Contributors: Rodney Bagley, Kyle Braund, Simon Platt
Species: Canine | Classification: Miscellaneous
- Clinical evaluation of animals suspected of having nervous system disease requires a fundamental knowledge of neuroanatomy and neurophysiology.
- More important is an understanding of how discrete elements within the nervous system are integrated, interrelate and interact for the animal to perform various normal functions.
- Examination should be undertaken in a systematic manner so that no part of the examination is omitted.
Functional Components of the Nervous System
- The major components of the nervous system include:
- The brain.
- Nerves arising from the brain (cranial nerves).
- The spinal cord.
- The peripheral nerves.
- These components are connected to, and interact with, each other in order to control most bodily functions.
- The brain is housed within the skull and is important for controlling:
- Consciousness (mental status, awareness).
- Voluntary and reflex movements of the head, body and limbs.
- Vital functions such as sleeping, eating, drinking and breathing.
- Conscious recognition of senses (seeing, hearing, taste, touch, and pain).
- Using the level of the tentorium cerebelli as a dividing point, the brain can be separated into the structures rostral to the tentorium cerebelli, ie the supratentorial structures, also called the forebrain and structures caudal to the tentorium, ie the infratentorial structures.
- The supratentorial structures include:
- The cerebral hemispheres.
- Basal nuclei.
- Supratentorial structures provide for many conscious functions such as vision and voluntary movement.
- Portions of the cerebral hemispheres, eg the parietal cortex, sense where the limbs and head are in space.
- Recognition of the orientation of where the body is with relation to gravity is referred to as proprioception.
- The diencephalon (hypothalamus and thalamus) controls many autonomic and basic life-support functions, eg eating, drinking, body temperature regulation.
- Infratentorial structures include:
- Mid brain.
- Medulla oblongata (portions of the brain stem).
- The brain stem contains the groups of neurons (nuclei) which make up many of the cranial nerves (III-XII), as well as the reticular activating system (which via the cerebral cortex keeps the body in an alert and awake state).
- Recognition of the need for, and the drive to maintain, breathing is controlled by areas within the caudal brain stem.
- Many ascending and descending neural pathways important for movement also course through, or originate within, the brain stem.
- The cerebellum, which is immediately dorsal to the pons and medulla oblongata, smoothes and co-ordinates movements and is important for unconscious control of proprioceptive functions.
- The spinal cord houses pathways that connect the brain to the peripheral nerves. It contains variable numbers, depending upon the species, of spinal cord segments.
- These segments are anatomically divided into the following regions:
- Cervical (C) (8 segments).
- Thoracic (T) (13-18 segments).
- Lumbar (L) (5 - 7 segments).
- Sacral (S) (3-6 segments).
- Caudal (Ca) (5+ segments).
- Clinical signs of spinal cord dysfunction often manifest as abnormalities of limb strength and movement.
- The peripheral nerves arise from within the spinal cord (motor nerves) or nerve root ganglia (sensory nerves) and bring information from (sensory) or carry information to (motor) parts of the body such as the muscles of the limbs.
- Motor nerves provide information to the muscle through a special connection known as the neuromuscular junction.
- The motor component of these nerves form the final pathway wherein information from the brain is conveyed to the body in order to perform a function such as muscle movement.
- Components of the clinical neurological examination are used to test the complex normal interactions of these structures to determine if the nervous system is working properly.
Goals of the Neurological Examination
- The goals of the neurological examination are to establish that the disease involves the nervous system and to determine the location of the lesion(s) within the nervous system.
- Often diseases affect discrete portions of the nervous system and clinical signs reflect this focal abnormality.
- Some diseases however, affect multiple areas of the nervous system. Clinical signs will usually reflect the diffuse nature of such lesions.
- After localization of the problem, and consideration of the signalment and historical disease course, a realistic differential diagnosis list can be formulated.
- Diagnostic tests are next chosen to ascertain the ultimate diagnosis.
- An accurate diagnosis provides information important for formulation of a treatment plan and realistic prognosis for the owner.
The Neurological Examination
- The signalment is important as many diseases are breed, age or sex-associated.
- Breed-associated diseases of dogs and cats have been previously summarized (see references).
- In addition to a general history, questions should address the clinical problem (the chief complaint), the duration and clinical course (progressive, unchanged, or improving; persistent or episodic).
- Specific questions such as exposure to toxic substances and the possibility of similar disease in related or in-contact animals are asked depending upon the presenting complaint.
- Important historical aspects to clarify include:
- Travel, eg exposure to endemic infectious agents.
- Vaccinations, eg for canine distemper, rabies.
- Recent drug therapies, eg metronidazole toxicity to the vestibular system.
- Any previous systemic illness.
- With episodic clinical signs, the relationship of these signs to eating, eg signs after eating more often seen with hepatic encephalopathy Hepatic encephalopathy , whereas signs seen long after eating may be associated with hypoglycemia Hypoglycemia.
- A subjective observation and evaluation by viewing the animal from a distance can be made as the history is obtained.
- It is best to allow the animal to move freely, unless unduly aggressive or likely to escape, while watching for its response to the environment.
- Lead or direct animal towards objects which it must avoid.
- An exception to this approach would be where a vertebral injury is suspected. In this situation, the animal is restrained and immobilized as soon as possible. The neurological examination will need to be adapted to accommodate for such restraint.
- Abnormal posturing and movement are usually observed at this stage.
- Animals may wander, head press or become somnolent.
- Animals with severe brain stem, spinal cord, or peripheral nerve disease, will often not be able to stand and walk.
Level of consciousness (mental status) and behavior
- The cerebral cortex is the ultimate source of awareness.
- The ascending reticular activating system (ARAS) within the brain stem receives input from the environment via all parts of the body and sends stimuli to the cerebral cortex to maintain a wakeful state.
- Consciousness is interpreted as normal when certain stimuli evoke a similar response in the animal being examined as is expected in normal animals.
- The most severe state of impaired consciousness is coma Small animal coma score. In this situation, animals are recumbent and have no response to any external stimuli, including stimuli that are painful.
- Animals with stupor or semi-coma are similarly not responsive to external stimuli. However, their responsiveness to painful stimuli remains although reactions observed may not clearly be directed toward the stimuli.
- Depression, delirium and dementiaare terms taken from human medicine to describe abnormal demeanors associated with psychological abnormalities. They suggest a state of altered consciousness or personality change that is not as severe as stupor and coma and are used figuratively, rather than literally, when describing animal activity. Since it is impossible to determine what an animal is thinking, these terms may be inappropriate for use in veterinary medicine.
- Narcolepsy Narcolepsy refers to excessive daytime sleepiness that is usually episodic and results in abnormal consciousness.
- Breeds predisposed to narcolepsy include Doberman Pinscher Dobermann , Labrador Retriever Retriever: Labrador , Miniature Poodle Poodle: miniature , Dachshund Dachshund , Beagle Beagle , and Saint Bernard St Bernard.
- Cataplexy is periodic muscular hypotonia.
Posture and body position at rest
Abnormal posture of the head
- Examine for normal head position.
- With a head tilt, the median plane of the head is rotated from its normal perpendicular relationship with the dorsal plane.
- When severe, the head tilt may be associated with rolling or falling toward the side of the tilt.
- A head tilt is most often associated with disease of the vestibular system.
The tilt is usually directed towards the side of the lesion.
- Occasionally, with central lesions involving the caudal cerebellar peduncle or flocculonodular lobe, the head tilt is directed away from the side of the lesion; the so-called paradoxical vestibular syndrome.
- The adversive syndrome consists of a head turn and circling.
- This occurs most often with supratentorial lesions.
- The head turn and circling are usually directed toward the side of a unilateral supratentorial lesion.
- A similar abnormality, termed hemi-inattention or hemi-neglect may be seen when an animal will only eat from one side of the food container.
Abnormal posture of the limbs
- Standing with the limbs placed more lateral than usual is a wide-based stance and may be associated with a variety of lesions within the nervous system, especially those involving the vestibular system, cerebellum, and spinal cord.
- Spasticity is increased extensor tone of muscles, most often seen in the limbs.
- Spasticity can be seen at rest or while moving and is usually associated with disease of central nervous system motor pathways.
- Decerebrate rigidity is characterized by opisthotonus (extreme dorsal extension of the head and neck towards the back) and extension of all limbs.
- Usually the animal is stuporous or comatose.
- This is due to loss of descending input from supratentorial structures to the medullary centers normally responsible for flexion of the limbs.
- This posture is seen with severe brain stem lesions.
- Decerebellate rigidity is characterized by opisthotonus with thoracic limb extension and flexion of the pelvic limbs up under the body due to contraction of the sublumbar muscles.
- Mental status is normal.
- This posture is associated with cerebellar disease.
- If the lesion involves the ventral aspects of the cerebellum, extensor rigidity of all limbs is seen.
- This posture can occur episodically where it may be referred to as "cerebellar seizures".
- Schiff-Sherrington posture (phenomenon) is characterized by thoracic limb extension with normal tone and reflexes in the pelvic limbs.
- This results from a severe third thoracic (T3) to third lumbar (L3) spinal cord segment lesion that interrupts the ascending inhibitory impulses to the extensor muscles of the thoracic limbs.
- Except for extension, the thoracic limbs are neurologically normal.
- This feature, along with results of the pelvic limb examination, should help differentiate this posture from extensor rigidity occurring as a result of an abnormality of the central pathways cranial to the sixth cervical (C6) spinal cord segment.
- Severe extensor rigidity of the limbs, neck, trunk, and tail is characteristic of tetanus .
- Classically, a "saw-horse" stance is seen.
- Facial muscle contraction may result in a "tense" facial expression termed risus sardonicus.
Nerve root signature
- A persistent or episodic non-weightbearing lameness, presumably the result of nerve irritation and pain, is termed nerve root signature.
Abnormal posture of the trunk
- Scoliosis, an abnormal lateral deviation of the vertebral column, often occurs secondary to intramedullary spinal cord lesions such as syringo- or hydromyelia.
- Kyphosis, an abnormal flexion primarily of the thoracolumbar spine, results in a "hunched-back" appearance.
- Lordosis is abnormal extension of the vertebral column particularly in the thoracolumbar region.
- This results in a concave appearance of the vertebral column when the animal is viewed from the side.
- Tremor is an involuntary, rhythmic, oscillatory movement of all or part of the body.
- It results from the alternate or synchronous contraction of reciprocally innervated, antagonistic muscles.
- Tremor can be localized to one body area or be generalized to involve the whole body.
- Localized tremor usually involves the head or pelvic limbs.
- A tremor that is more obvious when an animal tries to perform a task, eg such as eating, is referred to as intention tremor and is most commonly associated with cerebellar dysfunction.
- Myoclonus is a shock-like contraction of one muscle or a group of muscles.
- Clinically, it is seen as explosive movement of part of the body, particularly limb flexion.
- Myoclonus in dogs usually is a sequele to distemper infection Canine distemper disease which establishes a pacemaker-like depolarization of local motoneurons.
- Reflex myoclonus is characterized by episodic, stimulation-evoked extensor rigidity of the body and is most commonly seen in Labrador Retrievers Retriever: Labrador and Dalmatian Dalmatian dogs.
- Seizures Seizures are an important and common sign of intracranial neurological disease.
Abnormalities of gait
- Induce animal to walk, run and, if possible, ascend and descend steps.
- Gait refers to the method of moving the limbs and body in order to get from one place to another and is commonly defined as a regularly repeating series of limb movements during walking or running Gait analysis.
- Ataxia is a lack of co-ordination Ataxia.
- Dysmetria indicates improper measurement of range and force in muscular act.
- Dysmetria can include both characteristics of hypometria and hypermetria.
- Spasticity is a state of increased muscle tone and commonly occurs with lesions of the white matter tracts of the brain stem and spinal cord.
- This is observed in the gait as stiffness or floating (failure to adequately flex the limbs during gait).
- Stiffness associated with decreased stride length is commonly seen with diseases of the peripheral neuromuscular apparatus (motor neurone cell body, nerve roots, peripheral nerve, neuromuscular junction and muscle).
- A similar appearance may occur in animals with limb pain, primarily as a consequence of orthopedic disease such as polyarthritis Arthritis: polyarthritis - Greyhound.
- Animals with neuromuscular disease may also have a stiff, stilted, choppy gait due primarily to muscle weakness.
- Myotonia refers to persistent muscle contraction following voluntarily or external initiation.
- Animals with myotonia often have a stiff gait.
- Muscles of the body may dimple when percussed (struck with a reflex hammer).
- Myotonia occurs as a congenital problem in various breeds of dogs such as the Chow-Chow Chow Chow.
- Paresis or neurologic weakness indicates decreased motor effort without complete paralysis.
- Lameness is an abnormal gait wherein there is reduced ability or desire to bear weight on a limb due to pain or a mechanical restriction of normal joint movement.
- It is usually associated with pain of the limb from musculoskeletal disease. However, it may result from nerve root disease (see nerve root signature).
Conscious proprioception testing
- Conscious proprioception testing is used to determine if the animal is conscious of where a limb is placed .
- This is evaluated by placing the paw in an abnormal position, ie turning the paw over on the dorsum, and determining how quickly the animal corrects the paw position.
- A normal animal corrects the abnormal paw position, ie moves it back to a normal position, immediately (less than 1 sec); a delay or failure to do so strongly suggests nervous system disease.
- Hopping tests proprioception, strength, and voluntary movement.
- To perform hopping, the animal's weight is placed exclusively on one limb and the animal's body is forced in one direction.
- When the animal's center of gravity, ie the shoulder area in the thoracic limb, moves laterally to the foot, the limb should quickly be moved laterally to accommodate the new body position.
- A delay in this movement is abnormal.
- Animals with neuromuscular weakness such as myasthenia gravis Myasthenia gravis will not be able to hop normally when most of their weight is placed on one limb but will hop normally when the examiner supports the majority of the animal's weight.
Wheelbarrowing, hemiwalking, extensor postural thrust
- For wheelbarrowing, the front or rear of the animal is raised so that the animal's weight is placed on either both pelvic or both thoracic limbs.
- The animal is then forced by the examiner to move the body forward (when testing the thoracic limbs) and backward (when testing the pelvic limbs).
- During hemiwalking, a thoracic and pelvic limb on one side are held up by the examiner and the animal is forced laterally in the opposite direction.
- When the animal is moved laterally, the limbs contacting the ground move laterally to accommodate this new body position.
- To perform the extensor postural thrust test, the animal is suspended in the air by picking it up under the thoracic limbs and then lowering it toward the ground.
- As the animal is lowered, prior to touching the ground, the pelvic limbs will extend.
- As the animal actually touches the ground, it will begin to walk backwards.
- Testing of placing reactions is most practical for small animals that can easily be held off of the ground.
- Non-visual, tactile placing reactions are assessed first.
- The animal is held in the examiners arms suspended off the ground with its eyes covered.
- When the animal is moved by the examiner toward the edge of a table or other edged surface and the dorsal aspect of the animal's paw touches the table, the animal should bring the limb forward to rest on the table-top.
- Such non-visual placing yields information similar to hopping and conscious proprioception tests concerning the integrity of the nervous system.
- Visual placing (performed similarly, although without the eyes covered) may help in defining a visual deficit.
- Normal tactile placing with a deficit in visual placing indicates a lesion in the visual pathways.
Abnormal postural reactions
- If postural reaction testing reveals abnormalities of limb function , these abnormalities are described as follows:
- Paraparesis - abnormal postural reactions in the pelvic limbs bilaterally.
- Monoparesis - abnormal postural reactions in only one limb.
- Tetraparesis - abnormal postural reactions of all four limbs.
- Hemiparesis - abnormal postural reactions of a thoracic and pelvic limb on the same side.
- There is currently no descriptive term for bilateral postural reaction abnormalities of the thoracic limbs only.
Cranial nerve examination
- The cranial nerves are evaluated systematically, some being assessed individually and some assessed in functional groups.
Olfactory-Cranial Nerve (CN) I - smell
- Smell can be assessed by placing a substance that is aromatic, eg baby food, but non-irritating around the nasal opening so the vapors can be exposed to the nasal mucosa.
- This should evoke a behavioral response (turning away, contraction of the facial muscles, sniffing) that indicates the animal recognizes the substance.
- Irritating substances will excite sensory (free nerve) endings of the trigeminal nerve (CN V).
Optic - CN II - vision
- Cranial nerve II function can be assessed in many ways, the simplest being evaluation of the menace response.
- This test is performed by making a menacing gesture (moving the hand quickly toward the eye) and assessing for the normal blinking response (closure of the palpebral fissure).
- Also obstacle test and visual placing responses.
- Assessment of the pupils:
- When stimulated, CN III constricts the pupil and the sympathetic system dilates the pupil.
- Initially the pupils are assessed for size and symmetry.
- A resting inequality in pupil size is termed anisocoria
- Pupils may be smaller than normal and sluggish to respond to light due to iridic vascular congestion and deemed to be associated with anterior uveitis Uveitis.
- Painful conditions of the cornea may cause miosis.
- An abnormality of sympathetic innervation to an eye can result in a miotic pupil alone or in signs of complete sympathetic denervation of the orbit (Horner's Syndrome Horner's syndrome ).
- Clinical signs of sympathetic denervation of the eye include miotic pupil, prolapsed third eyelid Nictitans gland: prolapse , ptosis Proptosis / prolapse orbit / globe , enophthalmos, and peripheral vasodilation.
- A dilated, poorly or non-responsive pupil is indicative of parasympathetic denervation or loss of muscle tone of the iris.
- Parasympatholytic drugs such as atropine instilled in the eye will dilate the pupil.
- Primary disease of the iris such as iris atrophy is common in older animals especially dogs.
- A dyscoric pupil and an irregular pupillary margin may be clues of underlying iris disease.
Oculomotor - CN III - eye movement; pupillary constrictiction
- If the motor function of CN III is abnormal, the eye may be deviated from a normal position. This is termed strabismus.
- Lesions of this portion of CN III produce a lateral and ventral strabismus and also ptosis due to paralysis of the levator palpebrae muscle.
- In some instances, dysfunction of the oculomotor nerve will not result in a strabismus, but the eye will be unable to move medially.
Trochlear - CN IV - ocular movement
- Lesions of the trochlear nerve or nucleus cause a contralateral dorsomedial strabismus.
- In species with a round pupil, no strabismus is seen.
- Fundic examination of the retina with a direct ophthalmoscope however, reveals the superior retinal vessels to be deviated laterally.
Abducent - CN VI - ocular movement
- Disease of CN VI results in a ventromedial strabismus.
Clinical abnormalities CN III, IV and VI combined
- Paralysis of all muscles responsible for eye movement is termed complete ophthalmoplegia.
- Cranial nerves III, IV, VI, the sympathetic innervation and CN V (ophthalmic branch) lie ventral in the skull within the cavernous venous sinus which encircles the pituitary fossa.
- Strabismus seen only when the head is forced into an abnormal orientation is termed positional strabismus.
- This clinical abnormality is almost always associated with an ipsilateral central or peripheral vestibular lesion.
Trigeminal - CN V - facial sensation, motor to muscles of mastication
- The trigeminal nerve supplies sensory innervation to the head and motor innervation to the muscles of mastication.
- There are three major branches of this nerve:
- The ophthalmic branch of CN V is sensory to the eye and surrounding skin.
- It can be tested by assessing for a palpebral reflex (afferent - CN V; efferent CN VII).
- The maxillary branch supplies sensory innervation to the maxillary area.
- This function is assessed by touching the external nasal mucosa, preferably with the animal's eyes covered.
- The mandibular branch of CN V is assessed by stimulation of the skin overlying the mandiblar area and also by assessing for muscle tone, function, and atrophy of the temporal and masseter muscles.
- An animal with bilateral mandibular nerve disease will have a dropped jaw and be unable to close its mouth.
Facial - CN VII - motor to muscles of facial expression, taste, salivation and skin sensation inside of ear
- The facial nerve has branches coursing to:
- The lacrimal gland (major petrosal nerve).
- The salivary glands and tongue (chorda tympani branch).
- Muscles of facial expression (buccal and auriculopalpebral branches).
- Clinical signs of a lesion of the facial nerve usually include paresis or paralysis of facial muscles resulting in facial asymmetry.
- Keratoconjunctivitis sicca (KCS) Keratoconjunctivitis sicca or dry eye may be seen with involvement of these nerves.
Vestibulocochlear - CN VIII - equilibrium, balance and hearing
- Clinical signs of vestibular disease include ataxia, head tilt, nystagmus and positional strabismus.
- The vestibular system can be abnormal due to disease of CN VIII (peripheral) or its nuclear regions (central).
- Every attempt should be made to initially determine whether the vestibular abnormality is due to a central or peripheral lesion.
- Clinical assessment of hearing: hearing can subjectively be evaluated by creating a loud noise in the environment (without creating other vibration currents) and assessing for ear (Pryer's reflex), eye and other body movements suggesting that the animal has heard.
Glossopharyngeal - CN IX - pharyngeal sensation and movement (with CN X), salivation, taste
- Lesions of CN IX cause difficulty in swallowing and pharyngeal muscle abnormalities.
- This function is evaluated by stimulating a gag or swallow reflex, most easily elicited by the examiner placing a finger or hand in the caudal aspect of the animal's throat.
Vagus - CN X - laryngeal sensation, laryngeal movement, salivation and other autonomic functions, taste
- Lesions of this portion of CN X, along with the accessory branch of CN XI, the recurrent laryngeal or caudal laryngeal nerve, result in paralysis of the laryngeal muscles.
Spinal accessory - CN XI - motor innervation to trapezius muscle
- Lesions in this nerve result in atrophy of the trapezius muscle.
- Decreased resistance to lateral passive movement of the head and neck contralateral to the side of the lesion may be noted.
Hypoglossal - CN XII - motor to the tongue
- Test for tongue motility.
- Clinical signs of disease of CN XII include problems with deglutition, prehension, mastication and vocalisation.
- The tongue will be weak or paralyzed.
- Reflex functions are involuntary activities that do not require conscious thought.
Thoracic limb reflexes
- Spinal reflexes of the thoracic limb include the extensor carpi radialis, the biceps, the triceps and withdrawal or flexion reflexes.
- The extensor carpi radialis and the triceps reflexes assess the radial nerve with cell bodies in the spinal cord segments C7-T1.
- The biceps reflex assesses the musculocutaneous nerve (spinal cord segments C6-C8).
- These reflexes are elicited by percussing the muscle belly or tendon of insertion of the individual muscles and observing for the appropriate muscular response:
- When the extensor carpi radialis is percussed, the carpus should extend slightly due to contraction of this muscle.
- When the triceps is percussed, slight elbow extension is observed.
- When the biceps muscle is stimulated, slight elbow flexion may be seen.
- With the latter reflex, movement may be slight and not visualized.
- The examiner, however, may feel the muscle contract by placing a finger over the muscle during percussion.
- The withdrawal reflex is elicited by pinching the skin of the foot or pastern region with a hemostat and looking for flexion of the carpal and elbow joints in order to move the paw away from this stimulus:
- This reflex assesses all major nerves of the thoracic limb including the radial, ulnar, median, musculocutaneous and axillary nerves.
- A decreased or poor response is seen when the animal cannot adequately flex the limb away form the stimulus.
Pelvic limb reflexes
- Reflexes assessed in the pelvic limb include the patellar, cranial tibial, gastrocnemius and flexion or withdrawal reflexes.
- The patellar reflex:
- Assesses the femoral nerve which arises from the L4-L6 spinal cord segments.
- Is performed by lightly tapping the straight patella ligament overlying the stifle joint and looking for a quick extension of the stifle.
- The cranial tibial and gastrocnemius reflexes:
- Assess the sciatic nerve (spinal segments L6-S1) specifically the peroneal and tibial branches, respectively.
- When the cranial tibial muscle is percussed, slight hock flexion is seen.
- Percussion of the gastrocnemius muscle results in hock extension.
- The withdrawal reflex of the pelvic limb:
- Assesses integrity of the sciatic nerve (spinal segments L6-S1).
- As in the thoracic limb, the reflex is elicited by pinching the skin of the foot and looking for flexion of the hock and stifle joints to move the foot away from the stimulus.
- Decreased ability to flex the hock is usually the most notable abnormality when sciatic disease is present.
- Sometimes with sciatic disease, the patellar reflex may concurrently appear hyper-reflexic.
- This is not due to an additional UMN lesion, but results from the loss of sciatic nerve innervation to the antagonistic muscles of this reflex (pseudohyper-reflexia).
- Reflex function of the anal sphincter is assessed by stimulating the peri-anal area and seeing the anus contract (anal reflex).
- With anal stimulation, the tail will often be flexed concurrently although a light stimulus can result in reflex tail elevation (tail reflex).
- Bowel - may be fecal incontinency with lesion L4-S3.
- This reflex is mediated through the pudendal nerve to the anal sphincter.
- The pudendal nerve arises from the S1-3 spinal cord segments.
- Anal contraction can also be elicited by squeezing the penis of a male dog or the clitoris of a bitch.
- In some instances, rectal examination or palpation to assess the tone of the anal sphincter may be useful.
Other reflex functions
The cutaneous trunci reflex
- Tests superficial pain receptors, the spinal cord and the lateral thoracic nerves.
- This reflex is elicited by pinching or pricking the skin over the dorsal thoracolumbar trunk.
- The efferent response is contraction of the cutaneous trunci muscles bilaterally.
- Skeletal muscles are evaluated for atrophy by visual inspection and palpation.
- The muscles are compared for size, consistency and tone on both sides simultaneously.
- This is most easily accomplished in the standing animal.
- Disuse atrophy may occur with UMN lesions and is generally slow in progression and less severe than LMN atrophy.
Neurogenic abnormalities of urination
- With ascending sensory pathway involvement, the bladder may not be recognized as full.
- With descending UMN motor pathway involvement, bladder emptying is interrupted.
- This will result in a large bladder.
- Because the local peripheral nerves (S1-S3 spinal cord segments) to the bladder are not impaired, the bladder has good tone, ie it feels turgid, and because of hyper-reflexia of the bladder outflow region, the UMN bladder is difficult to express.
- This is the same concept as hyper-reflexia of the patellar reflex seen with UMN lesions.
- After a period of time (usually around 2 weeks) reflex bladder expression may begin to occur.
- With LMN lesions affecting the sacral spinal segments or associated peripheral nerves, the bladder is again large because the ascending and descending information cannot project through the damaged peripheral nerves.
- Bladder tone is decreased, and the bladder feels flaccid ("jelly-like").
- Additionally, the bladder is easily expressed because the local tonic reflex to maintain tone in the bladder outflow tract is not present.
Evaluation of pain and sensation
- Sensory neuropathies include:
- Propioceptice deficits.
- Hyporeflexia/areflexia without muscle atrophy.
- Self mutilation.
- Hyperesthesia is defined as increased sensitivity to stimulation.
- Deep pain is assessed by placing increasing pressure with a hemostat or similar instrument on the toe or pastern region of the affected foot and looking for either vocalizing, attempts to bite the examiner, or immediate orientation of the body towards the area of stimulation.
- If one of these does not occur, deep pain is absent.
- If an animal only withdraws its limb from such a stimulus, it must not be concluded that deep pain perception is present.
- Such withdrawal function is purely reflex activity and will be present even in an animal that has its spinal cord transected cranial to the level being tested.
Ancillary diagnostic aids
- After lesion located, determine nature of disease process by consideration of breed, age, history.
Few absolute rules apply to occurrence of neurological disorders.
- Confirm by use of ancillary diagnostic aids.
- To evaluate general health of individual.
- To identify/rule out metabolic disorders affecting nervous system.
- To (rarely) provide definitive diagnostic information, eg hepatic insufficiency.
- Cerebrospinal fluid (CSF) analysis Cerebrospinal fluid: culture and sensitivity.
- Test for CSF pressure, physical appearance, cellularity and protein content.
- Collect from cisternal magna or lumbar subarachnoid space (less satisfactory).
- Structural CNS lesion (brain/spinal cord).
- Spinal cord diseases where diagnosis not apparent by other means, eg radiology.
Collect CSF before contrast media injected.
- Multifocal neurological disease.
- Peripheral polyneuropathies (may be due to nerve root disease).