There are many compelling reasons to use EMG guidance. The first is that EMG ensures that the needle is located in a muscle and in a muscle that is actively contracting in association with the disorder. Speelman and Brans (Cervical dystonia and botulinum treatment: is electromyographic guidance necessary? (Letter). Mov Disor 1995;10(6):802) showed that even the most experienced “blind” injectors were frequently inaccurate in identifying needle placement in muscles of the neck.
The error rate ranged from 15% in an easily palpated superficial cervical muscle, such as sternocleidomastoid, to greater than 50% in deeper muscles, such as levator scapulae and semispinalis capitis (] Dressler D. Botulinum toxin therapy. New York: Theime Stuttgart; 2000).
Comella and colleagues (Botulinum toxin injection for spasmodic torticollis: increased magnitude of benefit with electromyographic assistance. Neurology 1992;42:878–82), in the only published study comparing experienced investigators using EMG versus palpation, showed that EMG was superior in terms of reducing side effects and obtaining clinical benefit.
One simple, often overlooked problem with non–EMG-guided injections is that many injectors use needles too short to reach the muscles they are trying to inject.Axial section through cadaver human neck at C2, showing common needles: 10mm, 15mm, and 37mm EMG needle electrodes, compare healthy versus atrophied depths. Clearly depth oriented guidance cannot be relied upon. (Phys Med Rehabil Clin N Am 14 (2003) 749–766)
Most importantly, EMG provides ongoing information regarding anatomy and activation patterns of muscle to the injector not available from any other technique. Pre-injection evaluation provides the injector with unique information regarding:
- Recognition of patterns of activation
- Location of muscles
- Aspects of anatomy and kinesiology
This is particularly valuable for newer injectors, who rarely have access to large numbers of patients with which to gather experience, familiarity and use of EMG seems to be warranted (Cervical dystonia and botulinum treatment: is electromyographic guidance necessary? (Letter). Mov Disor 1995;10(6):802).
There can be significant issues related to clinicians using specific needle lengths to locate specific muscles. Often times needles are too short to reach the muscles in question. This has to do with, in many cases, due to muscle hypertrophy, in conditions such as cervical dystonia, or in obese patients where extra fat layers place the muscle deeper than expected. EMG guidance has the advantage of identifying that the needle is in muscle
Confirmation of muscle signal is particularly useful in cases where the site may be surrounded by essential nerves and blood vessels
Recent studies showed that both expert and novice needle placements improve with guidance when compared without, even in large easily accessible muscles. (Manual Needle Placement: Accuracy of Botulinum toxin A Injections; October 2012; Muscle and Nerve 46 531-534; Alexis Schnitzler, MD, Nicholas Roche, MD, Philippe DeNormandie, MD, Christine Lautridou, MD, Bernard Parratte, MD, PhD, and Franc Ois Genet, MD)
These studies clearly illustrate that we all do better finding the optimal spots to locate the needles when using EMG guidance, regardless of whether the muscle is located easily on the surface, or deeper, or whether the needle insertions are being carried out by novice or experts.