Lower motor neurone lesion

Lower motor neurone lesion


Caption = Lower motor neuron in red
DiseasesDB = 22143
ICD10 =
ICD9 =
MedlinePlus =
eMedicineSubj =
eMedicineTopic =
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A lower motor neuron lesion is a lesion which affects nerve fibers travelling 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 neurone lesion is flaccid paralysis - paralysis accompanied by muscle loss. This is in contrast to a upper motor neurone lesion, which often presents with spastic paralysis - paralysis accompanied by severe hypertonia.


* Muscle paresis or paralysis
* fibrillations
* fasciculations
* hypotonia or atonia
* Areflexia or hyporeflexia

The Babinski reflex, if present will be normal. Muscle paresis/paralysis, hypotonia/atonia, and hyporeflexia/areflexia are usually seen immediately following the insult. Muscle wasting, fasciculations and fibrillations are typically signs of end-stage muscle denervation and are seen over a longer time period. Fasciculations are spontaneous muscle contractions that are visible and have a characteristic pattern on EMG. They are due to increased alpha motor neuron activity, but are not specific for lower motor injury. Fibrillations cannot be seen on physical examination. They are spontaneous electrical impulses and are a result of the muscle denervation. Fibrillations do not occur in healthy patients. Another feature is the segmentation of symptoms - only muscles innervated by the damaged nerves will by 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.

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

* http://library.med.utah.edu/neurologicexam/html/motor_anatomy.html#06

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