Absent, unrecognized, and minimal myotonic discharges in myotonic dystrophy type 2.

Nathan P Young, Jasper R Daube, Eric J Sorenson, Margherita Milone

Department of Neurology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905, USA. young.nathan@mayo.edu

Muscle & nerve 2010 Jun

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The purpose of this study was to describe the frequency of absent, unrecognized, or minimal myotonic discharges (MDs) in myotonic dystrophy type 2 (DM2). We performed a retrospective review of needle electromyography (EMG) data prior to genetic diagnosis in 49 DM2 patients at the Mayo Clinic. MDs were not reported on first or repeat EMG studies (n = 8) and not found in archived recordings of 4 patients (8%); archived EMG recordings (n = 4) confirmed the absence of MDs (n = 2), including 1 patient with normal insertional activity in all muscles, and misinterpretation of MDs as slow fibrillation potentials (n = 1) and complex repetitive discharge (CRD) activity (n = 1). Eight (16%) patients had minimal classic MDs with diffusely increased insertional activity, including waning-only MDs in all patients in this group with archived EMG recordings (n = 5). Diffuse MDs were found in 33 (67%) patients. Absent or minimal MDs do not exclude DM2. Over-reliance on diffuse MDs in patients who present with myopathy may lead to delay in genetic diagnosis of DM2.

Citation

Nathan P Young, Jasper R Daube, Eric J Sorenson, Margherita Milone. Absent, unrecognized, and minimal myotonic discharges in myotonic dystrophy type 2. Muscle & nerve. 2010 Jun;41(6):758-62