Management of Focal Hand Dystonia

The following is the third article in a series to address applications of Botulinum neurotoxin. The following article is presenting a short review of Hand 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.

For more details about BoNT injection guidance please contact us directly.

Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both.

Dystonia is also based on extent of body parts involved.  Focal hand dystonia (FHD) is a common form of adult onset focal dystonia (Karp, 2010).  Focal dystonia does not have a cure, but treatment can reduce spasms and perhaps keep them from worsening. 

FHD is usually task specific where the hand has been repeatedly used for a particular activity for a long period of time (Torres-Russotto et al, 2008). Task specific dystonia is characterized by patients having difficulty in executing a specific activity with otherwise no other difficulties in using hand. They can virtually arise from any task, can remain task specific, or can lose specificity over time.

Common muscles involved include:

In difficult situations, both EMG and STIM-guided injection are useful in identifying muscles and guiding the injection (see below).

In a study only 37% of needle placement attempt reached the target muscles or muscle fascicles without EMG guidance, demonstrating the importance of EMG guidance (Semerdjieva, 2016)

Common types of FHD include writer’s cramp, musician’s dystonia (e.g. string instruments and piano), and golfer’s yips (involuntary wrist spasms that occur most commonly when golfers are trying to putt).

Typically, this form of dystonia is task specific, but in some patients this specificity may be lost over a period of time. Segmental or generalized dystonia may also start off as an FHD.

Treatment includes oral medications, injection botulinum neurotoxin (BoNT), neurosurgery (including neurostimulation), and rehabilitation.

Treatment approaches can include:

Lifestyle changes:  Changing the approach to tasks to create new brain processes to evoke movements; e.g. a violinist may opt to wear a glove to reduce triggers while performing; writers may change their grip on their writing instruments.

Medications: Anticholinergics can help block nerve signals that cause muscle spasms. Vesicular monoamine transporter 2 inhibitors can be used to change brain chemicals that affect nerves and muscles; Levodopa/Carbidopa may alleviate symptoms; Muscle relaxants may also be used.

Injections: Botulinum neurotoxin (BoNT) injections are commonly used in dystonia treatment protocols.  These injections interfere with brain signals that cause spasms. The duration of this treatment is typically 3-4 months.

Surgery: Rarely used, but may include deep brain stimulation, which involves implanting a device to generate stimulation signals to effect activity.   Other surgical approaches may be used to release nerves that cause muscle spasms (selective denervation)

Rehabilitation: This may include a combination of constraint-induced therapy and specific motor control retraining may be a successful strategy for the treatment of musicians’ FHD.

Results suggest that retraining strategies may need to be carried out for at least 8 months before statistically significant changes are noted

BoNT injection has been extensively studied in writer’s cramp patients and found to be effective. 

Selection of muscles and injection technique are crucial in getting best results.

Botulinum Toxin in FHD

Botulinum toxin is the main modality of treatment in patients of FHD. Different types of botulinum toxins are available, however, most of the therapeutic trials on FHD have been with BoNT-A. 

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 weakening of the target muscles, or paralysis.  Duration of action depends on cellular regeneration mechanisms, which can take 3-6 months.

Botulinum toxin has also been thought to have central effects, as well. Studies in animal models show that BoNT undergoes retrograde and transynaptic transport to affect the spinal cord and brain (Lawrence et al, 2012) (Matak et al, 2012)

Many studies have been conducted to assess the efficacy of botulinum toxin in FHD, with the majority of studies being focused on writer’s cramp and musician’s dystonia.

To summarize the reviewed studies, BoNT is an effective and safe therapeutic modality in patients with FHD and has not been associated with serious side effects.

Long-term studies have also found no adverse effects of its use and the possibility of antibody formation against botulinum toxin in the longer run is remote.

The drawbacks however include its short duration of beneficial action and the cost.

Research supports BoNT being effective in the treatment of FHD and recommended to be considered in such patients (Simpson et al, 2008).

BoNT might still not have clear cut evidence to be unequivocally effective in this group of patients, however with the lack of other effective treatment modalities it remains the mainstay of therapy in patients with FHD.

The Value of Electrical Stimulation Guidance in the Management of FHD

Electrical stimulation (ESTIM) guidance increases the accuracy of hypodermic needle electrode placement, compared to simply using anatomical knowledge (AKO) placement by using muscle activation.

The potential advantage of ESTIM is that not only does it ensure that the injecting needle is in the target muscle, but that the needle is in close proximity to motor endplates and/or motor points (Childers, 2010). Electrical stimulation is easy to perform, does not require formal training, and does not prolong the procedure significantly.

However, it does require experience/practice in electrophysiological techniques as well as familiarity with the relevant anatomical landmarks, which we assume is the standard of practice.

While it has been proven that EMG guidance does perform consistently better than AKO approaches, even in large muscles (Speelman et al, 1995) (Comella et al, 1992) (Schnitzler et al,, 2012), ESTIM is useful, in particular applications, and certainly within the hand, for validation before injection of BoNT.

In the case where there are multiple smaller muscles present in the vicinity, especially when dealing with the hand, ESTIM provides a simple way to double check that EMG is actually coming from the expected muscle.  Please have a look at some of our clinical videos on this subject.

Myoguide is equipped with what is essentially a single channel EMG machine with a full featured, built in stimulator.

Myoguide’s stimulator presents 5 stimulation frequency choices, four pulse width choices, and 1- 20 mA of stimulation current available in both 1.0 mA and 0.1 mA steps.

0.1 mA steps are helpful and necessary for nerve location procedures allow evoking responses at lower, more comfortable stimulation levels.  

Pulse widths of up to 500 microseconds allow evoking muscle twitches at lower currents, yielding a more comfortable clinical experience for patients undergoing stimulation location procedures.

Wider stimulation choices allow evoking twitch at lower, more comfortable stimulation levels. 

Myoguide has an exclusive feature, “Stimulation Pause” which allows clinicians to easily halt the stimulation process.  This is especially useful when repositioning the injection needle electrode in order to fine tune its location for a more accurate injection point.  Stimulation can easily be returned to the pre-paused current level with the touch of any button.

The goal is to validate that the needle tip location is within the correct muscle, by being able to witness the twitch in the correct location.  The needle is easily partially withdrawn and repositioned for another try, if corrections are needed.

Myoguide™ EMG/ESTIM BoNT injection guidance system is designed to amplify EMG signals from muscle and provide audio and visual feedback to assist clinicians in locating areas of muscle activity.

Myoguide also has an integrated and well featured stimulator, capable of stimulation in either 1.0 mA or 0.1 mA steps, for muscle, nerve, and motor endplate location procedures.

Myoguide supports injection of neuromodulators and both chemodenervation and neurolytic procedures, as well as, peripheral nerve stimulation. Learn more about how to use Myoguide

The Myoguide™ Store has everything you need, 24/7 for your Myoguide™ patient encounters, including Myoguide™, original and new cable options, and Technomed electrodes! Buy direct for easy ordering and get your BONUS 2-year warranty!

References

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