Introduction 

Huntington’s Disease (HD), also known as Huntington’s chorea, is a devastating inherited neurodegenerative condition characterised by a movement disorder (chorea), dementia, and behavioural and neuropsychiatric issues. This condition is caused by the HTT gene or chromosome 4 mutation.

It progressively impairs the brain’s ability to coordinate voluntary movements, resulting in a wide range of motor defects. Initially, it presents with subtle coordination challenges and involuntary movements. As the disease progresses, symptoms intensify into profound difficulties with walking, speech, and swallowing.

Fine motor skills essential for daily tasks, such as writing, eating, and dressing, are significantly compromised, severely dampening independence and quality of life. The decline in motor skills can also affect communication, social interactions, and overall well-being. Understanding the impact of motor dysfunction is vital to enhance treatment interventions and support for individuals with HD.¹

Early motor symptoms 

Chorea 

Chorea is a hallmark symptom of early-stage HD. It is caused by basal ganglia degeneration and dopamine overactivity. Chorea is a series of involuntary, irregular, unpredictable, non-stereotyped jerky movements that flow from one muscle to the next.

Initially, it appears subtly among fingers, hands, and facial muscles, often presenting as minor twitches, fidgetiness, or restlessness. This often leads chorea to be misinterpreted as benign habits or nervous tics during the condition's early stages. When the disease progresses, chorea becomes more pronounced affecting gross motor functioning and coordination.¹ 

Motor incoordination

Motor incoordination (ataxia) is caused by cerebellar atrophy and progressive Purkinje cell loss. Initially, it presents as subtle disruptions of smooth voluntary movements, resulting in impaired rapid alternating movements and fine motor tasks, such as reaching, writing, and buttoning clothes. Individuals develop a lack of motor precision and coordination, leading to postural and stance instability. Loss of coordination results in overall clumsiness and increased risk of fall or injury.^2,3

Dystonia 

Dystonia is distinct from chorea, as it is caused by thalamostriatal (thalamus and striatum) and cholinergic neuron degeneration. Dystonia involves involuntary and sustained muscle contractions (spasms) that result in unwanted twisting or repetitive movements. It can present as subtle muscle contractions in the hands, feet, and neck, leading to twitching or abnormal posture. Due to its uncontrollability and variability, dystonic movement can greatly hinder coordination and daily activities, further exacerbating motor impairments.⁴

Subtle motor changes 

Due to the various brain regions affected, hyperkinetic (excessive movement) choreatic phases usually plateau as time passes, followed by a hypokinetic (decreased movement) phase. Other subtle motor changes include:¹

• Dyspraxia
• Tremors
• Reduced manual dexterity
• Eye movement abnormalities (e.g., gaze impersistence/distractability, delayed initiation, and slowed-down saccades) 

Progression of motor impairments 

Worsening chorea 

As HD progresses, chorea often gets worse substantially. What used to be mild and intermittent can intensify and become more persistent and invasive, spreading from fingers and facial muscles towards limbs. These exaggerated choreic movements will also become increasingly difficult to control, making daily activities, such as cooking, driving, walking, speaking, and eating more challenging.

Bradykinesia 

Symptoms of Parkinsonism are common in individuals with middle-late-stage HD. One notable Parkinsonian symptom is bradykinesia, which is characterised by slowed movements. Bradykinesia occurs due to the degeneration of basal ganglia output to the supplementary motor cortex, which is important for sequential movement initiation and maintenance.^5,6

Individuals often exhibit reduced movement initiation and execution speed of both fine and gross motor tasks. Bradykinesia can also reduce automatic or repetitive movements, such as blinking, facial expressions (hypomimia), and arm swinging while walking.⁷

Rigidity 

Rigidity is another common Parkinsonian symptom of HD that becomes more pronounced during the middle stages. It involves:

• Muscle stiffness
• Inflexibility
• Hypertonia (resistance to passive movements)
• Difficulty stretching or relaxing their muscles (resulting in a sense of tightness, pain, and muscle cramps)

Rigidity can also lead to impaired balance and postural changes, causing movements to become effortful and uncomfortable. Rigidity worsens voluntary movement coordination difficulties, making ordinary tasks like swinging arms, turning over in bed, facial expressions, chewing, swallowing, and breathing more challenging.⁸

Impaired gait and balance 

Gait and balance impairment is another common symptom that affects one’s mobility and daily functioning during the middle stage of HD. Gait disturbances may present in an irregular, unsteady pattern, with steps becoming more wide-based, hesitated, and uncoordinated. Balance issues may increase your risk of falls and injuries, and postural instability will affect upright posture maintenance.^2,7,9 

Severe motor dysfunction 

Individuals often experience a significant loss of voluntary movement control, leading to motor challenges during advanced HD. The combined effect of chorea, ataxia, and Parkinsonism-related motor dysfunctions may escalate into akinesia and mutism when symptoms are advanced.

One’s mobility becomes severely impaired in having minimal ability to initiate or control voluntary movements, making simple tasks like shifting positions, speaking, and swallowing extremely challenging, or even impossible. Severe motor impairment can also cause a significant decline in independence and quality of life, resulting in reliance on assistive devices and caregivers for mobility and basic activities.⁷ 

Dysarthria (speech difficulties) 

Dysarthria is a common symptom of late-stage HD, affecting communication and social interaction. These speech impairments can present as hyperkinetic dysarthria, characterised by fast, unpredictable, and difficult-to-understand speech due to excessive, irrelevant, and involuntary muscle movement. The voice volume and pitch may also change when speaking. As the condition progresses, individuals may struggle to:

• Find appropriate words
• Form coherent sentences
• Control the speed and rhythm of speech

These symptoms not only affect verbal communication but also make it harder for effective needs, thoughts, and emotional expression. This can result in feelings of powerlessness, frustration, and isolation.

Dysphagia (swallowing difficulties) 

Dysphagia may become more pronounced and can pose serious risks to the health and well-being of people with HD. Swallowing difficulties can manifest as:

• Difficulty chewing
• Difficulty moving liquid from the mouth to the throat
• Incomplete swallow initiation
• Delayed swallowing reflex

The inability to enjoy mealtimes and social events can lead to social isolation and depression. Muscle weakness and coordination issues can severely impair the ability to swallow safely as the disease progresses, resulting in:

• Weight loss
• Malnutrition
• Dehydration
• Potential risk of choking and aspiration pneumonia

Hence, multidisciplinary dysphagia management for individuals with late-stage HD is vital to ensure proper and safe nutritional obtainment.

Impact on daily living and quality of life 

Dependence on caregivers 

As a degenerative disease, individuals with HD often become increasingly dependent on caregivers for support with basic daily activities and personal care. The complex motor, cognitive, and behavioural symptoms could further impede one’s independence, making ordinary tasks like eating, dressing, and moving challenging or even impossible.

Caregivers are essential in providing physical assistance and emotional support, whilst coordinating medical care. While their involvement is crucial in ensuring the safety and well-being of individuals with HD, safeguarding caregivers’ well-being by avoiding burnout, and emotional and financial strain among families, is also of equal importance.

Psychosocial impact 

HD could exert substantial psychosocial effects on individuals and their families. The progressive motor, cognitive, and communicative decline, could lead to frustration, helplessness, and social withdrawal. Coping with the uncertainty of the disease course and its impact on daily life can result in anxiety and depression.

Maintaining relationships and engaging in social activities may become increasingly difficult, worsening isolation and loneliness. Overall, providing access to support services and a strong support network are crucial to improving the well-being of both those with HD and their caregivers.¹⁰

Management strategies 

Managing motor impairments in HD involves a multidisciplinary approach to improve quality of life. Physical therapy focuses on maintaining mobility and function through exercise and movement strategies. Occupational therapy addresses daily activities, in adapting environments to enhance independence. Speech therapy targets interventions towards effective communication and swallowing abilities. Medications can help manage and reduce chorea, such as:

• Tetrabenazine
• Deutetrabenazine
• Haloperidol 

Counselling, psychotherapeutic services, and medications (e.g., antidepressants, antipsychotics, and mood stabilisers) can also help to address emotional symptoms like depression and anxiety.

Summary 

Huntington’s disease (HD) is a degenerative condition that can profoundly impact motor skills from subtle changes to severe impairments. Initially, it manifests as minor involuntary movements (chorea), which can evolve into vigorous choretic motions, rigidity, bradykinesia, impaired gait, and balance issues. In severe cases, there is a significant loss of voluntary movement control, which greatly affects daily functioning, independence, and communication.

To support individual needs, a multidisciplinary approach should be taken. Treatment may include physical, occupational, and speech therapy, medications, assistive devices, and psychological support. Treatment plans should be tailored to individual needs as the disease progresses, to maintain quality of life amidst the evolving motor dysfunctions.