LMN, Lower Motor Neuron

Clinic

• LMN nerve fibers traveling from the lower motor neuron(s) in the Anterior horn of the spinal cord, or in the motor nuclei of the cranial nerves, to the relevant muscle(s).
• UMN (Upper motor neurons) are often efferent nerve fibers that carry signals from the cerebral cortex to either the brain-stem or the spinal cord.
• LMN lesions are characterized Hypotonia or flaccid opposed to UMN lesions which present with hypertonia or spastic paralysis.

Entities

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

Causes

Dynamic	Miasms	Static
Guillain–Barré syndrome C. botulism ALS Progressive muscular atrophy Monomelic amyotrophy	Viruses that selectively attack ventral horn cells such as WNE PLV	Trauma to peripheral nerves Cauda equina syndrome

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)