Myopathic (not neuropathic) electrophysiological abnormalities in dynamin 2-related centronuclear myopathy
Department of Physical Medicine and Rehabilitation, University of Medicine and Dentistry of New Jersey, New Jersey Medical School Newark, NJ, USA
Correspondence to: Dr Patrick Foye, DOC suite 3100, 90 Bergen Street, Newark, NJ, USA E-mail: Patrick.Foye{at}UMDNJ.edu
Received April 28, 2006. Accepted June 15, 2006.
Sir, I read with great interest the recent article ‘Characterization of the muscle involvement in dynamin 2-related centronuclear myopathy’ (DNM2-CNM) (Fischer et al., 2006
). I commend the authors for their work in helping us understand how DNM2-CNM is manifested on physical examination, muscle computerized tomography, and so forth.
The article states that out of the nine DNM2-CNM patients who underwent electrodiagnostic testing all patients had myopathic changes on needle electrode examination (NEE) but that four patients had ‘additional neuropathic signs such as pathological spontaneous activity (fibrillations) on NEE and/or a 15–30% reduction of the compound motor action potentials (CMAPs) in some lower leg nerves on nerve conduction studies (NCSs). These results are consistent with features of the axonal Charcot–Marie–Tooth forms.’
As an electromyographer, I would clarify that neither abnormal spontaneous activity (fibrillations) on NEE nor decreased CMAP amplitudes are necessarily ‘neuropathic signs’. Both of these abnormalities can be seen in both neuropathic (axonal) and myopathic conditions. In myopathies, the presumed mechanism for these abnormalities is segmental necrosis along the skeletal muscle syncytium, leaving some segments of the muscle fibres functionally denervated by losing continuity with the neuromuscular junction (Dumitru, 1995). Conversely, with the axonal form of Charcot–Marie–Tooth and other axonal neuropathies, the pathology is at the nerve axon rather than the muscle, but still those same electrophysiological abnormalities are seen. Electrophysiologically differentiating a motor axonopathy from a myopathy relies on analysis of the size, morphology and recruitment of motor units seen on NEE, which I would presume were the ‘myopathic changes’ reported on NEE of all nine DNM2-CNM patients. Thus, it appears that the overall electrophysiological findings in all nine DNM2-CNM patients were most likely purely myopathic, without any true neuropathic features.
I praise the authors for their important article and I hope that my comments may further contribute to the understanding of DNM2-CNM and the centronuclear myopathies in general.
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Dumitru D. (1995) Myopathies. In Dumitru D (Ed.). Electrodiagnostic medicine 1st edn (Hanley & Belfus, Philadelphia) pp. 1031–129.
Fischer D, Herasse M, Bitoun M, Barragan-Campos HM, Chiras J, Laforet P, et al. (2006) Characterization of the muscle involvement in dynamin 2-related centronuclear myopathy. Brain 129:1463–9.
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