What's The Difference Between Parkinson's Disease and Motor Neurone Disease?

Parkinson’s disease (PD) is a well-known neurological disorder that leads to dementia, affecting our movement, balance, emotions, etc.¹ However, many people confuse it with another condition, called motor neurone disease (MND), due to their shared symptoms, such as loss of muscle control.^2,3 

Motor neurone disease is a collection of many neurological disorders, however, Parkinson’s disease is not included as one of them. There are many differences between PD and MND:

• Causes: Whilst PD is caused by dopamine deficiency in basal ganglia within the central nervous system (CNS),³ MND is caused by the death of motor neurones both within the CNS and the peripheral nervous system (PNS), leading to the muscles²
• Symptoms and Diagnosis: Both MND and PD show symptoms such as muscle weakness, swallowing difficulties and emotional changes. However, whilst early onset PD can be diagnosed using MRI with high accuracy, MND cannot be detected using a single test. A combination of blood tests, MRI, lumbar puncture, etc., needs to be used to diagnose MND only in later stages^4,5  
• Onset risks and conditions: The progression of MND is faster and less stable than PD. MND is fatal, as it will cause difficulties in breathing and eating at later stages of the condition. PD, however, does not cause patients to die. The most severe PD patients can become disabled when untreated, due to the lack of motor control^1,4   

Although both Parkinson’s disease and MND are neurodegenerative diseases that lead to dementia, patients need to distinguish them and receive specific treatments. 

What is parkinson’s disease

Parkinson’s disease is one of the most common types of dementia, caused by accumulated cell damage and dopamine deficiency in the brain.⁶ It mainly occurs amongst people over aged 50, with a higher incidence amongst men than women.¹ 

Signs and symptoms

Symptoms of PD develop slowly over years, and they are mostly associated with loss of motor control. 

The signs of Parkinson’s disease include: 

• Slow and inflexible movement
• Tremors 
• Loss of coordination and balance
• Emotional changes and memory loss
• Muscle stiffness

PD patients may also experience other age-related symptoms, including speaking difficulties and confusion.¹ Detailed symptoms can be found on the NHS website. 

To distinguish PD from other neurological disorders, resting-state fMRI can be used to detect the level of neuronal connectivity in basal ganglia.⁷ A significant fall in functional connectivity and increased abnormal activities (firing of signals) in the basal ganglia are markers of parkinsonism.^8,9 

Causes and risk factors

Cell death occurs naturally as we age. However, when the process starts to impair the function of dopaminergic neurones in the basal ganglia, the pathology of PD would occur. The exact genetic and environmental factors are yet to be confirmed.^10,11 

Normally, neurones in the basal ganglia would release a neurotransmitter called dopamine, which monitors our movement by sending instructions to other parts of the brain, through direct and indirect pathways.¹² Of which, the direct pathway has an excitatory effect on our motor control. This involves the connection between the thalamus, the cortex, and the motor components in the basal ganglia, including the substantia nigra and the subthalamic nuclei. The basal ganglia-thalamo-cortical loop is activated by dopamine, which would enable the correct instructions to be sent to the upper motor neurones in the brainstem.^13,14,15  

Dopamine deficiency in the basal ganglia would excessively activate indirect pathways, which disrupts the original loop and reduces motor control.^16,17,18 The lack of connectivity in the brain regions involved in motor control would lead to symptoms of PD, such as trembling and loss of coordination. 

Complications

The most common complications of Parkinson’s disease are:^19,20

• Falling due to muscle weakness and reduced motor control
• Problem swallowing
• Sleeping difficulty
• Depression/anxiety
• Vulnerability towards infections (pneumonia)

Although Parkinson’s disease is not fatal, it increases the risk of death due to other complications.²⁰ Other than Parkinson’s disease, parkinsonism can occasionally occur because of antipsychotic drug intake, progressive supranuclear palsy, and cerebrovascular disease such as strokes.¹ Other types of dementia associated with the deposit of the lewy body can also be confused with PD, such as Alzheimer’s disease and Lewy body dementia.²⁵ These are complications during PD diagnosis due to their shared symptoms. 

Diagnosis

Clinicians diagnose Parkinson’s disease based on the patient’s symptoms, family and medical history, and other examinations such as brain scans. For instance, fMRIcan be used to assess brain connectivity and detect abnormalities in various brain regions;⁷ HPLC can also be used to detect the neurotransmitter levels in the brain to monitor patients’ conditions.²¹ 

When to see a doctor

Visit a doctor when you discover symptoms, such as shaking, slow movement and muscle rigidity. For specialists to confirm the disease, you will be asked to describe your symptoms and perform movements, followed by physical examinations. You will be prescribed medications such as levodopa and the change in neurotransmitter level would be monitored by HPLC.^1,21 An improvement of the condition upon levodopa intake would allow clinicians to confirm PD. 

What is motor neurone disease

Motor neurone disease (MND) is a collection of diseases that cause damage to the motor neurones. These include amyotrophic lateral sclerosis (ALS), progressive bulbar palsy (PBP), progressive muscular atrophy, primary lateral sclerosis, spinal muscular atrophy, etc. MND mainly occurs amongst people over 60. The progression of MND varies from one to another, and the severe condition may cause mortality. However, treatment options are available to relieve the symptoms.^2,4 

Signs and symptoms

The most common signs of MND are:⁴

• Muscle weakness and loss of balance
• Speaking and swallowing difficulties
• Emotional changes 
• Twitching
• Weight loss

The symptoms are worsened over time, and muscles in the respiratory system may become dysfunctional in severe cases. This may lead to mortality. 

Causes and risk factors

Suspected genetic and environmental risk factors are being studied by the national institute and other organisations. Up to 10% of MND patients have a family history of MND. Other environmental risk factors, such as intense exercise, agricultural chemicals and heavy metals, injuries, and electrical trauma, may also give rise to MND. However, like Parkinson’s disease, the exact risk factors of MND are yet to be confirmed.²² 

As a neurodegenerative disease, MND is caused by abnormal cell deaths in motor neurones. Of which, upper motor neurones lie within the CNS, and lower motor neurones lie in the brainstem (in the CNS) and spinal cord (in the PNS), leading to skeletal muscles.^4,23 Unlike Parkinson’s disease, which is caused by dysfunctions only within the brain (Basal ganglia), MND is caused by damages in the motor neurones that connect the brain with the rest of the body. 

The reasons for abnormal cell deaths can be:²²

• Distorted cell structure due to cytoskeleton damage.
• RNA mutations lead to dysfunctional proteins. 
• Protein aggregation in the wrong region of the motor neurones.
• Excessive chemical messenger, glutamate, between motor neurones, leads to toxicity.
• Cells produce excessive waste, and antioxidants do not function 
• Dysfunctional mitochondria
• Damaged glial cells surrounding motor neurones, failing to protect the neurones
• Lack of nutrients

Complications

The early stages of MND can hardly be detected, as the symptoms overlap with many other neurological diseases that lead to dementia. A portion of patients with ALS also develop frontotemporal dementia, which would affect patients’ personalities and speaking skills.²⁴ The major cause of death is breathing difficulties and loss of lung functions.  

Diagnosis

A single test cannot confirm the disease. Physical and neurological assessments need to be done to test the motor skill, nerve functions, cognitions, personality changes, etc. ² 

A combination of Electromyography (EMG) and nerve conduction study is used to distinguish lower motor neurone disease from muscle dysfunctions. MRI, blood and urine test, and nerve biopsy are also used for the confirmation of NMD.² 

When to see a doctor

Visit a doctor when you observe symptoms of MND, especially when you have a family history of MND or frontotemporal dementia. Genetic testing and physical examinations can be used to confirm some subtypes of MND, including familial ALS.^2,4

What's the difference between parkinson's disease and motor neurone disease?

Despite both being neurodegenerative diseases, the fundamental causes of PD and MND are different. Whilst PD is caused by dopamine deficiency in basal ganglia, MND is caused by cell damage in the motor neurones. The symptoms of PD involve involuntary tremors, which makes it more distinguishable than MND; the tests for PD are also more advanced and accurate. Most importantly, despite leading to potential disabilities, PD is not fatal; MND can progress faster and would lead to breathing and swallowing difficulties, eventually leading to death.  

What are the similarities? 

Both PD and MND are neurological diseases that lead to dementia, which means they are both associated with ageing and abnormal cell deaths. The exact causes of both diseases are unknown, but changes in the brain and the motor neurones can be tested using physical and neurological examinations, such as EMG and MRI. Both PD and MND are associated with patients’ motor control.

Can they be treated in the same way? 

No, as PD and MND are caused by different factors. Medications such as levodopa are used for PD, to  repair the dopamine level in the substantia nigra in the brain. Deep brain stimulation (DBS) can be used to treat PD symptoms alongside medications to reduce tremors, muscle stiffness, etc.²⁶ However, this approach cannot be used to treat MND, as MND is caused by lack of “signals” between motor neurones, rather than “signal misfiring” like PD. DBS cannot fix the missing neurones. 

Treatment for MND includes physiotherapy, occupational therapy, language therapists, etc., and helping with your day-to-day tasks. A medicine named riluzole would help to block the glutamate release, and slow down the progression of MND.^4,27  

Which is more common? 

Parkinson’s disease is more common than MND. Parkinson’s disease is the second most common neurodegenerative disease that leads to dementia, with the first being Alzheimer’s disease. The prevalence of MND is 3.37 out of 100,000, whereas 1 in 500 people can get PD.^1,28 

Summary

Despite many similarities and associations, there are major differences between Parkinson’s disease and motor neurone disease, from the mechanisms to the diagnostic approaches and treatment options. If your family member is showing symptoms of either disease, it is advisable to visit a doctor and receive appropriate examinations and treatment. Understanding the difference between PD and MND would allow you to set up different life expectations, enabling the right support to be provided for you.