Neurology Part I

What are the components of the forebrain?

The cerebrum and the diencephalon. It lies rostral to the tentorium cerebelli.

What is the cerebrum composed of?

• Cerebral cortex

• White matter

• Basal nuclei

What is the cerebral cortex important for?

• Behaviour

• Vision

• Hearing

• Fine motor activity

• Conscious awareness of touch, pain, temperature and body position

What does the cerebral white matter do?

It conveys ascending and descending sensory and motor activities within and between cerebral hemisphere, as well as to and from the rest of the CNS

What do the basal nuclei do?

They are involved in muscle tone and initiation and control of voluntary motor activity.

Where are the cell bodies of upper motor neurones located?

• In the motor cortex of the pyramidal system

• The diencephalon

• Motor centres of the brainstem (extrapyramidal system)

What does the diencephalon do?

It is involved in autonomic and endocrine functions, sleep and wakefulness, olfactory function, vision and PLR and emotional behavioural patterns via connections with the limbic system.

It also acts as a sensory relay system to the cerebral cortex for the functions of vision, hearing, conscious awareness of pain (nocioception) and body position (proprioception)

Describe the pattern of circling, blindness and loss of postural reactions/proprioception in a forebrain lesion

• Circling TOWARDS lesion

• CONTRALATERAL blindness

• CONTRALATERAL loss of postural reactions & proprioception

What does the brainstem do?

• It contains the regulatory centres for consciousness (ascending reticular activating system), cardiovascular system and breathing (medullary reticular formation)

• Links the cerebral cortex to the spinal cord through ascending and descending motor pathways (known as the long tracts)

• It has 11 pairs of cranial nerves involved in a variety of moto and sensory functions.

What changes to postural reactions are seen in animals with brainstem lesions?

IPSILATERAL loss of postural reaction

What does the cerebellum do?

• It controls the rate, range and force of movements without actually initiating any motor activity.

• It co-ordinates muscle activity and smooths movements once they have been induced by the upper motor neurones

• Maintains posture and regulates muscle tone when the body is at rest or during motion due to its close association with the brainstem vestibular nuclei.

• Has an inhibitory influence on urination

List the four regions of the spinal cord

• Cranial cervical (C1-C5)

• Cervico-thoracic (C6-T2)

• Thoracolumbar (T3-L3)

• Lumbosacral (L4-S3)

What do these spinal segments contain?

The cell bodies of the lower motor neuron.

The segments C6 - T4 and L4 - S3 contain the cell bodies of the LMN which innervate the thoracic and pelvic limbs. Lesions at the level of these intumescences results in what signs in the corresponding limb?

Lower motor neuron signs

The neuromuscular system is composed of motor units that consist of what?

• Neuron cell body

• Axon

• Neuromuscular junction

• Muscle fibres

The lower motor neurone is an efferent neuron connecting the CNS to what?

To a target muscle

What are the locations of a lower motor neuron?

• Ventral horn of the spinal cord grey matter

• Within the cranial nerve nucleus of the brain stem

Describe the connection between a lower motor neuron and a muscle.

The lower motor neuron either lies within the ventral horn of the spinal cord grey matter or within the cranial nerve nucleus of the brainstem.

Its axon leaves the CNS by the ventral roots to join a spinal nerve and a peripheral nerve before it synapses via a cholinergic/nicotinic neuromuscular junction within a muscle

If a single lesion doesn’t explain a lesion localisation, then what else should be considered?

Is this a multifocal lesion or is it diffuse?

What is the difference between a multifocal and a diffuse lesion?

A multifocal lesion affects multiple parts of the nervous system and a diffuse lesion affects globally and symmetrically one or more parts of the nervous system.

What should be assessed during the hands-off examination?

• State of consciousness

• Awareness & behaviour

• Posture & body position at rest

• Gait evaluation

• Identification of abnormal involuntary movements

What should be assessed during the hands on examination?

• Postural reaction testing

• Muscle tone and size

• Spinal reflexes

• Nocioceptive testing

• Cranial nerve evaluation

What does the mneumonic VITAMIN D stand for?

V - vascular

I - inflammatory/infectious

T - traumatic/toxic

A - anomalous

M - metabolic

I - idiopathic

N - neoplastic/nutritional

D - degenerative

Describe the onset and development of a traumatic or vascular spinal event

Sudden onset & non-progressive or regressive

Describe the onset and development of neurological signs relating to metabolic disease

They often wax and wane with time and are bilaterally symmetrical

What are the similarities and differences in onset and progression of neoplastic and inflammatory diseases?

With neoplastic disease, the signs are usually progressive and are often focal, while inflammatory/infectious diseases are progressive but more often multifactorial

See table in notepad for typical changes associated with each pathological process

See table

Give examples of pain spinal conditions

Disk herniation

Discospondylitis

Fracture/luxation

Extramedullar tumour

Inflammatory eg myelitis

Give examples of non-painful spinal conditions

Ischaemic myelopathy

Degenerative myelopathy

Vertebral malformation

Intra-medullary tumour

What do the functional segments of the spinal cord contain?

The cell bodies of the lower motor neuron

Lesions at the level of C6-T2 and L4-S3 result in what signs to the corresponding limb?

LMN signs

What does a normal gait require intact function of?

• Cerebellum

• Brain stem

• Spinal cord

• Sensory & motor nerves

• Neuromuscular junction

• Muscles

Define ataxia

An unco-ordinated gait that can arise from a peripheral nerve or spinal cord lesion (general proprioceptive ataxia), a vestibular lesion (vestibular ataxia) or a cerebellar lesion (cerebellar ataxia)

List the possible neurolocalisation for proprioceptive ataxia

This is the general proprioceptive pathway and includes:

• Peripheral nerve

• Dorsal root

• Spinal cord

• Brainstem

• Cerebral cortex

What are the clinical signs of proprioceptive ataxia?

Abnormal postural reactions with limb paresis

List the neurolocalisations for vestibular ataxia

Within the vestibular apparatus

• Vestibular nuclei (central)

• Vestibular portion of CN VIII

• Peripheral vestibular receptors

What are the clinical signs of vestibular ataxia?

• Head tilt, leaning, falling or rolling to one side

• Abnormal nystagmus, strabismus

• Normal (peripheral) or abnormal (central) postural reactions in case of unilateral dysfunction

• Crouched posture, reluctance to move and wide head excursion in case of bilateral dysfunction

What are the clinical signs of cerebellar ataxia?

• Broad based stance, swaying of the trunk

• Intention tremours of the head

• Loss of balance on both sides as well as backwards and forwards

• Dysmetric gait

• Pendular nystagmus

• Delayed then exaggerated response to postural reaction testing

• Ipsilateral menace deficit with normal vision

• Absence of limb paresis and normal mentation

What is the upper motor neurone system responsible for?

• Initiation and maintenance of normal movements

• Maintenance of tone in the extensor muscles to support the body against gravity

Where can the cell body of an upper motor neurone system be located?

• Cerebral cortex

• Basal nuclei

• Brainstem

• Spinal cord

The upper motor neuron system travels through the brain and/or spinal cord white matter and synapses indirectly via an interneuron with a LMN to do what?

Modulate its activity (essentially inhibitory). The UMN pathways are responsible for stimulating the appropriate LMN that induce the postural and protraction phases of locomotion.

Define paresis

Paresis is a loss of ability to support weight (LMN) or inability to generate a gait (UMN). It implies that some voluntary movement is still present.

Describe UMN paresis

UMN paresis causes a delay in the onset of protraction, which is the swing phase of the gait

Why do most cases of UMN paresis also cause some degree of general, proprioceptive ataxia?

Due to the close anatomical relationship within the caudal brainstem and the spinal cord.

Lesions affecting the forebrain cause contralateral or ipsilateral paresis?

Contralateral. It is usually so mild that it is not usually apparent in the gait.

LMN paresis affects the gait with lesions in what locations?

• Peripheral nerves

• Neuromuscular junction

• Muscle

Motor deficits observed are ipsilateal to the lesion

Describe LMN paresis

LMN paresis reflects degrees of difficulty in supporting weight and varies from a short stride to complete inability to support weight, causing collapse of the limb whenever weight is placed on it.

Lower motor neuron disorders do not cause ataxia, but only paresis. True or false?

True

Brainstem injury is unlikely to cause paralysis or paresis without what additional signs?

• Altered state of consciousness

• Vestibular ataxia

• Cerebellar ataxia

• Cranial nerve signs

Describe the differences in gait with an animal with lower motor neuron disease vs upper motor neuron disease

LMN: Short-strided gait and decreased ability to support weight

UMN: Long-strided, reaching and stiff gait

Animals with a caudal cervical lesion are often described as having a two-engine gait, with a short & choppy gait in the thoracic limbs and a long-strided, floating gait in the pelvic lumbs

What tests are preferred over proprioceptive placing in the cat, when testing postural reactions?

• Hopping response

• Wheelbarrowing

• Tactile placing

Increased resistance when assessing muscle tone by flexing and extending the limb and joints is indicative of UMN signs but can also be seen in what situations?

• Fractious, excitable or painful animals

• In association with LMN paresis affecting the flexor system

What change to tone is a hallmark of LMN signs?

Diminished tone

The withdrawal reflex in the thoracic or pelvic limbs does not depend on the animal’s conscious perception of noxious stimuli. What is it instead?

A segmental spinal cord reflex that depends on the function of the local spinal cord segments

The patellar reflex is elicited by hitting the patellar ligament and observing what?

A reflex contraction of the quadriceps muscle and extension of the stifle joint.

The patellar reflex evaluates the integrity of what spinal cord segments?

L4-L6 and the femoral nerve.

What is the extensor reflex?

This is a test of the extensor system and involves lifting the contralateral leg and assessing if the animal can keep all the joints extended and can stay upright

How can you explain (in terms or neurolocalisation) normal spinal reflexes in the forelimbs and hindlimbs?

This is a neuromuscular disorder

What results in an UMN bladder?

• Lesion cranial to the S1 segment

Describe a UMN bladder

• Conscious voiding attempts usually absent

• Bladder catheterisation difficult

• Large bladder

• May get overflow incontinence when the bladder becomes over distended

Are the perineal tone and reflex present with an UMN bladder?

Yes

What results in a LMN bladder?

A lesion caudal to the S1 segment

Describe a LMN bladder

• Conscious voiding attempts absent

• Bladder easily emptied

• Half-full to large flaccid bladder

• Perineal tone and reflex reduced to absent

• Frequent urine dribbling

Describe the grading system in sensory testing

Grade 1: Pain only, no neuro signs

Grade 2: Paraparesis

Grade 3: Paraplegia with intact bladder function

Grade 4: Paraplegia with loss of bladder function

Grade 5: Paraplegia with loss of bladder function and no nociception

The cutaneous trunci reflex enables accurate localisation within what UMN spinal cord segments?

T3 to L3 UMN spinal cord segments

What else does the cutaneous trunci reflex assess?

The C8-T1 region of the brachial plexus

Describe how to perform the cutaneous trunci reflex

Stimulate the skin with a pinprick or by pinching with a pair of haemostats, starting at the iliac crest, approx 1 inch lateral to the midline.

This should result in bilateral contraction of the CT muscles

In the absence of such muscle contraction, the point of skin stimulation should be moved cranially until a normal reflex is observed

Stimulation more than two vertebral segments caudal to the lesion will not elicit a reflex

Intervertebral disk disease can occur in area of the spinal cord caudal to where?

C1-C2

Why is there a low incidence of intervertebral disk extrusions in the thoracic spine between T2 and T11?

Due to the presence of the intercapital ligament

What age of dog is most commonly affected by IVDD?

Middle aged

Describe the difference between Hansen type I and Hansen type II intervertebral disk abnormality

Type 1: Usually seen on chondrodystrophic breeds which have chondroid metaplasia. These risks usually extrude rather than protrude

Type 2: Most commonly seen in older, larger, non-chondrodystrophoid dogs with fibroid metaplasia of the disk. These disks usually protrude rather than extrude.

What are the clinical signs of IVDD?

• Spinal pain

• Varying degrees of limb dysfunction

• Root signature > affected limb may be held flexed off the ground

What abnormalities can be seen in a dog with IVDD on x-rays?

• Collapse of IVD space

• Deformities of the intervertebral foramina

• Radio-opaque material in or around the spinal cord

• Decrease in the size of the dorsal articular joint space

Mildly affected animals (with pain alone or mild paresis) with IVDD may be managed with cage confinement for at least how long?

2 weeks

With IVDD, how long should you consider cage confinement for?

Up to 1-2 weeks after the animal is clinically normal

Animals that retain nociception have a what percentage chance of being able to walk at some time after surgery for IVDD?

90% chance

When nociception is absent with IVDD, what is the percentage chance that the animal will be able to walk at some time after surgery? How about if nociception is absent for >48h

50%; 5%

What is a fibrocartilaginous embolism?

A syndrome of acute spinal cord infarction caused by embolisation of fibrocartilage material

Why is histopathological evaluation necessary to establish a definitive diagnosis of FCE?

Because other conditions can cause spinal cord infarction, such as neoplastic emboli, parasitic embolism assoc with microfilariasis, septic emboli associatd with bacterial endocarditis or other infection, hyperlipidaemia, possible microinfarction or hyperviscosity.

In what clinical situation should you suspect a FCE?

• Acute, paroxysmal then non-progressive signs of a focal myelopathy

What breeds are predisposed to FCE?

Giant breeds, esp Great Dates but can occur in small breeds too, most commonly Min Schnauzer and Sheltie. Tends not to occur in chonondrodystrophoid dogs.

What is the mean age of animals affected by FCE?

3-7 years

Describe the onset and progression of an FCE

Peracute and non-progressive

More than ½ of cases with FCE are following what?

Exercise or trauma (not necessarily severe) as they may be factors in increasing pressure within the intervertebral disc.

Why can clinical signs occasionally get worse over the first 24h with an FCE?

Due to the development of spinal cord injury. After this, FCE is usually non-progressive unless ascending and descending myelomalacia develops.

Is an FCE a compressive or non-compressive spinal cord disease?

Non-progressive

Are patients with FCE classically painful or non painful on manipulation or palpation of the spine?

Non-painful, though a very small percentage of dogs may initially show mild spinal hyperaesthesia associated with the actual extrusion of fibrocartilaginous material and stimulation of nociceptive receptors in the bone, periosteum, ligaments and meninges.

Describe the neurolocalisation of an FCE

Usually focal or multifocal and can be either symmetrical or asymmetrical (due to the asymmetric branching of the intrinsic spinal cord vasculature. Emboli can occur anywhere in the spinal cord so LMN or UMN signs can be observed. However, a large proportion of FCE localise to the cervico-thoracic or lumbo-sacral intumescence.

Histopathological evaulation is necessary to establish a definitive diagnosis of FCE. Its antemortem diagnosis is essentially a rule out one, based on what clinical history and results of neurological examination?

Peracute to acute onset of non-progressive spinal cord dysfunction in a non-chondrodystrophoid breed with focal or multifocal symmetrical or asymmetrical non-painful spinal cord neurolocalisation

List the differentials for acute spinal cord dysfunction

• FCE

• Acute disk herniation

• Spinal fracture or lucation

• Inflammatory CNS diseases

CSF analysis can be normal in the case of an FCE, but what changes can be seen?

• Xanthochromia

• Elevated TP

• Pleocytosis with majority of non-degenerate polymorphonuclear cells in the acute phase

How do you treat a FCE?

Medically with supportive care and physiotherapy

• Free radical scavengers are recommended in the acute phase to limit secondary ischaemic complications. Methylprednisolone sodium succinate 30mg/kg iv (Only in first 8 hours). Past this therapeutic window, c’steroid treatment is not indicated and could potentially be harmful

Recovery from FCE is determined by what?

The degree of spinal cord damage. The prognosis for functional recovery is usually good with some animals keeping residual deficits, especially in cases of intumescence involvement and LMN signs.

Failure to make any improvement after 2 weeks. is usually suggestive of a poor prognosis.

Animals with absent nociception have a guarded to poor outcome.

Degenerative myelopathy is a degenerative disease of the spinal cord commonly recognised in dogs. What breed of dog is most commonly affected?

GSD

Can degenerative myelopathy occur in the cat?

Yes

What parts of the nerve are affected by CDRM?

• The axon

• The myelin sheath in the spinal cord

• Nerve roots

What age of animal are most commonly affected by CDRM?

5-11 years

What are the clinical signs of CDRM?

Non painful, slowly progressive thoracolumbar meylopathy causing an UMN bilateral paraparesis.

Some dogs may also show a loss of the patellar reflex due to the involvement of the dorsal root of the femoral nerve

CDRM is often insidious and mistaken for what conditions?

OA

HD

What is the course of the disease of CDRM?

5 months —> 2 years