UMN/LMN Lesions

Question 1

Where is the cell body LMN/UMN?

Answer 1

LMN - ventral horn spinal cord/cranial nerve nuclei

UMN - cerebral motor cortex or brain stem

Question 2

Distribution of signs in UMN/LMN lesion?

Answer 2

LMN - signs have distribution of peripheral nerve affected

UMN - widespread signs e.g. hemiparesis

Question 3

Paralysis type in UMN/LMN lesion?

Answer 3

LMN - flaccid paralysis (atonia)

UMN - spastic paralysis (increased tone)

Question 4

LMN signs?

Answer 4

Flaccid paralysis
Weakness
Fasciculations (brief spontaneous contraction of muscle fibres causing flicker under skin)
Muscles wasting, atrophy
Hypotonia
Hyporeflexia

Question 5

UMN Signs?

Answer 5

Spastic paralysis
Weakness
No fasciculation/wasting until disuse atrophy
Hypertonia
Hyperreflexia
Clasp knife reflex
Plantar extensor reflex (Babinski’s sign)
Clonus (spasm - repeated, rhythmic contraction)

Question 6

What signs are indicative of lesions in the extra-pyramidal system?

Answer 6

Generation of unwanted, uncontrollable movements, or aberrant reflexes?

Question 7

Causes of LMN/UMN lesion?

Answer 7

LMN - peripheral neuropathy - MND/diabetes, traumatic injury

UMN - stroke, spinal cord injury