The following is the second article in a series to address applications of Botulinum neurotoxin. The following article is presenting a short review of Cervical Dystonia, with a focus on the benefit of using the Myoguide™ EMG/ESTIM BoNT injection guidance system. The information within, is simply informative and not considered to be instructive, in any way. Please have a look at the details within the appropriate reference materials for more details.
Cervical dystonia (CD), or spasmodic torticollis, is the most common dystonia. CD is a rare condition in which the neck muscles involuntarily contract into abnormal positions. It causes repetitive twisting movements of the head and neck.
The movements can be intermittent, in spasms, or constant. The severity of cervical dystonia varies. It can be painful and disabling in some cases. The specific cause isn’t known. There is no cure, but symptoms can be treated.
There are two forms of cervical dystonia:
- Caput: When the most proximal cervical vertebrae (C1 or C2) are involved
- Collis: When any of the lower cervical vertebrae (C3 to C7) are involved
The “Caput” form (Torticaput) involves muscles that move the skull or head joints; it is further described as Anterocaput, Laterocaput, or Retrocaput.
The “Collis” form involves muscles that control the lower cervical vertebrae and is further described as Anterocollis, Laterocollis, Retrocollis, or Torticollis.
Differentiating the two forms is important because it helps clinicians identify the correct muscles to inject with botulinum toxin.
CD is a common adult-onset cervical dystonia and is usually idiopathic.
Diagnosis is clinical and involves exclusion of tardive dyskinesia, basal ganglia disorders, CNS infections, neck infections and tumors, and drugs.
CD is usually, treated with physical measures, botulinum toxin injection, and/or oral drugs.
Botulinum toxin (BoNT) is a neurotoxin produced by the bacterium Clostridium Botulinum. There are seven types of BoNT (A–G) which bind and cleave one of several neuronal cellular proteins including SNAP-25, Syntaxin or VAMP/Synaptobrevin.
The outcome of BoNT application results in the inhibition of release of acetylcholine (Ach) from the motor neuron terminals resulting in muscle weakness or paralysis. Duration of action depends on cellular regeneration mechanisms, which can take 3-6 months.
Signs and Symptoms of Cervical Dystonia
Cervical dystonia symptoms may begin at any age but usually begin between ages 20 and 60, with a peak between ages 30 and 50.
Symptoms usually begin gradually; rarely, they begin acutely and progress rapidly. Sometimes symptoms begin with a tremor that rotates the neck, in a “no-no” fashion.
The cardinal symptom of cervical dystonia is painful tonic contractions, or intermittent spasms of the Sternocleidomastoid, Trapezius, and other neck muscles, usually unilaterally, that result in an abnormal head position.
Common muscles involved include:
|Sternocleidomastoid M.||Levator Scapulae M.|
|Trapezius M.||Scalenus Medius M.|
|Splenius Capitis M.||Scalenus Anterior M.|
Unilateral Sternocleidomastoid muscle contraction causes the head to rotate to the opposite side. Rotation may involve any plane but almost always has a horizontal component. Besides rotational tilting (torticollis), the head can tilt laterally (laterocollis), forward (anterocollis), or backward (retrocollis, common when dopamine-blocking drugs are the cause). Similarly, in the caput form, the head may tilt laterally (laterocaput), forward (anterocaput), or backward (retrocaput).
Spasmodic torticollis ranges from mild to severe. Usually, it progresses slowly for 1 to 5 years, then plateaus.
About 10 to 20% of patients recover spontaneously within 5 years of onset (usually in milder cases with onset at a younger age). However, it may persist for life and can result in restricted movement and postural deformity.
Treatment of Cervical Dystonia
Treatment of CD usually involves botulinum toxin injections, or oral medication.
Spasms can sometimes be temporarily inhibited by physical therapy and massage, including sensory biofeedback techniques, and by light touch (geste antagoniste).
For the purpose of this discussion we will address treatment involving the injection of botulinum toxin (type A or B) into the dystonic muscles. BoNT injection has been shown to reduce painful spasms for 1 to 4 months in about 70% of patients, restoring a more neutral position of the head.
However, in very few cases, when the toxin is repeatedly injected, BoNT can become less effective, because of the development of neutralizing antibodies against the toxin can foil pharmacological activity.
Oral drugs can usually relieve pain, but they suppress dystonic movements in only about 25 to 33% of patients.
EMG Guidance Helps Find the Target
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.
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.
Myoguide can be used to improve patient outcomes by improving accuracy.
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Beth E Crowner, Cervical Dystonia: Disease Profile and Clinical Management, Physical Therapy, Volume 87, Issue 11, 1 November 2007, Pages 1511–1526, https://doi.org/10.2522/ptj.20060272