Medicine – Motor Neurone Disease (Amyotrophic Lateral Sclerosis)

Motor neurone disease (MND) is a progressive neurodegenerative disorder affecting motor neurones. The term amyotrophic lateral sclerosis (ALS) is often used for the common form in which both upper motor neurones and lower motor neurones are involved.

Although the original note emphasizes anterior horn cells, ALS affects more than just the spinal anterior horn. It also involves corticospinal pathways and motor nuclei in the brainstem, which explains the mixture of UMN, LMN, bulbar, and respiratory features.

1. Main Pathology

The disease causes progressive degeneration of:

Upper motor neurones in the motor cortex and corticospinal tracts.

Lower motor neurones in the anterior horn cells of the spinal cord.

Motor cranial nerve nuclei in the brainstem.

This creates the characteristic combination of:

UMN signs + LMN signs in the same patient.

2. Upper Motor Neurone Signs

Upper motor neurone involvement may cause:

Increased tone or spasticity.

Brisk reflexes.

Clonus.

Extensor plantar responses.

Spastic dysarthria when corticobulbar pathways are involved.

These signs reflect degeneration of descending motor pathways.

3. Lower Motor Neurone Signs

Lower motor neurone involvement produces:

Muscle weakness.

Muscle wasting.

Fasciculations.

Reduced tone in affected muscles.

Reduced reflexes where LMN involvement is severe.

The combination of wasting and fasciculation with brisk reflexes elsewhere is particularly suggestive of MND.

4. Limb Weakness

Weakness is progressive and may begin focally.

The upper limbs are commonly affected, and weakness may be particularly noticeable in the hands.

Patients may report difficulty with:

Buttons.

Writing.

Turning keys.

Opening jars.

Using cutlery.

Progression may then involve other limbs.

5. Hand Wasting

Wasting of the intrinsic hand muscles can be an early and striking feature.

The patient may develop:

Interosseous muscle wasting.

Thenar or hypothenar wasting.

Weak grip.

Loss of fine finger movements.

This reflects lower motor neurone degeneration.

6. Fasciculations

Fasciculations are visible spontaneous contractions of individual motor units.

They may appear as brief twitching under the skin.

Fasciculations are common in MND but are not specific on their own, because benign fasciculations can also occur.

Their significance is much greater when accompanied by:

Progressive weakness + muscle wasting + other UMN or LMN signs.

7. Foot Drop

Weakness of ankle dorsiflexion can produce foot drop.

The patient may develop:

High-stepping gait.

Toe catching.

Frequent tripping.

Foot drop may be an early manifestation when lower motor neurone weakness begins in the distal leg.

8. Bulbar Symptoms

Bulbar involvement occurs when motor neurones controlling speech and swallowing are affected.

Patients may develop:

Dysarthria.

Dysphagia.

Weak cough.

Choking episodes.

Aspiration.

Both bulbar palsy and pseudobulbar palsy features may occur because both LMN and UMN pathways can be involved.

9. Bulbar Palsy Features

Bulbar palsy reflects lower motor neurone involvement of the cranial nerve nuclei or their peripheral fibres.

Typical findings include:

Weak, nasal, or slurred speech.

Dysphagia.

Nasal regurgitation.

Tongue wasting.

Tongue fasciculations.

Reduced bulbar reflexes in some patients.

10. Pseudobulbar Features

Pseudobulbar palsy reflects bilateral upper motor neurone corticobulbar involvement.

Typical findings include:

Spastic or strained dysarthria.

Brisk jaw jerk.

Spastic tongue without prominent fasciculations.

Emotional lability or pseudobulbar affect.

In MND, bulbar and pseudobulbar findings may coexist.

11. Dysphagia and Aspiration

Swallowing impairment is a major clinical problem.

Patients may experience:

Coughing during meals.

Choking.

Weight loss.

Recurrent chest infections.

Aspiration pneumonia.

Progressive dysphagia may require enteral feeding support.

12. Respiratory Muscle Weakness

Respiratory failure is a major cause of morbidity and mortality in MND.

Weakness may involve:

Diaphragm.

Intercostal muscles.

Accessory respiratory muscles.

Patients may develop:

Dyspnoea.

Orthopnoea.

Morning headaches from nocturnal hypoventilation.

Poor sleep.

Daytime somnolence.

Weak cough.

13. No Sensory Signs

A classic feature of MND is the relative preservation of sensation.

Patients generally do not develop prominent:

Numbness.

Loss of vibration sense.

Loss of pain or temperature sensation.

Therefore:

Progressive motor weakness with UMN + LMN signs and no sensory loss strongly suggests MND.

Minor sensory symptoms can occur in real-world practice, but significant objective sensory loss should prompt consideration of alternative diagnoses.

14. Other Functions Often Relatively Preserved

Classically, the following are relatively preserved until late:

Sensation.

Eye movements.

Sphincter function.

However, not every patient fits a perfect textbook pattern.

Some patients can develop cognitive or behavioural changes, particularly in association with frontotemporal dementia.

15. Cognitive and Behavioural Involvement

MND is not always purely motor.

A subset of patients develop:

Executive dysfunction.

Behavioural change.

Language difficulties.

Frontotemporal dementia.

This is especially important because ALS and frontotemporal degeneration can overlap clinically and genetically.

16. Diagnosis

MND is primarily a clinical diagnosis based on progressive motor dysfunction with evidence of both UMN and LMN involvement.

The clinician looks for:

Progression over time.

Spread from one body region to another.

UMN signs.

LMN signs.

Absence of a better alternative diagnosis.

17. Electromyography

EMG is a key supportive investigation.

It can demonstrate widespread active and chronic denervation.

Typical findings may include:

Fibrillation potentials.

Positive sharp waves.

Fasciculation potentials.

Large-amplitude, long-duration motor-unit potentials from reinnervation.

EMG helps confirm LMN involvement even in muscles that may not yet appear weak clinically.

18. Nerve Conduction Studies

Nerve conduction studies are usually performed alongside EMG.

They help distinguish MND from peripheral neuropathies and other disorders.

In classic ALS:

Sensory nerve conduction is usually relatively preserved.

Motor studies may show abnormalities related to axonal loss.

Therefore, the original statement that NCS directly “reveals anterior horn cell damage” is a simplification; EMG is more directly useful for demonstrating denervation, while NCS helps exclude alternative peripheral nerve disease.

19. Other Investigations

Other investigations are mainly used to exclude mimics.

These may include:

MRI of brain and spinal cord.

Blood tests.

Thyroid function.

Vitamin B12.

Autoimmune or infectious testing where appropriate.

The exact investigation depends on the clinical presentation.

20. Important Mimics

Conditions that may resemble MND include:

Cervical myelopathy.

Peripheral neuropathy.

Multifocal motor neuropathy.

Myasthenia gravis.

Myopathies.

Vitamin B12 deficiency.

Structural spinal cord disease.

The absence of sensory loss helps, but imaging and neurophysiology are often required to exclude treatable mimics.

21. Riluzole

Riluzole is a disease-modifying treatment used in ALS.

It reduces glutamatergic neurotransmission and provides a modest survival benefit.

It does not reverse established motor neurone loss but may slow progression modestly.

22. Edaravone

In some healthcare systems and selected patients, edaravone may also be used.

It is thought to reduce oxidative cellular injury.

Eligibility and benefit vary by patient and jurisdiction, so its role is more selective than basic supportive care.

23. Muscle Relaxants

Spasticity may be treated with agents such as:

Baclofen.

Tizanidine.

Other treatments may be considered depending on severity.

The aim is to reduce painful stiffness while avoiding excessive weakness or sedation.

24. Management of Dysphagia

Progressive swallowing difficulty requires careful nutritional assessment.

Management may include:

Diet modification.

Speech and language therapy.

High-calorie nutritional support.

Enteral feeding when oral intake becomes unsafe or inadequate.

25. PEG Feeding

A percutaneous endoscopic gastrostomy, PEG, can provide nutritional support when swallowing is severely impaired.

It may help reduce:

Weight loss.

Dehydration.

Difficulty taking medication.

It does not completely eliminate aspiration risk because saliva and refluxed material can still be aspirated.

Timing is important because the procedure becomes more risky as respiratory function deteriorates.

26. Respiratory Support

The original note lists CPAP, but the more important respiratory support in MND is usually non-invasive ventilation, especially bilevel positive airway pressure.

This is because the major problem is alveolar hypoventilation from respiratory muscle weakness, rather than upper-airway collapse alone.

Therefore:

MND respiratory failure → NIV/BiPAP-type support is typically more relevant than ordinary CPAP.

27. Non-Invasive Ventilation

Non-invasive ventilation can improve:

Nocturnal hypoventilation.

Sleep quality.

Daytime symptoms.

Quality of life.

Survival in appropriately selected patients.

It is one of the most important supportive interventions in progressive respiratory muscle weakness.

28. Tracheostomy Ventilation

Some patients may choose tracheostomy with invasive ventilation.

This can provide long-term respiratory support but involves major implications for:

Communication.

Mobility.

Care requirements.

Quality of life.

Advance-care planning.

These decisions require detailed multidisciplinary discussion.

29. Secretion and Cough Management

Weak cough can lead to retained respiratory secretions.

Management may include:

Physiotherapy.

Mechanical cough-assist devices.

Suction when required.

Treatment of excessive saliva.

These measures reduce respiratory complications.

30. Communication Support

Progressive bulbar and limb weakness may impair speech and writing.

Communication aids may include:

Voice amplification.

Tablet or computer-based communication systems.

Eye-gaze technology.

Speech-generating devices.

Early planning is useful before speech deteriorates severely.

31. Multidisciplinary Team Approach

Management is best coordinated through a multidisciplinary team.

This may include:

Neurology.

Respiratory medicine.

Physiotherapy.

Occupational therapy.

Speech and language therapy.

Dietetic support.

Palliative care.

Psychological and social support.

This approach helps address the wide range of motor, nutritional, respiratory, communication, and psychosocial needs.

32. Prognosis

MND is progressive, but survival varies greatly between patients.

Older teaching sometimes gives:

Approximately 2 years for bulbar-onset disease.

Approximately 4 years for limb-onset disease.

These figures are too rigid to apply to individual patients.

In general, bulbar-onset disease tends to have a poorer prognosis than limb-onset disease, but survival ranges widely from months to many years.

33. Factors Associated with Prognosis

Prognosis depends on several factors, including:

Site of onset.

Age at onset.

Rate of progression.

Respiratory involvement.

Nutritional status.

Cognitive or behavioural involvement.

Response to supportive interventions.

Therefore, individual prognosis cannot be predicted accurately from onset pattern alone.

34. Motor Neurone Disease – Note Form

Disease: progressive neurodegenerative motor-system disorder.

ALS: common MND phenotype involving both UMN and LMN degeneration.

Structures involved: motor cortex/corticospinal tracts + anterior horn cells + motor brainstem nuclei.

UMN signs: spasticity, hyperreflexia, clonus and extensor plantars.

LMN signs: weakness, wasting, fasciculations and reduced reflexes in affected muscles.

Limb pattern: progressive weakness, often involving hands or distal limbs.

Foot drop: may occur from distal leg weakness.

Bulbar LMN signs: nasal/weak speech, tongue wasting/fasciculations, dysphagia.

Pseudobulbar UMN signs: spastic dysarthria, brisk jaw jerk and emotional lability.

Respiratory involvement: progressive respiratory muscle weakness and hypoventilation.

Sensation: usually preserved.

Diagnosis: primarily clinical.

EMG: demonstrates widespread denervation and reinnervation.

Nerve conduction studies: help exclude peripheral neuropathy; sensory conduction is usually relatively preserved.

Riluzole: modest disease-modifying survival benefit.

Spasticity treatment: baclofen, tizanidine or similar agents when appropriate.

Feeding support: PEG may be considered for progressive dysphagia and weight loss.

Respiratory support: non-invasive ventilation, usually bilevel support, is more appropriate than simple CPAP for hypoventilation.

Communication: computer, speech-generating and eye-gaze devices.

Care: multidisciplinary and increasingly palliative/supportive as disease progresses.

35. Characteristic Examination Pattern

A very characteristic examination finding is:

Muscle wasting + fasciculations + brisk reflexes + extensor plantars.

This shows simultaneous:

LMN degeneration → wasting and fasciculations.

and

UMN degeneration → hyperreflexia and extensor plantar responses.

When this occurs with progressive weakness and no significant sensory loss, MND becomes a major diagnostic consideration.

Key Clinical Pattern

Think of ALS/MND as:

Progressive MOTOR disease with BOTH UMN and LMN signs, but little or no sensory loss.

The classic pattern is:

Weakness + wasting + fasciculations + hyperreflexia/spasticity + extensor plantars.

Bulbar disease causes:

Dysarthria + dysphagia + aspiration risk.

Respiratory involvement causes:

Progressive hypoventilation and respiratory failure.

For treatment, remember:

Riluzole + symptom control + nutrition/PEG + non-invasive ventilation + communication support + multidisciplinary care.

And one important correction:

Respiratory muscle weakness in MND is usually managed with non-invasive bilevel ventilation rather than standard CPAP.