What is cervical dystonia?

Dystonia is a movement disorder characterised by involuntary muscle contraction. Cervical dystonia affects the head and the neck, so the word cervical in this case means relating to the neck. Cervical dystonia is also sometimes known as spasmodic torticollis (spasmodic, referring to the characteristic muscle spasms and torticollis, relating to the twisting of the neck). It is often a painful condition, causing uncontrollable twisting, repetitive contractions, and abnormal postures that can be very difficult to live with.^1,2 

In this article, we will take a closer look at the mechanisms underlying cervical dystonia. What goes on in the brain that causes some people to develop cervical dystonia? We will look at the part of the brain that controls muscle movement and coordination, and how it is affected in people with cervical dystonia. Living with cervical dystonia can present many challenges both mentally and physically; it is not just a stiff neck. It is important to understand the disorder from the underlying mechanisms to how it presents itself in people, so we can gain a wider understanding of this condition to guide therapies and the way this condition can be managed. 

Cervical dystonia manifests in various ways for each patient It can be beneficial for people with this condition to enhance awareness of the underlying mechanisms in order to be in control and conscious of what is going on with their bodies. 

Symptoms 

Cervical dystonia is a form of focal dystonia where only the head and neck, and sometimes shoulders, are affected. It can manifest differently from one person to another, and the progression of the disease also varies extremely. Some people experience continuous symptoms, while others have intermittent symptoms. Here are some of the most common symptoms of cervical dystonia:³

Abnormal postures of the head which include:

• Rotation of the head
• Tilting of the head (a slight angled movement of the neck forwards, backwards or to the side)
• Bending of the neck (extension of the neck forwards, backwards or to the side)

Other symptoms include:

• Muscle spasms
• Tremors

Non-motor symptoms include:

• Pain
• Headaches
• Poor sleep
• Fatigue
• Depression
• Anxiety

Causes of cervical dystonia

Cervical dystonia is classified as either primary or secondary. Primary cervical dystonia, also referred to as idiopathic cervical dystonia, has no known cause; it may be linked to genetics, although no identifiable gene or mutation has been linked to it. Primary cervical dystonia often begins in adulthood, usually after the age of 30.⁴

Secondary cervical dystonia can often be linked to other underlying conditions that cause damage to the brain and nervous system.⁴

• Trauma, such as stroke or traumatic brain injury,can cause lasting damage to the brain and nervous system
• Infections, such as encephalitis, meningitis, and certain bacterial infections that target the brain and nervous system⁵ 
• Neurodegenerative diseases, such as Parkinson’s disease
• Certain medications, such as dopamine receptor antagonists, block dopamine, which plays a crucial role in the regulation of movement in your brain. Drugs like these are often used to treat mental health conditions such as bipolar disorder and schizophrenia^6,7

Even though cervical dystonia is linked to the causes below, most cases are considered idiopathic and have no obvious cause. There is no clear lesion or abnormality on the brain that can be detected in scans, so it is difficult in the majority of cases to identify a cause or contributing factors. Whether idiopathic or caused by an identifiable injury or disorder, cervical dystonia in both cases presents the same symptoms, as they both have the same underlying mechanisms. This highlights a need for improved diagnostic tools and shows why further research and support are essential for improving our understanding of the deeper brain processes involved.

Underlying mechanisms 

Basal ganglia 

The basal ganglia are a part of the brain that regulates your body’s movement. So, how exactly do we initiate or suppress movement at a neurological level?

The basal ganglia are a set of structures in the brain whose main function is motor control; they help you to carry out smooth, coordinated movements. They work by either allowing the initiation of a movement or inhibiting it; essentially, this is you choosing how you want to move your body. 

The basal ganglia is made up of a few different structures, most importantly:

• Striatum (caudate nucleus and the putamen)
• Globus Pallidus internal (GPi)
• Globus Pallidus external (GPe)
• Subthalamic nucleus
• Substantia Nigra 

All these components help to regulate the activity of the thalamus that sends signals to the motor cortex to initiate movement.⁸

In this set of structures, we have the direct and indirect pathways. The coordination of movement is achieved through the balance of these two pathways. A key structure involved here that can help us to understand the difference in what is occurring here is the Globus pallidus internus, which feeds inhibitory signals to the thalamus. It is like the final step of the pathways in the basal ganglia. The globus pallidus internus is what stops you from making random movements all the time and allows you to stand still; it’s a regulator. Whether we move or not can depend on how much the globus pallidus inhibits the thalamus.

In the direct pathway, the GPi is inhibited, so it works less, meaning it can have less of an inhibitory effect on the thalamus. This enables the thalamus to send more signals to the motor cortex and facilitate movement. The indirect pathway has an opposing effect; it involves the GPe and the Subthalamic nucleus, which send an excitatory signal to the GPi, stimulating it further. If the GPi is more stimulated, it can send more inhibitory signals to the thalamus. So in the indirect pathway, we inhibit the thalamus so it sends fewer excitatory signals to the motor cortex and stops movement.

In people with cervical dystonia, a key pathology we see is a loss of inhibition in the GPi, which allows the thalamus to be overactive and send excessive excitatory signals to the motor cortex, causing abnormal muscle movement and activity, which presents as the symptoms we typically associate with cervical dystonia.⁹

Sensorimotor integration

Sensorimotor integration is how the brain combines sensory signals from the environment with motor control. It is essentially how your environment can influence your movements and how your body reacts to things. 

Sensations and perceptions are not integrated properly into the right parts of the brain, causing the individual to have an impaired sense of head position and movement. Essentially, the brain is misjudging the position of the head and neck and sending wrong motor signals out, which results in the involuntary muscle spasms and incorrect postures we associate with cervical dystonia.¹⁰

Diagnosis

While we understand the underlying mechanisms for dystonia, we lack clear findings in diagnostic testing and imaging. In a sense there is no physical damage to the brain that would show up on a test or scan; dystonia is a condition where the wiring of the brain is intact but misfiring and not working properly. This is why cervical dystonia can be difficult to diagnose and individuals can experience symptoms for years before a clear diagnosis is established. Symptoms may also be subtle at the beginning and onset of the disease.¹¹

In most cases, cervical dystonia is diagnosed through clinical examination, where a practitioner will examine the patient’s head and neck movements and assess for other symptoms such as tremors or pain. Due to clinical examination being the primary form of diagnosis, it is open to bias and can be impacted by a lack of training and education amongst physicians. 

Cervical dystonia can be difficult to diagnose and people can often suffer for many years before receiving a diagnosis. Symptoms can be subtle at the beginning of the disease progression, there can be non-specific symptoms, and a lack of training and education amongst physicians.¹²

Treatment

There is no current cure for cervical dystonia but there are treatments that can help relieve symptoms and improve quality of life for many people living with cervical dystonia. There are two main treatment approaches and they can often be used in conjunction; these are pharmacological intervention and physical therapies. 

The main medication used to treat cervical dystonia is botulinum toxin, also more commonly known as botox, which is cosmetically used to reduce wrinkles. This drug has a relaxing effect on muscles by blocking muscle contraction and can be directly injected into the affected muscles in the neck of people with cervical dystonia.⁹

Oral muscle relaxants and antispasmodic medications can also be taken alongside botulinum toxin injections, such as baclofen and trihexyphenidyl, to give better outcomes and reduce the frequency in which injections are needed.¹³

Physical therapies are often implemented in treatment plans alongside pharmacological intervention and can help to manage the condition further. Physical therapy can help to improve flexibility and increase strength of the neck muscles.¹⁴

Summary 

Cervical dystonia is a complex neurological condition that can greatly affect the lives of those affected by it. This article touched upon some of the underlying mechanisms observed in cervical dystonia and how they contribute to abnormal and involuntary movements of the head and neck. 

Understanding the areas and systems in the brain, which are disrupted in this disorder helps us understand the symptoms people with cervical dystonia experience, and it provides a pathway for further research and guidance on improving treatments, management approaches, and diagnostic testing for diagnosis. 

I hope this article has given you a better understanding of some of the underlying pathologies of cervical dystonia, and while identifying a specific underlying cause is not always clear, the underlying pathologies are still very real, and by learning more about them we can deepen our understanding of cervical dystonia, approach it with greater compassion, and continue to improve treatment options.