J Clin Neurol.  2011 Jun;7(2):90-95. 10.3988/jcn.2011.7.2.90.

Peripheral Nerve Axon Involvement in Myotonic Dystrophy Type 1, Measured Using the Automated Nerve Excitability Test

• Bae JS
• Kim SG
• Lim JC
• Chung EJ
• Kim OK

• KMID: 2178972
• DOI: http://doi.org/10.3988/jcn.2011.7.2.90

Abstract

BACKGROUND AND PURPOSE
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.

Keyword

myotonic dystrophy; neuropathy; threshold tracking; axonal excitability; nerve excitability test

MeSH Terms

Axons
Diabetes Mellitus
Humans
Membrane Potentials
Myotonic Dystrophy
Peripheral Nerves
Peripheral Nervous System Diseases
Sarcosine
Thiocarbamates
Sarcosine
Thiocarbamates

Figure

• 

  Fig. 1 The mean excitability response in the myotonic dystrophy type I (MyD1), diabetes mellitus (DM), and control groups. The graph shows the threshold electrotonus (A), recovery cycle (B), and current-threshold relationship (C) according to group. The response pattern of the MyD1 group differs from that of the other groups, whereas the pattern is similar in the control and DM groups. The statistical data are given in Table 2.

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