LMN, Lower Motor Neuron

Clinic

• LMNS = Lower motor neuron lesion = Lower Motor Neuron Syndrome
• It is a lesion which affects nerve fibers traveling from the lower motor neuron(s) in the anterior horn/anterior grey column of the spinal cord, or in the motor nuclei of the cranial nerves, to the relevant muscle(s).
• Flaccid paralysis accompanied by loss of muscle tone is the major characteristic of LMNS
• UMNS (Upper motor neuron lesion) often presents with spastic paralysis – paralysis accompanied by severe hypertonia.

Sign / Symptoms

• Muscle paresis or paralysis / Strength decreased
• Fibrillations
• Fasciculations
• Hypotonia or atonia
• Hypo reflexia
• Ascent extensor plantar reflex

Causes

• Trauma to peripheral nerves that serve the axons
• Disuse atrophy of the muscle occurs i.e., shrinkage of muscle fibre finally replaced by fibrous tissue (fibrous muscle)
• Guillain–Barré syndrome
• C. botulism
• Cauda equina syndrome
• ALS

Differential diagnosis

• Myasthenia gravis

• Hypotonia / Flaccidity
• Ipsilateral (same side) weakness of individual muscles.
• Atrophy
• Weak or absent deep tendon plantar reflexes and abdominal reflexes
• Fasciculations (Twitching)

Miasms

Viruses that selectively attack ventral horn cells such as

• WNE
• PLV