Motor neuron disease

Background

  • Neurodegenerative condition characterised by loss of upper and lower motor neurons throughout the nervous system.
  • Incidence ~2/100,000 and prevalence ~7/100,000; average age of onset ~65, although around 10% can present <45 years; males>females
  • Most cases are sporadic but 5-10% are familial
    • Genes associated include SOD1 gene (20% of familial cases)
  • Several different forms of MND, most common of which is amyotrophic lateral sclerosis (ALS) (other types e.g. primary lateral sclerosis, are really very rare)

Clinical features

  • It is often said that 1/3 will present with bulbar symptoms; 1/3 with arm symptoms; 1/3 with leg symptoms
  • Weakness, wasting, cramps, fasciculations (lower motor neuron); combined with brisk reflexes (upper motor neuron)
    • Disturbed speech/swallowing (dysarthria/dysphagia)
  • No sensory involvement
  • Cognitive impairment and dementia is not uncommon

Investigations

  • Blood tests are usually normal (may have raised CK)
  • Imaging is also usually normal (should be performed if symptoms are localised to exclude other cause of neuropathy)
  • Electromyography can reveal diagnostic features of denervation and reinnervation

Management/Prognosis

  • MND progresses often rapidly and, as pathology spreads/worsens, subsequent respiratory depression is eventually fatal
    • usually 18-30 months after diagnosis
  • Riluzole can be used to extend life expectancy BUT patients are often disabled at this stage and many patients opt not to take this
  • A multidisciplinary team involving physio, OT, SALT is important in managing patients with ALS/MND
  • Later on in the disease, non-invasive ventilation and percutaneous gastrostomy feeding may improve quality of life
    • Palliative care should be discussed
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