Diagnosing LMN disorders

Question 1

How will damage to LMN present?

Answer 1

• wasting
• decreased tone
• decreased reflexes
• extensor plantar response

Question 2

How will damage to UMN present?

Answer 2

• no wasting
• increased tone
• increased reflexes (lose inhibition of reflexes)
• increased plantar response
  (brisk reflexes and spasticity)

Question 3

What are radiculopathies?

Answer 3

damage to nerve root

Question 4

What are neuropathies?

Answer 4

damage to peripheral nerve

Question 5

What are myopathies?

Answer 5

damage to muscle fibres

Question 6

How do myopathies present?

Answer 6

• proximal weakness
• symmetrical weakness
• Can be painful
• reflexes spared until late
• limited muscle wasting until late in disease

Question 7

How do NMJ disorders present?

Answer 7

• fatiguable muscle weakness (gets worse on repetition)
• involves extra ocular muscles (ophthalmoplegia, ptosis and diplopia)
• involves bulbar muscles (chewing and swallowing)

Question 8

What are polyneuropathies?

Answer 8

diffuse damage of peripheral nerves (mononeuropathy is one nerve)

Question 9

How do polyneuropathies present?

Answer 9

• length dependent (distal nerves affected first)
• symmetrical
• weakness (can also have sensory loss)
• reflexes absent
• distal wasting

Question 10

How do MNDs present?

Answer 10

- Painless progressive weakness and 
wasting
- Eye movements normal
- Sensation normal
- UMN and LMN signs
- present with respiratory muscle weakness

Question 11

What are the important questions to ask in LMN lesion?

Answer 11

1) pattern of weakness (proximal v distal)
2) speed of onset
3) pain?
4) sensory loss?
5) symptoms of respiratory
6) muscle weakness

Question 12

What LMN disorders present with pain?

Answer 12

radiculopathy
some peripheral neuropathies
some muscle diseases
(no pain in MND or NMJ)

Question 13

What disorders will present with sensory loss?

Answer 13

peripheral neuropathies
radiculopathies
not in muscle, NMJ or MND

Question 14

What should examination include for LMN lesion?

Answer 14

• wasting (MND or peripheral nerve)
• fasiculations (possible MND or proximal nerve)
• look at trunk and back
• check feet (hammer toes or pes cavus possibly peripheral neuropathy)

Question 15

proximal symmetrical weakness?

Answer 15

myopathy

Question 16

Distal symmetrical?

Answer 16

polyneuropathy

Question 17

affecting one nerves muscles?

Answer 17

mononeuropathy

Question 18

affecting one spinal root muscles?

Answer 18

radiculopathy

Question 19

absent/ reduced reflexes?

Answer 19

peripheral neuropathy

Question 20

normal/reduced reflexes?

Answer 20

myopathy

Question 21

increased reflexes with other LMN symptoms?

Answer 21

MND

Question 22

distal symmetrical sensory loss?

Answer 22

peripheral neuropathy

Question 23

sensory loss of one nerve area?

Answer 23

mononeuropathy

Question 24

What are the possible investigations for LMN lesions?

Answer 24

CK blood test
neurophysiology 
muscle biopsy 
MRI spine 
Muscle MRI (reveal pattern of muscle wasting) 
Genetic testing

Question 25

What are the pathological causes of increased Creatine Kinase?

Answer 25

+ 10,000 = rhabdomyolysis, muscular dystrophy

+ 1000 = many myopathies cause

Question 26

How can muscle biopsy help diagnose LMN lesions?

Answer 26

• myopathy vs neuropathy
• inflammation
• metabolic myopathies
• mitochondrial myopathies
• specific features of genetic myopathies

Question 27

What is a common hereditary peripheral neuropathy?

Answer 27

Charcot Marie Tooth