The Impact Of Ataxia On Speech And Swallowing Functions

Introduction

Ataxia is the umbrella term for a group of neurological disorders characterised by uncoordinated movements, poor muscle control and speech difficulties. Symptoms and the severity of them differ between individuals and the type of ataxia they have.¹ As a neurological disorder, the function of the nervous system, including the brain, spinal cord and nerves, may be affected. The symptoms experienced indicate which area of the nervous system is affected. Statistics suggest that around 10,000 adults in the UK suffer from ataxia.² Ataxia can impact speech and swallowing functions.

There are 3 main types of ataxia, each named after the area of the nervous system impacted: cerebellar ataxia, sensory ataxia and vestibular ataxia. 

• Cerebellar ataxia - occurs when there is a problem in the cerebellum, the region of the brain responsible for balance, coordination, and voluntary movements³
• Sensory ataxia - caused when the somatosensory system is damaged, the area of the nervous system responsible for providing information on touch and body position. When damaged, sensory signals are disrupted, leading to difficulties with coordination⁴
• Vestibular ataxia - a problem with the inner ears and cochlea, leads to symptoms of nausea, vertigo, and coordination when walking⁴

What is speech and swallowing?

Speech and swallowing are essential functions that massively influence an individual’s quality of life and overall health. Both involve complex neural pathways and coordination of muscles. Swallowing allows for the intake of nutrition and hydration, nourishing the body.⁵ Speech enriches individuals, allowing for the formation and maintenance of social connections. 

Swallowing begins with an oral phase. The cerebral cortex initiates voluntary processes such as chewing, and mixing the food with saliva. After the food and saliva (bolus) reach the pharynx, the involuntary processes begin.⁶ The pharynx contracts, forcing the bolus into the oesophagus. Cranial nerves work throughout this process.

Typically, the desire for speech is initiated in the cerebral cortex by thoughts, causing a cascade of events.⁷ Broca’s area, an area responsible for speech production, relays signals to the motor cortex whereby motor signals are then sent to the relevant cranial nerves for muscle movement. The cerebellum and basal ganglia ensure coordinated movements.

The Pathophysiology of Ataxia

Neurological Basis

The cerebellum, located at the base of the brain, is involved in the coordination of movement and balance/posture. The cerebellum refines movements so that they are smooth and precise.⁸ Dysfunction in the cerebellum impacts motor control, causing a general lack of coordination in voluntary movements. This will be evident by an unsteady gait similar to “drunken” walking, as both lack of limb coordination.⁹

Causes

As previously mentioned, ataxia may be acquired, hereditary, idiopathic and unknown.

• Acquired ataxia - develops due to an external event (any problem that damages the nervous system). This could be a tumour, a stroke, alcoholism, drugs, nutritional deficiency, or infection¹⁰
• Hereditary ataxia - happens due to an internal reason; an abnormal gene is inherited. This gene can be inherited from just one parent (autosomal dominant inheritance), both parents (autosomal recessive inheritance), from the mother to the child (x-linked ataxia), or again from the mother but through the mitochondria (mitochondrial ataxia)¹¹
• Idiopathic ataxia - medical professionals can successfully diagnose the type of ataxia, yet they cannot determine the cause of it
• Unknown ataxia - the cause of the ataxia is unknown

Ataxia's Impact on Speech Functions

Individuals with ataxia may display certain speech characteristics. One of these characteristics is dysarthria, a speech disorder in which the muscles involved are weakened due to neurological damage.¹² Ataxic dysarthria is caused when there is damage to the cerebellum. Symptoms of this type of dysarthria include slurred speech, poor coordination, and difficulty in pronouncing words.¹³ Other symptoms of dysarthria include slow speech rate, hesitation in speaking, irregular rhythm, and difficulty in controlling the volume of speech.¹² Things that can damage the brain and possibly cause dysarthria include stroke, head injury, diseases such as Parkinson’s disease or motor neurone disease, and Down’s syndrome.¹²

Like cerebellar dysfunction, Basal Ganglia dysfunction can cause dysarthria and hypokinetic dysarthria. Due to its dysfunction, the basal ganglia cannot carry out its regular role of initiating smooth movements.¹³ Symptoms of hypokinetic dysarthria include slurred or stuttered speech, monotonal speech and difficulty in pronouncing certain sounds. Basal Ganglia diseases such as Parkinson’s disease are responsible for this type of dysarthria. 

In both cerebellar and basal ganglia dysfunction, muscle coordination is impaired, preventing typical speech. 

Damage to the cranial nerves can lead to difficulty in controlling speech muscles. The trigeminal (V), facial (VII), glossopharyngeal (IX), vagus (X), and hypoglossal nerves control the muscles of the jaw, lips, tongue and throat. When these nerves are damaged, the muscles become weak and fail to function as they should, causing slurred, often incomprehensible speech.¹⁴

How is speech impairment assessed?

Speech impairment is assessed through a combination of clinical evaluations and speech analysis techniques. 

• Medical history - A list of medical questions must be considered such as: What are the symptoms? When was the onset of symptoms? Is there a family history of speech impairment? What medications are they currently, or have they previously taken?¹³
• Language task assessments - typically, these involve the individual repeating words and sentences or carrying out tasks to test their muscles, such as sticking out their tongue or biting their lip¹³
• MRI - is often carried out in order to check for any damage to the neck or brain, or the muscles involved in speech such as the tongue and jaw¹³

How can speech impairments caused by ataxia be treated?

A speech therapist is the most effective method in managing/treating a speech impairment. 

Speech therapists provide support on breath control, articulation, timing, and muscle strengthening exercises.¹³

• Breath control - this can increase speech volume
• Articulation - therapists will encourage clearer pronunciation of words
• Timing - therapists will encourage individuals to slow down their speech for precision and clarity, or speed it up for a better flow
• Muscle strengthening exercises - allow for easier speech

Alternatively, assistive technologies such as computers, writing, and hand gestures are often utilised when speech is severely impaired. 

What may the impact of speech difficulties be on quality of life? 

Speech difficulties are likely to have a social impact. Being unable to communicate can limit an individual's ability to talk to others and make friends, as well as verbally express their emotions. This may put a strain on relationships and can cause social isolation. Additionally, an individual’s professional life may be hindered. Consequently, it is likely that their quality of life is impacted. 

Ataxia's Impact on Swallowing Functions

Ataxic individuals may also experience swallowing difficulties, or dysphagia. Dysphagia is a disorder characterised by trouble swallowing foods, or an inability to swallow foods at all.¹⁵ Dysphagia can be categorised into oesophageal, and oropharyngeal dysphagia. Oesophageal dysphagia refers to food becoming stuck in the throat or chest after swallowing has begun. Oropharyngeal dysphagia is characterised by difficulty in moving food from the mouth into the oesophagus during swallowing, leading to choking or gagging.¹⁶ Other symptoms of dysphagia include a sensation of food being stuck in the throat or chest, and food being brought back up.¹⁵

Mainly two mechanisms in ataxia lead to swallowing difficulties: impaired coordination of swallowing muscles, and a delayed swallow reflex. Like in speech, impaired coordination of muscles has detrimental effects on swallowing. It can lead to inefficient, and sometimes dangerous, transport of food throughout the digestive system.¹⁵ A delayed swallow reflex can lead to choking, or food entering the airways, both of which can become fatal.¹⁷

How is swallowing impairment assessed?

Medical professionals will use a combination of clinical evaluations and instrumental swallowing assessments in order to diagnose a swallowing impairment. Clinical evaluations involve a discussion of the patient’s medical history, medications they take/have taken, an observation of the structures involved in swallowing, and also observations of the patient swallowing different foods to see how their swallowing mechanisms work.¹⁸ Instrumental assessments involve using a type of body imaging. For swallowing assessments, an X-ray is typically used. Whilst undergoing an X-ray, food and drink will be consumed, enabling the identification of any swallowing abnormalities.¹⁸

How can swallowing impairments caused by ataxia be treated?

A combination of swallowing therapy techniques, dietary modifications and feeding tubes may be used to manage/treat swallowing impairments. Swallowing therapy techniques may include exercises to strengthen the muscles involved in swallowing.¹⁹ Additionally, the swallow reflex will be worked on so that it is stimulated in good time. In an attempt to make swallowing easier, softer foods may be swapped for harder foods in an individual's diet. This enables efficient swallowing. Smaller and more frequent meals may be eaten, as well as thicker, yet smaller pieces of food making it easier to swallow.¹⁵ In severe cases, a feeding tube may be required in an attempt to prevent dehydration and malnutrition. Bypassing the oesophagus prevents choking or aspiration of food, protecting the individual from harm.¹⁵ 

What may the Impact of swallowing difficulties be on quality of life? 

Swallowing complications can have detrimental effects on an individual's life. Not only does it pose a threat to life, but it may also take away enjoyable aspects of life, such as enjoying a favourite meal. This can be very frustrating for the individual. In addition, it can impact them socially. A decline in one's mental health at the hands of swallowing difficulties is not uncommon due to the impacts it has on various aspects of life.

What can be done to improve the quality of life of people with dysarthria and dysphagia as a result of ataxia?

Like many illnesses, early diagnosis is profoundly important. In order for this to happen, the symptoms of these disorders must be recognisable by the public as requiring medical attention. Education is imperative to a successful diagnosis and a good prognosis.

Conclusion

Ataxia is a neurological condition that causes impaired coordination of the muscles involved in speech and swallowing. As a result, individuals may experience slurred, stuttered, or slow speech (dysarthria), and/or difficulty swallowing without choking or decreased chewing (dysphagia). Understanding the mechanisms behind dysarthria and dysphagia is important as it enables a timely diagnosis and a successful intervention. A successful diagnosis of each disorder requires a holistic approach, combining clinical evaluations with therapy. Moving forward, continued research is needed in order to better understand the mechanisms of ataxia, and to develop more effective long-term treatments.