Neuro Examination Findings & Visual Fields Flashcards
Explain the pathophysiology behind UMN and LMN lesion signs
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)
How do UMN lesions present on examination?
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)
How do LMN lesions present on examination?
Marked atrophy
Fasciculations (you are so Floppy you Fasiculate)
Reduced tone
Variable patterns of weakness
Reduced or absent reflexes
Downgoing plantars or absent response
What are the sites of damage for UMN and LMN lesions?
UMN: Cerebral hemispheres, cerebellum, brainstem, spinal cord
LMN: Anterior horn cell, motor nerve roots, peripheral motor nerves
How do UMN v LMN lesions present on inspection?
UMN: No fasciculations or significant wasting (however there may be some disuse atrophy or contractures)
LMN: Wasting and fasciculation of muscles
How may UMN v LMN present in terms of power?
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
Give some examples of conditions that may cause UMN lesions
Ischaemic or haemorrhagic stroke (including brainstem strokes)
Amyotrophic lateral sclerosis (MND)
Multiple sclerosis
How may UMN v LMN present in terms of reflexes?
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
Give some examples of conditions that may cause LMN lesions
Peripheral nerve trauma/compression
Spinal muscular atrophy
Amyotrophic lateral sclerosis
Guillain-Barré syndrome
Poliomyelitis
Draw out the visual fields
Outline the visual pathway
retina, optic nerve, optic chiasm, optic radiations, and the visual centre in the occipital lobe
What is caused by a lesion at point 1 in the visual pathway?
What is caused by a lesion at point 2 in the visual pathway?
What is caused by a lesion at point 3 in the visual pathway?
What is caused by a lesion at point 4 in the visual pathway?
What is caused by a lesion at point 5 in the visual pathway?
What type of visual field defect is caused by damage to the optic nerve?
Ipsilateral monocular blindness
Give some examples of lesions that may form on the optic nerve
Optic neuritis
Optic atrophy
Amaurosis fugax
Retrobulbar optic neuropathy
Trauma
What type of visual field defect is caused by lesions of the optic chiasm?
Bitemporal hemianopia
At the optic chiasm, fibres from the nasal half of the retina (corresponding to the temporal visual field) decussate
Give some examples of lesions that can be found on the optic chiasm
Pituitary adenoma
Suprasellar aneurysm
What type of visual field defect is caused by lesions of the optic tract?
Contralateral homonymous hemianopia
What type of visual field defect is caused by lesions of the optic radiations ?
Contralateral homonymous quadrantanopia
What can cause damage to the optic tracts and the optic radiations?
MCA stroke
Tumours
What type of visual field defect is caused by lesions of the occipital cortex?
Contralateral homonymous hemianopia with macular sparing
What can cause damage to the occipital cortex?
PCA stroke
Trauma
Presence of a left homonymous hemianopia means there is a lesion where?
Lesion of right optic tract / optic radiation
incongruous defect (different between the eyes): optic tract
congruous defect (the same between the eyes): optic radiation
How can you tell the location of the lesion that causes a Homonymous quadrantanopia?
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)
Bitemporal hemianopias are commonly caused by lesions of the optic chiasm.
How can you tell where in the chiasm the causative lesion may be?
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
