Progression and Potential Complications of Motor Neuron Diseases


What are motor neuron diseases?

Motor neuron diseases (MNDs) are progressive neurological conditions that occur when motor neurons, or nerve cells that control muscle movement, become damaged and die.‌‌ This affects skeletal muscle activity, such as walking, speaking, swallowing and breathing.

Progression of motor neuron diseases

In most cases, muscle weakness from motor neuron diseases gradually worsens, and unfortunately, some MNDs are fatal. Progression of motor neuron diseases varies depending on the specific type of disease.

  • Amyotrophic lateral sclerosis (ALS)
    ALS is one of the most rapidly progressive motor neuron diseases. It typically progresses from muscle weakness to paralysis to respiratory failure within three to five years. However, some individuals with ALS live 10 years or longer.
  • Primary lateral sclerosis (PLS)
    Symptoms of PLS typically start in the legs, followed by the torso, arms, and hands, and finally the mouth and throat. It progresses much more slowly than ALS. Primary lateral sclerosis is not fatal; however, it may progress to ALS.
  • Progressive bulbar palsy (PBP)
    Early symptoms of PBP include weakness of the mouth and throat muscles. Symptoms eventually become more widespread, affecting the arms or legs. PBP may also progress to ALS.
  • Progressive muscular atrophy (PMA)
    PMA typically starts with weakness in the hands. Weakness then spreads to the lower body. This progression often occurs slowly; however, in some cases, PMA progresses to ALS.
  • Kennedy’s disease
    Tremors of outstretched hands, muscle cramps during physical activity, and twitching of the muscles are typically the first symptoms of Kennedy’s disease. Weakness in the muscles of the face, jaw and tongue may also occur, which affects speaking, chewing and swallowing. As Kennedy’s disease progresses, which usually happens very slowly, weakness begins to affect the pelvis and shoulders, eventually spreading to the legs and arms. Because the progression of Kennedy’s disease occurs very slowly, many with the disease have a normal life expectancy.

Potential complications of motor neuron diseases

Potential complications of motor neuron diseases include, but are not limited to, the following:

  • Difficulty swallowing, which can lead to poor nutrition and weight loss
  • Choking or breathing in food or fluid
  • Pneumonia
  • Pressure sores
  • Difficulty breathing or respiratory failure
  • Injuries from falls
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