UMN + LMN

Question 1

What part of the nervous system does UMN and LMN affect?

Answer 1

UMN= CNS i.e. efferents with cell bodies in higher centres 
LMN= PNS i.e. efferents with cell bodies in spinal motor nucleus or CN motor nucleus

Question 2

What are the causes of UMN lesions?

Answer 2

Stroke
Traumatic brain injury
Spinal cord injury
Multiple sclerosis

Question 3

What is the reasoning behind UMN signs?

Answer 3

UMN normally act as inhibitors of primitive LMN actions

== loss of UMN means signs related to excessive LMN activity

Question 4

What are the signs associated with UMN lesions?

Answer 4

Rigidity and hypertonia= LMN constantly activated w/o inhibition

Hyperflexia= hyper-sensitised reflexes i.e. increased activity of gamma-MN means there’s increased tension in intrafusal fibres which means they are more sensitive for detecting changes in muscle length

Minimal atrophy= no loss of neurotrophic factors

Absent fasciculations

Hemiparesis (one side)

Paraparesis (LL)

+ve Babinski reflex= plantar extension rather than flexion in response to stroking of sole of foot i.e. due to CST lesion meaning loss of excitation of distal flexors so extensors dominate

Clonus= involuntary rhythmic muscle contractions

Chorea= uncoordinated and involuntary movements

Question 5

What is spastic paraparesis? What are examples of conditions that can cause it?

Answer 5

Bilateral UMN signs associated with legs

Causes:

• MS i.e. MS plaques on the brain
• cervical myelopathy i.e. narrowing of spinal column
• malignancy
• MND i.e. can present with mixed UMN + LMN signs
• syringomyelia i.e. out pouch of fluid compressing SC
• vit B12 deficiency
• HIV myelopathy

Question 6

What are the most common causes of peripheral nerve damage/LMN damage?

Answer 6

Diabetes 
Alcoholic peripheral neuropathy 
B12 deficiency 
Drugs 
Guillain-Barré syndrome

Question 7

What are the common signs associate with LMN lesion?

Answer 7

Flaccid/weakness

Atonia= loss of alpha-MN means loss of mechanism to stimulate extrafusal fibres= decreased tone

Areflexia = loss reflex arc due to loss of myotactic stretch efferent

Atrophy= loss of neurotrophic factors

Fasciculations= spontaneous firing of alpha-MN

Sensory disturbances= peripheral spinal nerves are mixed nerves meaning that some sensory function also likely to be lost

Question 8

How can you differentiate between Bell’s palsy and complete CNVII palsy? What is the pathology causing each of these?

Answer 8

Bell’s = NOT forehead sparing due to loss of bilateral innervation of forehead as LMN contain contributions from both sides of cortex

Stroke= loss of unilateral UMN so the contralateral muscles of facial expression lost but part of bilateral innervation of frontalis remains to enable wrinkling of forehead

Question 9

What are the different parts of the PNS which can be involved in LMN lesion?

Answer 9

NMJ

Anterior horn

Nerve root

Plexus

Nerve

Muscle

Question 10

What sign indicates anterior horn cell problems and what condition is it a red flag sign for?

Answer 10

Wide spread fasciculations

MND= fasciculations in context of UMN signs is a red flag for MND i.e. anterior horn junction affected meaning MND has mixed presentation of signs

Question 11

What is radiculopathy and what is the most common radiculopathy? How is it differentiated from single nerve damage?

Answer 11

Symptoms associated with nerve root damage

Sciatica i.e. unilateral pain, pins + needles and numbness in LL

effects a larger somatic and muscular distribution than single nerve

Question 12

What causes Guillain-Barré syndrome and how would someone suffering present?

Answer 12

AI condition post-bacterial/viral infection where cross-sensitivity of infection leads to degeneration of axons in peripheral nerves
-ascending condition= distal to proximal

Would present with finger dysesthesia and proximal leg weakness 2-4 weeks post-infection

Question 13

What are the 3 most common causes of NMJ disorders? Briefly describe their pathology.

Answer 13

Myasthenia gravis
-auto-antibodies attack AchR= decreased firing due to decreased receptors on post-synaptic membrane

Lambert-Eaton syndrome
-auto-antibodies targeting pre-synaptic calcium channels causing decreased Ach release from pre-synaptic neurones

Botulism
-decreased Ach release from pre-synaptic terminals

Question 14

What are the characteristic symptoms of NJM disorder? What is the key difference with Lambert-Eaton syndrome that can act as differential?

Answer 14

Proximal symptoms
-weakness in shoulder and thighs
-numbness and tingling
-difficulty walking due to proximal leg weakness
Fatigable= increased weakness with use due to using up Ach
Muscle loss i.e. disuse or because of de-innervation

Muscle weakness decreases with use due to Ach build up in NJM to enable momentary increase in strength

Question 15

What are indicators that deficits in function is due to a muscular problem? What causes muscular problems?

Answer 15

Proximal weakness i.e. shoulder or hip = feel HEAVY

No sensory impairment

Cuase:

• inflammation i.e. dermatitis or polymotic
• hypothyroidism
• flu
• drugs

Question 16

What is the presentation of someone with radial nerve palsy? What are the most common causes?

Answer 16

Wrist drop= loss of extensor muscle innervation in posterior compartment of arm

Loss of digit extension

Loss of sensation between dorsal aspect of 1st and 2nd metacarpal

CAUSE:

• compression of radial nerve in axilla= Saturday night palsy or due to crutches
• fractured humerous

Question 17

What are the signs of median nerve palsy?

Answer 17

Denervation of flexors and pronators of forearm i.e. forearm in constant supinated position

Loss of thumb opposite to 5th digit

Hand of Benediction when patient tries to make a fist
I.e. 1st 3 digits unable to flex due to 2 lateral lumbrical muscles being paralysed

Median claw when patient tries to extend fingers

Question 18

What are causes of median nerve palsy and what are the characteristic features of some of these causes?

Answer 18

Supracondylar fracture

Carpal tunnel syndrome

• tingling in 1st 3.5 digits
• weakness in addiction of thumb
• thenar eminence wastage

Question 19

What are the signs of ulnar nerve palsy? What are the causes?

Answer 19

Ulnar claw 
Wasting in dorsal interosseous but thenar eminence spared 
Decreased grip strength 
Clumsiness
Sensory loss= 1/2 of 4th + 5th digit 

CAUSES:
Cubital tunnel syndrome i.e. fractures or dislocations of elbow OR repetitive strain
Ulnar entrapment in Guyon’s canal