[Electrophysiological features of patients with myotonic dystrophy type 1]

To explore the electromyography (EMG) and nerve conduction (NC) features of patients with myotonic dystrophy type 1 (DM1).

Routine PCR and triplet primed-PCR (TP-PCR) were performed for 33 clinically diagnosed DM1 cases at our clinic from June 2009 to June 2012. The EMG and NC results of 30 patients with a genetic diagnosis of DM1 were collected and analyzed.

Myotonic discharges were found in all patients and EMG revealed myogenic changes in 29 patients. Among all 123 muscles examined, the incidence of myotonic discharges was, a little higher than that of myogenic changes (91.87% vs 90.24%). The rate of myotonic discharges in distal muscles was higher than that of myotonic discharges in proximal muscles (100% vs 83.61%). And the difference was statistically significant. No difference existed in myogenic changes between distal and proximal muscles.(87.10% vs 93.44%) Nerve conduction was all normal.

Myotonic discharges and myogenic changes are important EMG features in DM1. In early stage of DM1, myotonic discharges may be the isolated EMG abnormality. Myotonic discharges are predominantly detected in distal muscles. The involved regions detected by EMG are wider than those of clinical findings. EMG is an important screening tool for subclinical or early atypical DM1 patients.