Motor neurone disease

• Motor neurone disease is a term that encompasses a variety of specific diseases affecting the motor nerves - both upper and lower

  It is a progressive, eventually fatal condition - most common type of MND is amyotrophic lateral sclerosis (ALS)
• The typical patient is a late middle-aged (e.g., 60) man, possibly with an affected relative. There is an insidious, progressive weakness of the muscles throughout the body, affecting the limbs, trunk, face and speech. The weakness is often first noticed in the upper limbs. There may be increased fatigue when exercising. They may complain of clumsiness, dropping things more often or tripping over. They can develop slurred speech (dysarthria).
• Signs of lower motor neurone disease:

  • Muscle wasting
  • Reduced tone
  • Fasciculations (twitches in the muscles)
  • Reduced reflexes
• Signs of upper motor neurone disease:

  • Increased tone or spasticity
  • Brisk reflexes
  • Upgoing plantar reflex
• Patients with motor neurone disease tend to die of respiratory failure or pneumonia.

   
• Riluzole can slow the progression of the disease and extend survival by several months in ALS
• The most common presentation of MND is unilateral limb weakness - wrist or foot drop may be noted
• Another common presentation is dysarthria and dysphagia
• Investigations for MND are mostly to rule out other causes:

  • Nerve conduction studies/EMG - sensory function is normal
  • Genetic testing
  • MRI - MND can cause increased T2 weighted signalling
  • routine bloods including B12
  • Autoantibodies - to exclude myasthenia gravis
• Progressive bulbar palsy is the second most common form of MND - tongue wasting and fasciculations
• There is a strong association between ALS and frontotemporal dementia which affects around 15% of patients. All patients should be screened at presentation and at regular follow-ups for dementia.
• There is a median survival of 3-5 years after symptom onset
• The most common forms of presentation are asymmetrical limb onset (around 80%) followed by bulbar onset (around 20%).