Localizing the lesion Flashcards
Describe the corticospinal tracts
Carry motor information from the precentral gyrus of the frontal cortex up to synapse with anterior horn cells in the spinal cord
Describe the pattern of weakness in an UMN lesion
Pyramidal pattern
Arm - extensors are weaker
Leg - flexors are weaker
Where does spasticity develop in an UMN lesion
Spasticity occurs in the stronger muscle groups (arm - flexors, leg - extensors)
How does spasticity manifest?
Increased tone that is velocity dependent (The faster you move patients muscles, greater the resistance till it suddenly gives way like a clasp knife)
Does muscle wasting occur with an UMN lesion?
No - disuse atrophy however may occur
Describe the reflexes in an UMN lesion
Hyperreflexia
Positive Babinski sign - upgoing plantars
Clonus (elicited by rapidly dorsiflexing the foot, <3 rhythmic downward jerks of the foot are normal)
What can UMN mimic in the first few hours?
LMN
Where is the damage in an UMN lesion
Anywhere in the corticospinal tract
Where is the damage in a LMN lesion
Anywhere from the anterior horn cells distally, including nerve roots, plexuses and peripheral nerves
What does the pattern of weakness in a LMN lesion correspond with?
The muscles supplied by the involved neurons
Describe the tone in muscles when a LMN lesion is present?
Hypotonia/flaccidity - the limb feels soft and floppy, providing little resistance to passive stretch
Describe the signs present in the muscles in LMN lesions
Wasting and fasciculations
What are fasciculations
spontaneous involuntary twitching
Describe the reflexes in a LMN lesion
Hyporeflexia (reduced/absent)
Plantars remain flexor
What is the main differential of a LMN lesion
Primary muscle disease
How do you distinguish between primary muscle disease and a LMN lesion
In LMN lesion - symmetrical loss, reflexes reduced/absent and there is no sensory component
List some conditions which may present with mixed UMN and LMN signs
MND
B12 deficiency
Taboparesis
How do pain and temperature sensations travel?
Along small fibres in peripheral nerves and the anterolateral (spinothalamic) tracts in the cord and brainstem
How does joint position and vibration sense travel?
In large fibres in peripheral nerves and the large dorsal columns of the cord
Which classification chart is used to grade power?
MRC classificaiton
Describe the MRC classification
Grade 0 - No muscle contraction
Grade 1 - Flicker of contraction
Grade 2 - Some active movement
Grade 3 - Active movement against gravity
Grade 4 - Active movement against resistance
Grade 5 - Normal power (allow for age)
Where would the lesion be in a cranial nerve palsy contralateral to a hemiplegia?
Brainstem injury on the side of the cranial nerve palsy
Describe the signs of a cord lesion
LMN signs at the level of the lesion
UMN signs below the level of the lesion
Sensory level is the hallmark
What picture do hemi-cord lesions present
Brown sequard
Describe the Brown sequard picture
Dorsal column loss (joint position sense and vibration) on the same side as the lesion Spinothalamic loss (pain and temperature) on the opposite side of the lesion
When might a dissociated sensory loss occur?
In cervical cord lesions
Describe a dissociated sensory loss
Loss of joint position and vibration sense without the loss of pain and temperature
What do peripheral neuropathies cause?
Distal weakness
How does the weakness in Guillian barre present?
Distal weakness which ascends over time
