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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. Lower motor neuron lesion

Symptoms

  1. Muscle paresis or paralysis
  2. fibrillations
  3. fasciculations
  4. hypotonia or atonia
  5. 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

  1. Myasthenia gravis � synaptic transmission at motor end-plate is impaired
  2. Muscular dystrophy � contraction of muscle is impaired due to a cellular defect