UMN Weakness Flashcards
responsible for voluntary control of movement
pyramidal tract
responsible for involuntary pathways for co-ordination of movement
extrapyramidal tracts
components of the pyramidal tract
corticobulbar and spinal
injury to the pyramidal tract results in…
UMN syndrome
what is the UMN?
located in brain or brainstem – spinal chord – innervates ventral horn
what is the LMN?
ventral horn to periphery
see homunculus
CTBs routes
CBTs arise lateral aspect of motor cortex → synapse on cranial nerves (CN 5,7,9,10,11,12) to control muscles of face + neck (face, jaw, swallow, tongue movts)
what does corticobulbar supply and what does the mean for symptoms if lesion?
Bilateral CN nuclei - unilateral CBT lesion gives mild muscle weakness
EXCEPT
CN 7 = paralysis of contralateral Lower face - UMN lesion
CN 12 = UMN lesion → paralysis of contralateral genioglossus → deviation of the tongue towards contralateral side
how to clinically assess a weak patient?
- MRC grading
- doing what they say, movement and maintaining posture e.g. outstretched arms
Spasticity
velocity-dependent increase in a muscle’s resistance to a passive stretch. Slow passive movements of the arms or legs will not elicit the increased resistance. Brisk stretches of muscles will cause an abrupt increase in tone followed by a decrease in muscular resistance with continued stretch. This phenomenon is called clasp-knife rigidity. The antigravity muscles of the arms and legs are most affected. These include the flexors of the arms and the extensors of the leg. Because of the decreased modulation of spinal reflexes in UMN syndrome, patients will often exhibit flexor and extensor spasms.
Clonus
Clonus is a sequence of rhythmic, involuntary muscle contractions. These contractions occur at a frequency of 5 to 7 Hz and are a response to abruptly applied stretch stimuli. Clonus is most easily elicited at the ankle with brisk dorsiflexion and plantar-flexion movements. Clonus can also be observed during voluntary movement or through cutaneous stimulation.
Reflexes
Hyperreflexia of deep tendon reflexes
Patients can be seen to have abnormally brisk reflexes which are due to decreased modulation by descending inhibitory pathways. Radiation of reflexes is a regular observation with the hyperreflexia of UMN lesions. For example, tapping of the supra-patellar tendon would elicit a knee-jerk reflex.
Hyporeflexia of superficial reflexes
The superficial abdominal reflex and the cremasteric reflex are seen to be decreased or abolished following UMN lesions. The superficial abdominal reflex is the tensing of abdominal by stroking the overlying skin while the cremasteric reflex is the elevation of the scrotum in response to stroking the medial thigh.
Pseudo-bulbar palsy
As previously stated, most cranial nerves have bilateral innervation from the brain with the exception of CN VII and CN XII. The muscles of cranial nerves with bilateral innervation include the eyes, jaw, pharynx, upper face, larynx, and neck. These muscles would only show deficits with bilateral UMN lesions. Bilateral damage of UMN’s to cranial nerves is known as a pseudobulbar palsy. Slurred speech is often the first presenting symptom. Other characteristic deficits include dysphagia, dysarthria, brisk jaw jerk, spastic tongue, and pseudobulbar affect.
Spinal shock
Spinal shock refers to the period of acute flaccid paralysis following spinal cord injury.
Hypotonia and hyporeflexia are the most characteristic symptoms.
The paralysis is most evident in the arms and legs with preservation of truncal musculature.
The duration can range from a few days to weeks after which spasticity and hyperreflexia replace the prior symptoms.
The symptoms of spinal shock are most pronounced with lesions of the spinal cord versus cerebral lesions.
once assessed as weak then what?
what type of weakness
Disuse atrophy
increased tone / spasticity
increased reflexes
clonus
plantar response
UMN lesion
atrophy
fasiculations
normal or reduced reflexes
absent clonus
decreased plantar
LMN lesion
pattern that is confined to nerve to root and bilateral proximal muscles
LMN pattern
pattern that extensors of arm and flexors of leg and anti-gravity muscles
UMN pattern
PATTERN PICS
Clinical assessment of the weak patient
- are they weak
- type of weakness
- pattern of distribution
- additional neuro signs
- causes + Ddx
localised cognitive functions
- language
- reading
- writing
- calc
- visuospatial
distributed cognitive functions
- arousal
- memory
- personality
- behaviour
