Neuro Examination Findings & Visual Fields

Question 1

Explain the pathophysiology behind UMN and LMN lesion signs

Answer 1

If we damage UMNs in the CNS, there is a LOSS of INHIBITION leading to constant contraction of muscles.

In contrast, if LMNs are damaged, we have a LOSS of ACTIVATION of muscles (loss of signals to the muscles to contract)

Question 2

How do UMN lesions present on examination?

Answer 2

Minimal disuse atrophy or contractures
Increased tone (spasticity/rigidity) +/- ankle clonus
Pyramidal pattern of weakness (extensors weaker than flexors in arms, and vice versa in legs)
Hyperreflexia
Upgoing plantars (Babinski sign)

Question 3

How do LMN lesions present on examination?

Answer 3

Marked atrophy
Fasciculations (you are so Floppy you Fasiculate)
Reduced tone
Variable patterns of weakness
Reduced or absent reflexes
Downgoing plantars or absent response

Question 4

What are the sites of damage for UMN and LMN lesions?

Answer 4

UMN: Cerebral hemispheres, cerebellum, brainstem, spinal cord

LMN: Anterior horn cell, motor nerve roots, peripheral motor nerves

Question 5

How do UMN v LMN lesions present on inspection?

Answer 5

UMN: No fasciculations or significant wasting (however there may be some disuse atrophy or contractures)

LMN: Wasting and fasciculation of muscles

Question 6

How may UMN v LMN present in terms of power?

Answer 6

UMN: Reduced with pyramidal pattern of weakness (extensors weaker than flexors in arms, and vice versa in legs)

LMN: Reduced in distribution of affected motor root/nerve

Question 7

Give some examples of conditions that may cause UMN lesions

Answer 7

Ischaemic or haemorrhagic stroke (including brainstem strokes)

Amyotrophic lateral sclerosis (MND)

Multiple sclerosis

Question 8

How may UMN v LMN present in terms of reflexes?

Answer 8

UMN: Exaggerated or brisk (hyperreflexia)
Plantar reflex is upgoing/extensor (Babinski positive)

LMN: Reduced or absent (hyporeflexia or areflexia)
Plantar reflex is normal (downgoing/flexor) or no movement

Question 9

Give some examples of conditions that may cause LMN lesions

Answer 9

Peripheral nerve trauma/compression
Spinal muscular atrophy
Amyotrophic lateral sclerosis
Guillain-Barré syndrome
Poliomyelitis

Question 10

Draw out the visual fields

Answer 10

Question 11

Outline the visual pathway

Answer 11

retina, optic nerve, optic chiasm, optic radiations, and the visual centre in the occipital lobe

Question 12

What is caused by a lesion at point 1 in the visual pathway?

Answer 12

Question 13

What is caused by a lesion at point 2 in the visual pathway?

Answer 13

Question 14

What is caused by a lesion at point 3 in the visual pathway?

Answer 14

Question 15

What is caused by a lesion at point 4 in the visual pathway?

Answer 15

Question 16

What is caused by a lesion at point 5 in the visual pathway?

Answer 16

Question 17

What type of visual field defect is caused by damage to the optic nerve?

Answer 17

Ipsilateral monocular blindness

Question 18

Give some examples of lesions that may form on the optic nerve

Answer 18

Optic neuritis
Optic atrophy
Amaurosis fugax
Retrobulbar optic neuropathy
Trauma

Question 19

What type of visual field defect is caused by lesions of the optic chiasm?

Answer 19

Bitemporal hemianopia

At the optic chiasm, fibres from the nasal half of the retina (corresponding to the temporal visual field) decussate

Question 20

Give some examples of lesions that can be found on the optic chiasm

Answer 20

Pituitary adenoma

Suprasellar aneurysm

Question 21

What type of visual field defect is caused by lesions of the optic tract?

Answer 21

Contralateral homonymous hemianopia

Question 22

What type of visual field defect is caused by lesions of the optic radiations ?

Answer 22

Contralateral homonymous quadrantanopia

Question 23

What can cause damage to the optic tracts and the optic radiations?

Answer 23

MCA stroke
Tumours

Question 24

What type of visual field defect is caused by lesions of the occipital cortex?

Answer 24

Contralateral homonymous hemianopia with macular sparing

Question 25

What can cause damage to the occipital cortex?

Answer 25

PCA stroke
Trauma

Question 26

Presence of a left homonymous hemianopia means there is a lesion where?

Answer 26

Lesion of right optic tract / optic radiation

incongruous defect (different between the eyes): optic tract
congruous defect (the same between the eyes): optic radiation

Question 27

How can you tell the location of the lesion that causes a Homonymous quadrantanopia?

Answer 27

superior: lesion of the inferior optic radiations in the temporal lobe (Meyer’s loop)

inferior: lesion of the superior optic radiations in the parietal lobe

mnemonic = PITS (Parietal-Inferior, Temporal-Superior)

Question 28

Bitemporal hemianopias are commonly caused by lesions of the optic chiasm.

How can you tell where in the chiasm the causative lesion may be?

Answer 28

upper quadrant defect > lower quadrant defect = inferior chiasmal compression, commonly a pituitary tumour

lower quadrant defect > upper quadrant defect = superior chiasmal compression, commonly a craniopharyngioma