|Lower motor neuron lesion
|Classification and external resources
Lower motor neuron in red
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 an upper motor neuron lesion, which often presents with spastic paralysis – paralysis accompanied by severe hypertonia.
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.
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 tissue (fibrous muscle) Other causes include Guillain-Barré syndrome, C. botulism, polio, and cauda equina syndrome.
Differential Diagnosis 
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