in both types of myotonic dystrophy

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

Introduction: 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.Material and methods: 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.Results: 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