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neurodegenerative diseases affecting motor neurons

Tuesday 14 April 2009

Neurodegenerative diseases affecting motor neurons are a group of inherited or sporadic diseases that, in variable degrees of severity, affect:

- lower motor neurons in the anterior horns of the spinal cord
- lower motor neurons in certain cranial nerve motor nuclei (V, VII, IX, XII) but not those that control eye movements (III, IV, VI)
- upper motor neurons (Betz cells) in the motor cortex

The disorders occur in all age groups, and the course of the illness is extremely variable, ranging from slowly progressive or nonprogressive to rapidly progressive and fatal in a period of months or a few years.

Denervation of muscles from loss of lower motor neurons and their axons results in muscular atrophy, weakness, and fasciculations.

The clinical manifestations include paresis, hyperreflexia, spasticity, and extensor plantar responses (Babinski sign).

Sensory systems and cognitive functions are unaffected, but types with dementia do occur.

Types

- amyotrophic lateral sclerosis (ALS) (motor neuron disease)
- bulbospinal atrophy (Kennedy syndrome)
- spinal muscular atrophy