Lower motor neuron lesion

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.

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