Prognosis

Prognosis varies depending on the type of MND and factors such as the age of onset (1)

• PLS progress slowly
• ALS and some forms of spinal muscular atrophy (SMA) are fatal (2)
  
  
• ALS is a fatal disease
  • median survival is 3 years from clinical onset of weakness and most patients die of respiratory failure (1)
    • note though that about 15% of patients with ALS live 5 years after diagnosis, and about 5% survive for more than 10 years
    • longer survival is associated with:
      • a younger age at onset
      • male sex
      • limb (rather than bulbar) symptom onset
        
        
• slower progression occurs in regionally limited forms of motor neuron disease (i.e. brachial biplegia, lumbosacral biplegia, and progressive bulbar palsy [PBP])
  
  
• progressive muscular atrophy (PMA), distinct from classic ALS because of lack of upper motor neuron (UMN) findings, progresses at the same rate as classic ALS
  
  
• a slower rate of progression is seen in upper motor neuron -predominant ALS
  
  
• primary lateral sclerosis (PLS) - survival rate is much longer than ALS (measured in decades)

From the differential prognoses seen in motor neurone disease it seems that the loss of LMNs is a significant prognostic determinant.

Reference

1. Niedermeyer S, Murn M, Choi PJ. Respiratory Failure in Amyotrophic Lateral Sclerosis. Chest. 2019 Feb;155(2):401-408
2. Simon NG, Turner MR, Vucic S, et al. Quantifying disease progression in amyotrophic lateral sclerosis. Ann Neurol. 2014 Nov;76(5):643-57