Motor Neurone Disease

Devastating condition causing progressive weakness and eventually death, usually as a result of respiratory failure or aspiration

Aetiology

  • Males and females equally affected by MND
  • 90% sporadic, 10% familial
    • Sporadic MND peaks at the ages of 50-75 years and declines after age 80
  • Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease (MND) phenotype in adults
  • ALS is slightly less common in non-Caucasian populations

Pathophysiology

  • Predominantly affects upper and lower motor neurones in the spinal cord, cranial nerve motor nuclei and cortex

Clinical presentation

  • Classically, there is a combination of upper motor neuron and lower motor neuron signs.
  • Upper motor neuron signs include spasticity, hyperreflexia and upgoing plantars (though they are often down going in MND)
  • Lower motor neuron signs include fasciculations, and later atrophy
  • Generally, the eye and sphincter muscles are spared until late in the disease course and sensory disturbance is NOT seen
  • Focal onset and continuous spread, finally generalised paresis

Clinical patterns

The four clinical groups are:
  • Spinal ALS - the classic MND syndrome
    • Simultaneous involvement of upper and lower motor neurones, usually in one limb, spreading gradually to other limbs and trunk muscles
    • Split hand syndrome - preferential wasting of thenar group is a typical pattern of atrophy seen in ALS
  • Bulbar ALS - early tongue and bulbar involvement
    • Dysarthria, dysphagia, nasal regurgitation of fluids and choking are the presenting symptoms
  • Progressive muscular atrophy - only lower motor neurone features
    • Pure lower motor neurone presentation with weakness, muscle wasting and fasciculations, usually starting in one limb and gradually spreading to involve other adjacent spinal segments
  • Primary lateral sclerosis - only upper motor neuron features (1-2% - rare)
    • Confined to upper motor neurones, causing a slowly progressive tetraparesis and pseudobulbar palsy
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Investigations

  • Diagnosis is largely clinical
  • Investigations allow exclusion of other disorders and may confirm subclinical involvement of muscle groups, such as paraspinal muscles
  • Denervation of muscles due to degeneration of lower motor neurones is confirmed by EMG

Management

On-going management

  • Key worker assessing needs and coordination of care
  • Communication needs - speech therapy, AAC
  • Nutritional needs - dieticians, gastrostomy
    • Metabolic rate in MND is doubled - weight loss of >10% at diagnosis is a poor survival indicator
  • Respiratory needs - assessment, home ventilation
  • Riluzole is a sodium-channel blocker that inhibits glutamate release - slows progression slightly, increasing life expectancy by 3–4 months on average

Symptomatic treatments

  • Sialorrhoea - hyoscine/buscopan, glycopyrronium, botox, suction
  • Nutrition - supplements/thickeners, liquid drug preparations
  • Bulbar dysfunction - early communicator, nutritional support, care for upper respiratory tract
  • Limb dysfunction - washing, dressing, feeding, turning in bed, mobility aids/hoists often necessary
  • Muscle cramps - quinine, baclofen
  • Muscle spasms - baclofen, tizanidine, dantroline, gabapentin
  • Emotional lability - sometimes treated with antidepressants
  • Cognitive impairment - always be aware of capacity