Lecture 27: Sensation Flashcards
Where in the nervous system will a lesion give a sensory loss?
- Brain
- Spinal cord
- Peripheral (sensory) nerves
Describe the pathway projecting from the thalamus to the CNS:
Pathways project from the thalamus to the CNS via the corona radiate, therefore, lesions occurring within these points will causes sensory symptoms
Write some notes on multiple sclerosis relating it to sensory deficits:
- Results in inflammatory lesions that can occur in the spinal cord, white matter tracts, optic n. etc
- Focal neurological deficits, subacute onset
- Sensory symptoms often first symptom
What is the ‘sensory level’ when it comes to spinal cord lesions:
Sensory level refers to feeling above not below
Why must you test sensory symptoms with a pin?
With spinal cord lesions, because the anatomy of the tracts you can have preserved dorsal columns (fine touch, pressure, vibration) and lost anterior spinothalamic (pain, temp) which can only be tested for with a pin!
What are possible causes of bilateral symptoms below lesion level?
- Complete spinal cord lesion (i.e paralysis)
- Anterior cord or central cord stroke, cancer
- Hemicord lesion
Write some notes on anterior cord lesion:
Less obvious diagnosis because posterior columns are preserved i.e ant. spinal cord artery occlusion -> ant. cord infarct.
i.e test with pin because loss of motor symptoms but preserved fine touch might mislead.
Write some notes on central cord stroke/cancer:
Central i.e central cord dilation or stroke
- Spares posterior columns and maybe power i.e syringomyelia
Write some notes on hemi-cord injury:
Hemi-cord (Brown sequard lesion)
- Different modalities on each side
- > Pin prick abnormal on other side b/c decussation immediately
- > Position, vibration (and strength) on same side
What are 3 patterns of peripheral nerve lesions:
- Mononeuropathy
- Mononeuropathy multiplex
- Polyneuropathy (Systemic)
Write some notes on mononeuropathies:
Due to a lesion in an individual peripheral nerve
- > Sensory loss in skin within the nerves distribution
- > Also see weakness in the muscles innervated by that particular nerve
What are common examples of mononeuropathies:
Carpal tunnel syndrome
Radial palsy
Ulnar neuropathy
Common peroneal nerve palsy
What is carpal tunnel syndrome?
Median nerve is compressed at the wrist, resulting in numbness or pain
Write some notes on mononeuritis multiplex and some examples:
Due to disease of the peripheral nerves
Vasculitis
- Micro polyangiitis
(Just touched on):
Inflammatory disease
- Multifocal motor neuropathy with conduction block
Genetic
- Hereditary neuropathy with susceptibility to pressure palsies
Write some notes on peripheral polyneuropathies:
Due to disease of the peripheral nerves
- Length dependent
- Can be motor and sensory involvement
- Motor involvement alone
- Sensory involvement alone (glove and stocking)
Most common cause of sensory loss.
Describe how different peripheral nerves cause different peripheral polyneuropathies:
Different pathologies cause different sorts of nerve fibres to be involved
- Small unmyelinated axons
- Large myelinated fibres
- Myelin laters themselves affected
Whats an example of peripheral polyneuropthy and how does the injury develop over time?
Peripheral polyneuropathy
- i.e diabetes mellitus, alcohol
- > Small unmyelinated fibres
- > Starts in nerves with longest axons i.e to feet
- Insidious onset sensory symptoms and pain
- > Initially in feet
- > Then gradually ascends to lower limbs
- > And eventually symptoms start in the hands
Whats an example of a demyelinating neuropathy:
Guillian barre syndrome
Write some notes on radiculopathy:
- Lesion in a single nerve root
- Sensory loss in the skin supplied by that nerve root
- Also get:
- > Weakness in muscles supplied by that nerve root
- > Loss of reflexes supplied by that nerve root
Is examination of sensation easy?
- Most difficult and unreliable part of the examination
- Depends on patient cooperation
- The approach to examining sensation depends on the symptoms and other neurological signs
Write some notes on examination of sensation:
- Largely directed by history
- Leave till end:
- > Mental state
- > Cranial nerves
- > Power, tone, coordination
- > Reflexes
- By then you might have an idea of what you will find
Describe some patterns of sensory loss:
Numbness->Localisation
Small localised -> Local nerve
Glove and Stocking -> Peripheral neuropathy
Dermatome -> Nerve root
Large patch of limb -> Plexus or mutiple nerve roots
Whole of right arm and face -> L cortex or corona radiata
Pin prick / pain in arm -> Central cord in neck
Position sense at ankles -> Post. columns
R leg position, l leg pain -> Hemicord
R face and L arm -> R side pons
R hemi-anaesthesia -> L thalamus
What are some symptoms possible associated with sensory loss:
Upper motor neuron
Lower motor neuron
or just pure sensory ie diabetic peripheral neuropathy
What might indicate an upper motor neuron assocation?
- Weakness, increased tone and increased reflexes
- 1/2 body affected or spinal cord motor level
What might indicate a lower motor neuron assocation?
- Weakness, decreased tone and reflexes
- Nerve root or peripheral nerve distribution
What are the instruments used for each sense?
Light touch -> Cotton wool
Pain -> Safety pin
Vibration -> 128hz tuning fork
Joint position -> Passive joint movement
What are some things to look out for with soft touch and pin prick?
- Look for absolute abnormalities i.e patient cant feel the stimulus or cant perceive difference between sharp and dull
- Also enquire about qualitative changes
