Motor neuron disease

The motor neuron diseases (MNDs) are a group of progressive neurological disorders of unknown cause in which there is degeneration of cells called motor neurons. The motor neurons in the spinal cord and cranial nerve nuclei and pyramidal neurons in the motor cortex are affected.

Classification

  • Amyotrophic lateral sclerosis (ALS)
  • Progressive bulbar palsy
  • Progressive muscular atrophy (PMA)

The major site of motor neuron degeneration classifies the disorders.

Amyotrophic lateral sclerosis (ALS) is the most important of MNDs and is caused by degenration of motor neurons at all levels of the CNS. It affects both upper and lower motor neurons and presents as combination of distal and proximal muscle-wasting and weakness with fasciculation. The reflexes are exaggerated with extensor plantar.

Progressive bulbar palsy, also called progressive bulbar atrophy, affects the lower motor neurons of the brainstem. In PMA there occurs early involvement of tongue, palate and pharyngeal muscles causing slurred speech and difficulty in chewing and swallowing.

Progressive muscular atrophy (PMA) is marked by slow but progressive degeneration of only the lower motor neurons. It largely affects men, with onset earlier than in other MNDs. Weakness is typically seen first in the hands and then spreads into the lower body, where it can be severe. Other symptoms may include muscle wasting, clumsy hand movements, fasciculations, and muscle cramps. The trunk muscles and respiration may become affected. Exposure to cold can worsen symptoms. The disease develops into ALS in many patients.

Treatment

Glutamate antagonist, riluzole has recently shown to have modest effect in prolonging survival of people with MND. However, the economics of its use have yest to be fully assessed. Also agents such as nerve growth factor (NGF) show promise.



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