Neurolocalisation 1 - Spinal Cord and Peripheral Nerves Flashcards
- Upper motor neuron.
- Lower motor neuron.
- Travels w/in CNS from brain to synapse w/ circuits involving lower motor neuron.
In most instances, equates to brain, brainstem, spinal cord (CNS). - Projects outside CNS to synapse w/ muscle.
In most instances, equates to motor nerves (PNS).
*Peripheral nerves start in spinal cord, so spinal cord injury can give upper and lower motor neuron signs.
What if an UMN is damaged?
The distal portion (separated from the cell) degenerates.
UMN input mainly inhibitory, so reflex arcs become more excitable.
- existing reflexes stronger and easier to elicit.
- some normally inhibited reflexes become apparent.
- muscle tone increases.
Reduced movement (paresis) or no movement (plegia).
Disuse atrophy occurs w/ time.
What if a LMN is damaged?
Distal portion (separated from cell body) degenerates.
Innervated muscles cannot be stimulated to contract.
Innervated muscle fibres die.
Existing reflexes are weaker or absent.
Muscle tone reduces.
Muscle mass decreased (atrophy) rapidly and severely.
Paresis or plegia.
Neurogenic atrophy (LMN) vs disuse atrophy (ortho dz).
Neurogenic atrophy occurs over days, while disuse atrophy occurs over weeks.
Neurogenic atrophy can be severe and may cause loss of entire muscle mass, while disuse atrophy usually mild-moderate and never causes loss of all muscle mass.
Neurogenic atrophy is localised to the innervated muscles of the affected nerve or nerves (usually focal, but may be generalised w/ generalised nerve disease), while disuse atrophy is not localised to the distribution of a specific nerve.
Why bother w/ neuro exam?
Aim of medicine is to provide prognosis.
Clinical signs of neuro disease can be spectacular, distressing and confusing.
Breaks complex presentations down into manageable steps.
Signs reflect location; not severity.
Location + history give a likely dx and therefore px.
3 basic aims of neuro exam?
Is it neuro? - most important.
If so, where is it? - needs most practice.
What might be causing it? - can be hard to answer.
Cardinal neuro presentations.
Abnormal gait, stumbling, falling.
Abnormalities of the head and face.
Apparent blindness or deafness.
Abnormal bhvr - esp. episodic abnormal bhvr.
Exercise intolerance.
Incontinence.
SHOULD ALL PROMPT A NEURO EXAM
Possible spinal and peripheral localisations.
C1-C5 – UMN signs only.
C6-T2 – UMN signs in HLs
– LMN signs in FLs.
T3-L3.
L4-S2 – LMN both FL and HL.
Generalised neuromuscular.
Single nerve lesion.
First step of the spinal localisation process.
Analyse gait.
- which limbs have a gait disturbance?
- does it look MSK or neuro?
- Painful lameness w/ reduced WB phase and same mistake each time.
- Restrictive lameness w/ altered swing phase and same mistake each time.
- Ataxia is a lack of regulation of limbs in space w/ variable mistake in paw placement each time.
- Plegia is inability to make a movement w/ no visible movement of limbs at an appropriate time.
- Paresis is reduced ability to make a movement w/ under-flexion of limbs, dragging or not moving.
- Weakness is where patient cannot generate enough force in movement and will make appropriate movement if there is no resistance.
Step 2 in spinal localisation process?
Assess proprioceptive responses.
Is each limb normal or not?
RESPONSES INVOLVE THE FOREBRAIN.
Responses involve nerves, brains and spinal cord so act as a screening test; they cannot localise alone!
Hopping test:
- look at foot.
- push body to obscure it.
- foot should come back just into view.
Paw placement test:
- keep body still and stabilise w/ hand under caudal abdomen (pelvic limbs) or under thorax (thoracic limbs).
- turn over paw, trying not to touch pads.
- foot should immediately be replaced.
Step 3 in spinal localisation process.
Assess spinal reflexes, muscle tone, muscle mass.
Normal or abnormal?
Abnormalities due to dysfunction in single or multiple nerves?
Reflex only up to spinal cord and back down.
Reflex testing tests the sensory nerve, the associated segment of brainstem/spinal cord, motor nerve and muscle only.
REFLEXES DO NOT INVOLVE FOREBRAIN!
Reflexes test well-defined sections of the PNS and CNS so are used to pinpoint lesion localisation.
Perineal reflex test:
- tests pupendal nerve and S1-3 spinal cord.
- pinch perineum or tap ischium.
- test L and R.
- interpretation – anus constricts, tail moves ventrally.
- Note: this habituates sometimes so the first reflex is the most reliable.
Pelvic limb withdrawal:
- tests sciatic nerve and L6-S2 spinal cord.
- pinch toe or interdigital web.
- ALL joints flex.
- *hip and stifle flexors have large mass and lots of innervation so are only lost w/ severe LMN disease; focus attention on hock and digits.
Patella reflex:
- tests femoral nerve and L4-L6 spinal cord.
- strike patella tendon.
- stifle extends.
- *can be consciously inhibited in a nervous or tense dog. Always test the dependent limb too.
Cutaneous trunci reflex:
- tests segmental nerve, spinal cord cranial to this up to T1, lateral thoracic nerve.
- pinch skin starting at ilial wing.
- see bilateral contraction of cutaneous trunci muscle.
- *multiple inputs along both sides of spine have only ONCE common output (skin twitch).
Thoracic limb withdrawal:
- sensory = median and ulnar nerves.
- motor = musculocutaneous, median and ulnar nerves.
- pinch toes or interdigital web.
- ALL joints flex.
- *main deficit seen is lifting shoulder and then kicking leg backwards when resistance applied.
Pitfall 1 - thoracic limb withdrawal not that accurate.
Only ~50% accurate to separate cervical spinal cord diseases into C1/5 or C6/T2 lesions:
- not all brachial plexus nerves are tested; a lesion in areas not involving the media, ulnar or musculocutaneous may be missed.
- multiple alternative pathways exist for the reflex arc. A focal , partial lesion may not be severe enough to appreciably reduce the reflex.
- acute C1-C5 lesions almost always temporarily reduce the reflexes.
C1-C5 gait vs C6-T2 gait abnormalities.
C1-C5 = thoracic limbs protracted and extended fully before making contact w/ ground = goose-stepping or floating gait.
C6-T2 = short thoracic limb strides and longer, ataxic strides in pelvic limbs = two-engine gait.
Pitfall 2 - Spinal shock.
Spinal shock = the temporary reduction in spinal reflexes caudal to an acute (severe) spinal cord injury occurring cranial usually to the affected reflex arcs.
Mechanism:
- severe, acute spinal cord injury occurs.
- causes UMN dysfunction (loss or reduction in limb movement).
- loss of UMN facilitation temporarily also reduces LMN function:
– decreased tone.
– decreased reflexes.
– no reduced mass –> only a functional lesion.
Means it can be easy to mistake a focal T3/L3 lesion for a multifocal or diffuse spinal cord disease, which could have a v different px.
Disappointingly confusing!
Dogs w/ little or no pelvic movement movement have some T3-L3 involvement, regardless of pelvic limb reflexes.
T3/L3 and spinal shock will look the same as a dz affecting T3/L3 AND L4/S2.
C1-C5 lesions.
Gait and proprioceptive deficits in all four limbs.
Floating FL gait.
Pelvic limb reflexes intact.
Thoracic limb reflexes may be reduced in acute lesions (spinal shock).
No muscle atrophy.
C6-T2 lesions.
Gait and proprioceptive deficits in all 4 limbs.
2-engine gait.
Pelvic limb reflexes intact.
Thoracic limb reflexes usually reduced.
Muscle atrophy if chronic.
T3-L3 lesions.
Thoracic limbs unaffected.
Gait and proprioceptive deficits in pelvic limbs.
Pelvic limb reflexes usually intact, but may be reduced in spinal shock.
L4-S2 lesions.
Thoracic limbs unaffected.
Gait deficits in pelvic limbs and/or tail.
Loss of one or more pelvic limb reflexes, perineal reflex or anal tone.
Focal atrophy in region of affected nerve.
Generalised NM lesions.
Abnormalities in all 4 limbs.
Short strided gait and exercise intolerance.
Reduced reflexes and/or atrophy in all 4 limbs.
Single nerve lesion.
Focal atrophy and paresis.
Loss of reflex if nerve involved in reflex arc.
