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Motor Neurone Disease

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Overview

Motor neurone disease (MND) is a progressive neurodegenerative disorder of unknown aetiology characterised by the degeneration of upper motor neurones (UMNs), lower motor neurones (LMNs) or both. It can lead to paralysis and death. Most cases of MND are due to amyotrophic lateral sclerosis (ALS), however, there can be other types.

Types

Some MNDs and their types are:

  • UMNs and LMNs:
    • Amyotrophic lateral sclerosis (ALS)
  • UMNs only:
    • Primary lateral sclerosis
    • Pseudobulbar palsy
  • LMNs only:
    • Progressive muscular atrophy
    • Progressive bulbar palsy

General Features

Patients can present with a wide range of signs and symptoms. MND rarely presents before 40 years. Some features that suggest MND are:

  • Generally no sensory signs or symptoms
  • Fasciculations
  • UMNs and LMNs
  • Muscle wasting
  • No ocular muscle involvement
  • No cerebellar signs
  • Weight loss

Some patients may have other features, such as:

  • The consequences of muscle weakness e.g. clumsiness/falls
  • Speech/swallowing problems/tongue fasciculations – known as bulbar presentation
  • Shortness of breath on exertion/dyspnoea that cannot be explained by respiratory causes
  • Behavioural changes – emotional lability
  • Frontotemporal dementia
  • More specific features are discussed under each subtype

Amyotrophic Lateral Sclerosis

Overview

‘A’ – no, ‘myo’ – muscle, ‘trophic’ nourishment, ‘lateral’ – anterior and lateral columns of the spinal cord, and ‘sclerosis’ – scarring. Amyotrophic lateral sclerosis (ALS) describes the scarring of the anterior and lateral columns of the spinal cord leading to a loss of motor neurone innervation to muscles. This leads to muscle wasting and atrophy.

Features

General features of MND are mentioned above. Features suggesting ALS include:

  • A mixture of UMN and LMN signs – this is a distinctive feature of ALS
  • Asymmetric limb weakness – the most common presentation
  • Some patients may have bulbar-onset ALS (~25%):
    • UMN and LMN cranial nerve signs – dysphagia and speech difficulties
    • This is followed by limb involvement in later stages

Primary Lateral Sclerosis

Overview

‘Primary’ – damage to UMNs not part of another disorder, ‘lateral’ – lateral columns of the spinal cord, and ‘sclerosis’ – scarring. Primary lateral sclerosis (PLS) only affects UMNs and there is no muscle wasting (amyotrophy) initially.

Features

  • PLS has UMN signs only
  • The progression of PLS is much slower than ALS
  • Over time, patients may develop LMN symptoms

Pseudobulbar Palsy

Overview

‘Bulbar’ – the medulla and regions of the brainstem that control the muscles of the face, ‘palsy’ – weakness or paralysis. The ‘pseudo’ part describes the fact that the bulbar palsy is not due to direct damage to the muscles and LMNs, but is instead due to damage to the corticobulbar pathways (UMNs). 

Features

Progressive Muscular Atrophy

Overview

Progressive muscular atrophy (PMA) describes the progressive degeneration of LMNs leading to muscle atrophy.

Features

PMA has LMN features only:

  • Fasciculations
  • Muscle weakness
  • Muscle atrophy
  • Reduced/absent reflexes

Progressive Bulbar Palsy

Overview

‘Bulbar’ – the medulla and regions of the brainstem that control the muscles of the face, ‘palsy’ – weakness or paralysis.

Features

  • Dysphagia
  • Dysarthria
  • Mouth weakness
  • Tongue weakness

Differential Diagnoses

Degenerative cervical myelopathy

  • LMN signs are present at the level of the lesion
  • UMN signs are below the lesion
  • Usually has associated sensory symptoms and bladder/bowel dysfunction

Myasthenia gravis (MG)

  • MG is not a central nervous system (CNS) disorder and affects neuromuscular junctions, so UMN and LMNs are not present
  • Symptoms fluctuate and usually worsen towards the end of the day
  • Ocular symptoms are present e.g. diplopia

Charcot-Marie-Tooth (CMT) disease

  • CMT disease is not a CNS disorder but a peripheral nervous system disorder. UMNs are not present, but LMNs may be (peripheral nerves include LMNs, whereas UMNs are in the CNS). 
  • There are sensory signs involved
  • Causes distal muscle weakness and atrophy
  • Onset is usually earlier on in life and CMT is not life-threatening

Investigations and Diagnosis

  • Diagnosis is clinical
  • Consider EMG:
    • Motor conduction is normal, slowing suggests an alternate diagnosis

Management

Overview

MND is non-curable and usually leads to death within a few years with disability preceding it. Management is using a multidisciplinary approach. For ALS, riluzole can be given and prolongs survival by about 2-3 months. Management also involves:

  • Non-invasive ventilation
  • Mucolytics
  • Palliative care
  • Respiratory support – non-invasive ventilation (usually BIPAP) is used at night
  • Nutrition support – percutaneous gastrostomy tube (PEG) is ideal

Monitoring and Patient Advice

Monitoring

  • Patients have their FVC monitored to assess for respiratory decline every 3 months
  • Patients should have opportunities to discuss end-of-life care. This may involve discussions relating to:
    • Hospice care
    • Lasting powers of attorney
    • Advance directives

Patient Advice

  • Patients should seek help if any new signs or symptoms arise so they can be managed. These can include muscle cramps, stiffness, tone, saliva, choking, depression, pain etc. 

Complications and Prognosis

Complications

  • Respiratory failure and death
  • Pneumonia secondary to infection/aspiration
  • Depression
  • UTIs
  • Constipation
  • Loss of speech
  • Complications of immobility e.g. ulcers

Prognosis

  • MND is usually rapidly progressive and median survival is 2-4 years
  • More than 90% of patients die in their sleep
  • Factors associated with a poorer prognosis are:
    • Bulbar presentation
    • Weight loss
    • Poor respiratory function
    • Older age

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