| Lower motor neuron lesion | |
| Classification and external resources | |
 Lower motor neuron in red |
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| DiseasesDB | 22143 |
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| eMedicine | / |
A lower motor neuron lesion is a lesion which affects nerve fibers traveling from the anterior horn of the spinal cord to the relevant muscle(s) -- the lower motor neuron.
One major characteristic used to identify a lower motor neuron lesion is flaccid paralysis - paralysis accompanied by muscle loss. This is in contrast to a upper motor neuron lesion, which often presents with spastic paralysis - paralysis accompanied by severe hypertonia.
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Symptoms
- Muscle paresis or paralysis
- fibrillations
- fasciculations
- hypotonia or atonia
- Areflexia or hyporeflexia
The extensor Babinski reflex is usually absent. Muscle paresis/paralysis, hypotonia/atonia, and hyporeflexia/areflexia are usually seen immediately following an insult. Muscle wasting, fasciculations and fibrillations are typically signs of end-stage muscle denervation and are seen over a longer time period. Another feature is the segmentation of symptoms - only muscles innervated by the damaged nerves will be symptomatic.
Etiology
Most common causes of lower motor neuron injuries are trauma to peripheral nerves that sever the axons and poliomyelitis - a virus that selectively attacks ventral horn cells. disuse atrophy of the muscle occurs i.e,shrinkage of muscle fibre finally replaced by fibrous tissu(fibrous musle)
Differential Diagnosis
- Myasthenia gravis - synaptic transmission at motor end-plate is impaired
- Muscular dystrophy - contraction of muscle is impaired due to a cellular defect
External links
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