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 features

• 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