title: Peripheral nerve axon involvement in myotonic dystrophy type 1, measured using the automated nerve excitability test.
abstract: OBJECTIVE
  Primary involvement of the peripheral nerves in myotonic dystrophy type I (MyD1) is controversial. We investigated whether the involvement of peripheral nerves is a primary event of MyD1 or secondary to another complication such as diabetes mellitus (DM).
  
  
  METHODS
  The subjects comprised 12 patients with MyD1, 12 with DM and no peripheral nerve involvement, and 25 healthy volunteers. We measured multiple excitability indices in the median motor axons. The strength-duration time constant was calculated from the duration-charge curve, the threshold electrotonus and current-threshold relationships were calculated from the sequential subthreshold current, and the recovery cycle was derived from double suprathreshold stimulation.
  
  
  RESULTS
  The depolarizing and hyperpolarizing threshold electrotonus were significantly reduced and exhibited increased refractoriness in the MyD1 group compared with the DM and control groups. The SDTC, superexcitability, and subexcitability were not significantly altered in the MyD1 group.
  
  
  CONCLUSIONS
  The MyD1 group exhibited a depolarized axonal membrane potential. The significant differences in peripheral nerve excitability between the MyD1 group and the DM and normal control groups suggest that peripheral neuropathy is a primary event in MyD1 rather than a secondary complication of DM.
authors.affiliation: Department of Neurology, Inje University College of Medicine, Busan, Korea. neurobae@yahoo.co.kr
authors.forename: Jong Seok
authors.initials: JS
authors.lastname: Bae
authors.forename: Sang Gin
authors.initials: SG
authors.lastname: Kim
authors.forename: Jeong Cheol
authors.initials: JC
authors.lastname: Lim
authors.forename: Eun Joo
authors.initials: EJ
authors.lastname: Chung
authors.forename: Oeung Kyu
authors.initials: OK
authors.lastname: Kim