Clinical Neurophysiology 126 (2015) 1466–1467
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Dynamic muscle ultrasound – Another extension of the clinical examination See Letter, pages 1638–1639
Many training neurologists and clinical neurophysiologists will have heard the expression, ‘‘electrodiagnostic studies are an extension of the clinical examination.’’ This adage has remained popular due to the ability of electrodiagnostic studies to probe nerve and muscle function akin to the assessment of muscle strength, sensation and deep tendon reﬂexes in the clinical examination, and both remain cornerstones of neuromuscular diagnosis. However, it can be seen from the proliferation of studies evaluating the diagnostic role of ultrasound that neuromuscular medicine is evolving. Multimodality approaches to neuromuscular diagnosis are increasingly reported, with anatomical imaging assessments complementing standard clinical and electrophysiological function assessments. Ultrasound has become well placed to take the lead on this conceptual shift since the introduction of portable, relatively inexpensive ultrasound units capable of producing high quality images at the bedside. One unique feature of ultrasound is the dynamic nature of the examination, which has enabled visualisation of spontaneous muscle movements, the most common being fasciculations. Indeed, a number of studies have evaluated the role of ultrasound detection of fasciculations in amyotrophic lateral sclerosis (ALS; Walker et al., 1990; Reimers et al., 1996; Misawa et al., 2011; Arts et al., 2012; Grimm et al., 2015), with the consensus being that ultrasound is more sensitive than clinical examination or electromyography (EMG) for the detection of fasciculations. Adding ultrasound to EMG assessments increases the diagnostic sensitivity of existing ALS electrodiagnostic criteria (Misawa et al., 2011; Grimm et al., 2015). In this issue of Clinical Neurophysiology, Osaki and colleagues (Osaki et al., 2015) add a novel observation to the catalogue of ultrasound ﬁndings in neuromuscular disease. They describe paired ultrasound and electromyography features in a patient with myokymia associated with familial amyloid neuropathy. On ultrasound, myokymia appeared as ‘‘brief but sustained, tractive movements’’ of the muscle, which contrasts with the brief rotatory muscle movements that are typical of fasciculations and which are readily distinguished from artifactual and voluntary muscle movements by trained observers (Kramer et al., 2014). The term myokymia (Greek; mys – muscle and kymos – wave) denotes involuntary muscle movements, which may be seen as intermittent or continuous fascicular movements on the surface of muscle. Myokymia may be focal, segmental or generalised. Perhaps the most frequent clinical example is eyelid myokymia,
which is commonly reported by normal individuals. In some instances myokymia may be difﬁcult to distinguish from fasciculations on clinical grounds alone. Identifying myokymia, and distinguishing it from fasciculations, may have important diagnostic implications. Myokymia is classically seen following radiation-induced nerve injury (Shin et al., 2013) and has also been reported in a number of other conditions including peripheral nerve hyperexcitability syndromes, nerve trauma, acute and chronic inﬂammatory neuropathies, multiple sclerosis, pontine tumours and episodic ataxia type 1 (Albers et al., 1981; Gutmann, 1991; Simon et al., 2013). Of interest, myokymia may also be seen on EMG studies in ALS, although it is far less frequently seen than fasciculations (Sander et al., 1999; Whaley and Rubin, 2010). Similarly, fasciculations are most frequently seen in peripheral nerve hyperexcitability syndromes (Simon and Kiernan, 2013) but are typically more prominent and widespread in ALS (Mills, 2010; Shimizu et al., 2014). As such, the distribution, frequency and nature of spontaneous muscle movements observed on ultrasound may contribute painless and non-invasive diagnostic information complementary to EMG and clinical examinations. In speciﬁc terms, identifying myokymia in muscles innervated by the same brachial plexus trunk or peripheral nerve may suggest nerve injury, while identifying profuse fasciculations in multiple limb, trunk and craniocervical muscles may be more consistent with a diagnosis of ALS. From an electrophysiological perspective, myokymic discharges consist of rhythmic or semi-rhythmic bursts of individual motor unit potentials that ﬁre in doublet, triplet or multiplet conﬁgurations (Gutmann, 1991). Similarly, fasciculation potentials represent activation of individual motor units, although the morphology of the fasciculation potential often differs from the morphology of the same motor unit potential when voluntarily activated. This is due to the very distal origin of the fasciculation discharge within the axon (Roth, 1982; Layzer, 1994; Kleine et al., 2012) resulting in dyssynchrony of activation of the terminal motor axon arborisation. The main point of difference between the ultrasound appearance of myokymia and fasciculations appears to be the duration of muscle movement, which may reﬂect the electrophysiological differences between each discharge. Each phenomenon represents a motor unit discharge, resulting in torsional movement of a portion of the muscle, with a singular discharge in the case of a fasciculation causing the brief rotatory movement seen on ultrasound, and longer duration multiplet
http://dx.doi.org/10.1016/j.clinph.2014.10.153 1388-2457/Ó 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
Editorial / Clinical Neurophysiology 126 (2015) 1466–1467
discharges in the case of myokymia resulting in more sustained torsional movement. One may suggest that the information obtained by ultrasound in the reported case was duplicative, as the myokymia was apparent on clinical examination and EMG. However, the authors appropriately suggest that ultrasound has easier access to deep muscles than EMG and may be a useful method to non-invasively and quickly screen a broad range of muscles for spontaneous muscle movements. It is unlikely that ultrasound will replace electrodiagnostic studies as an isolated diagnostic study in these situations. Evidence of muscle denervation must also be sought, and if found, active denervation must be separated from purely chronic denervation to reﬁne diagnostic considerations. Although muscle ultrasound may be useful to detect changes of muscle denervation (Pillen et al., 2009; Cartwright et al., 2011; Arts et al., 2012; Simon et al., 2014), further data is needed on the progression of muscle ultrasound characteristics through phases of acute, subacute, and chronic denervation, and subsequent reinnervation (Gunreben and Bogdahn, 1991). In addition, the capacity of ultrasound to detect ﬁbrillations is still debated, despite early reports suggesting this possibility (Pillen et al., 2009; van Alfen et al., 2011). Before dynamic muscle ultrasound can be fully incorporated into the armamentarium of the neuromuscular physician there are a number of important questions that need to be addressed. Can myokymia be reliably distinguished from fasciculations and cramps by blinded observers? Can ultrasound distinguish between electrophysiologically complex and simple fasciculations? Are speciﬁc patterns of fasciculations and other spontaneous muscle movements observed on ultrasound useful to distinguish between different neuromuscular diseases? Answers to these questions and further clinical experience with dynamic muscle ultrasound will concrete this diagnostic modality with electrodiagnostic studies as another natural extension of the clinical examination. Acknowledgements Dr. Simon gratefully acknowledges funding from the National Health and Medical Research Council of Australia and the Motor Neurone Disease Research Institute of Australia (Grant # 1039520). Conﬂict of interest statement: Dr. Simon has no potential conﬂicts of interest to disclose. References Albers JW, Allen AA, Bastron JA, Daube JR. Limb myokymia. Muscle Nerve 1981;4:494–504. Arts IM, Overeem S, Pillen S, Kleine BU, Boekestein WA, Zwarts MJ, et al. Muscle ultrasonography: a diagnostic tool for amyotrophic lateral sclerosis. Clin Neurophysiol 2012;123:1662–7. Cartwright MS, Walker FO, Grifﬁn LP, Caress JB. Peripheral nerve and muscle ultrasound in amyotrophic lateral sclerosis. Muscle Nerve 2011;44:346–51. Grimm A, Prell T, Decard BF, Schumacher U, Witte OW, Axer H, et al. Muscle ultrasonography as an additional diagnostic tool for the diagnosis of amyotrophic lateral sclerosis. Clin Neurophysiol 2015;126:820–7.
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Neil G. Simon Prince of Wales Clinical School, University of New South Wales, Australia Central Clinical School, The University of Sydney, Australia ⇑ Address: Brain and Mind Research Institute, Level 4, 94 Mallett St,
Camperdown, NSW 2050, Australia. Tel.: +61 2 9982 2270; fax: +61 2 9981 7880. E-mail address: [email protected]
Available online 5 November 2014