Neurological Examination - Dog & Cat

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Introduction

The neurological examination is one of the most important and cost-effective tools in clinical neurology.

The two aims of a neurological examination are:

To determine if the nervous system is affected in a disease process
To establish an accurate anatomical diagnosis, to localise the lesion

It is important to localise the lesion before considering differential diagnoses, as it is the location of the disease within the nervous system (not the disease) that determines the clinical signs.

There are essentially 8 regions that the lesion can be assigned to:

Forebrain
Brainstem
Cerebellum
C1 - C5 spinal cord
C6 - T2 spinal cord
T3 - L3 spinal cord
T4 - cauda equina
Neuromuscular

Tools useful for the neurological examination include: quiet room, chair, yoga mat, reflex hammer, haemostats, Q-tips, cotton balls, penlight, lens.

A full physical examination including an orthopaedic and musculoskeletal examination should be performed prior to a neurological examination. Any noxious tests such as a rectal exam should be delayed until afterwards.

There are 8 parts of the neurological examination are as follows:

Mentation

The animal's level of consciousness can be assessed: it may be alert, obtunded, stuporous, semicomatose, comatose.

The animal's quality of consciousness may be appropriate or inappropriate, showing compulsion or dementia.

The most common site for a lesion to cause progressive obtundation is the brainstem, due to the presence of the reticular activating system at this level.

Posture

The head:

a tilt suggests vestibular disease
a turn suggests a forebrain disease

The limbs:

wide-based stance suggests proprioceptive loss
narrow-based stance suggests weakness
decreased weight-bearing may be an evidence of pain

The body:

decerebrate posture: neck and limbs extended, no mentation
decerebellate posture: neck and forelimbs extended, hindlimbs flexed, mentation ok
Schiff-Scherrington posture: forelimbs rigid, hindlimbs flexed, mentation ok, due to a spinal lesion at T3-L3
Neck ventroflexion: neuromuscular weakness

Gait

The animal should be walked or observed to walk on a non-slippery surface. A normal gait requires the integration of proprioceptive and motor systems. Therefore the gait exam is assessing for both paresis and ataxia.

Paresis

There may be a failure to generate the gait or to support the weight of the animal.

Lower motor neuron paresis: the walk is short-strided, there is a tendency for collapse, bunny hopping and neck flexion.

Upper motor neuron paresis: the stride is spastic and there is stiffness. There are usually proprioceptive deficits as well, which present as knuckling and a swaying gait.

Ataxia

Ataxia refers to incoordination, and comes in three qualities:

Sensory ataxia: which accompanies UMN paresis and refers to a swaying gait and knuckling.
Vestibular ataxia: loss of balance shown as a head tilt, a tendency to fall or roll to one side, abnormal nystagmus
Cerebellar ataxia: uncontrolled limb movements, abnormal rate and range of movements shown as hypermetria, intention and postural tremors.

Postural reactions

Postural reactions require the integration of proprioceptive and motor systems. Useful reactions to test include: paw positioning, hopping, wheelbarrowing, hemiwalking, tactile or visual place and the extensor postural thrust.

A deficit in these reactions may show a deficit in conscious proprioception, but a failure to return the paw to a normal position may also be caused by a LMN denervation of the digit extensors or a UMN paresis.

Spinal reflexes

Ideally these spinal reflexes will be diminished to absent in LMN disorders and increased in UMN disease.

It is important to evaluate the tone and spinal reflexes together with the gait abnormality. Dogs can exhibit profound neuromuscular paresis with myasthenia gravis and still have normal tone and reflexes. Similarly some dogs with T3 - L3 lesions often have normal muscle tone and reflexes.

The animal should be placed in lateral recumbency and be as relaxed as possible.

Tests include: the patellar reflex, the biceps reflex and the triceps reflex.

The withdrawal reflex is done by squeezing a digit to cause withdrawal of the limb.

The perineal reflex tests the pudendal nerve.

The cutaneous trunci reflex involves pinching the skin on either side of the trunk and assessing contraction of the cutaneous trunci muscle.

A decreased or absent reflex may show: a lesion within the reflex arc, physical limitation of movement due to joint fibrosis or muscle contracture, excitement and fear.

An exaggerated reflex may indicate a lesion to UMN pathways cranial to the spinal cord segments tested, or may simply be due to excitement and fear.

Cranial Nerves

The cranial nerve exam should be done when the patient is the most relaxed. It can be done "by the numbers" or by region. Either part or all of cranial nerves II through to VIII are evaluated in the region of the eyes.

Vision can be evaluated by assessing response to dropping cotton wool in front of the animal or watching it follow something in the distance. It assesses cranial nerve II and the forebrain. Occasionally it is necessary to set up a maze of objects in the animal’s environment to see if they can avoid the objects when walking around them.

The menace response is a learned response and may not occur until 10 to 12 weeks in puppies and kittens. This also assesses cranial nerve II, but also the forebrain, cerebellum, brainstem and cranial nerve VII.

The pupillary light response assesses cranial nerve II, the brainstem and cranial nerve III.

A fundic exam at this point may also be helpful.

Strabismus or abnormal nystagmus may signify lesions in the nerve which are motor to extraocular muscles, such as cranial nerve III, IV and VI.

Facial sensation and integrity of cranial nerve V is assessed with the palpebral reflex and the corneal reflex, which also involve cranial nerve VII and VI respectively.

Cranial nerve V is also motor to the muscles of mastication and there may be atrophy of these muscles, or an inability to close the jaw.

Cranial nerve VII dysfunction may appear as facial paresis or asymmetry. The palpebral reflex and the menace response will be absent.

CN VIII dysfunction can lead to deafness, or vestibular signs such as a head tilt or abnormal nystagmus.

Cranial nerves IX and X can be assessed by testing the gag reflex.

Hypoglossal nerve (XII) dysfunction will be seen as tongue dysfunction, either paresis, atrophy or deviation.

Palpation

This should first be light and assess any swelling or atrophy of muscles.

Deep palpation may reveal pain in an area.

This should be a systematic exam, and contralateral limbs can be used to compare size and shape.

Nociception

Superficial pain involves perception of cutaneous pain.

Deep pain involves testing periosteal nociception, by applying increased pressure on a digit with haemostats for example.

The presence or absence of nociception is important for prognosis, and loss of deep pain perception signifies a poor prognosis as it is the last function to be lost.

Further investigation

The neurological examination should enable an anatomical diagnosis to be established. It may be important to consider if one lesion can explain all deficits, or if the disease is more diffuse or multifocal.

The next step is to investigate the area involved, common tests and diagnostic include:

Clinical pathology: haematology, biochemistry, serology, microbiology, CSF analysis
Diagnostic imaging: radiography, ultrasound, CT, MRI
Electrophysiology: nerve conduction studies, brainstem auditory evoked potentials, electro-encephalography
Tissue biopsy: nerve, muscle, brain


Neurological Examination - Dog & Cat Learning Resources
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Feline Medicine Q&A 14
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Sample Book Chapters
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Neurological examination and lesion localisation
Small Animal Neurological Emergencies
Simon Platt, Laurent Garosi
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References

Kenny, P. (2009) Neurological examination RVC neurology student notes

DeLahunta, A. (2001) Braund's Clinical Neurology in Small animals: Localization, diagnosis and treatment IVIS




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